This Document Contains Chapters 10 to 12 CHAPTER 10: HOW CELLS DIVIDE WHERE DOES IT ALL FIT IN? Chapter 10 begins a new conceptual theme by addressing the cell cycle and replication. It provides students the principles of asexual reproduction in prokaryotes and eukaryotes. It is important to briefly review the basic cell structure information in Chapter 4 before proceeding with Chapter 10. The information in Chapter 10 is crucial for students to understand the principles of sexual reproduction and embryology covered later in the book. SYNOPSIS Cellular division in bacteria is simple since the genome is one double-stranded circle of DNA attached to the interior of the cell at a single point. Duplication is an enzyme mediated process that begins at that point and continues around the circle resulting in two side-by-side DNA circles. Physical division occurs when the cell attains a certain size. New membrane materials are laid down between the points of attachment of the DNA circles and pinch inward, binary fission. Eukaryotic cell division is more complicated because the eukaryotic genome is larger and more complex. Eukaryotic chromosomes are linear structures composed of chromatin, mostly DNA and protein with a small amount of RNA. Eukaryotic DNA is a long double-stranded fiber. Every 200 nucleotides it coils around a core of eight histone polypeptides forming a nucleosome. The string of nucleosomes is further wrapped into supercoils. Heterochromatin is highly condensed chromatin while euchromatin is relatively uncondensed. Some portions of the DNA are permanently heterochromatic to prevent DNA expression; the remainder is uncondensed at the proper time to facilitate transcription. The number of chromosomes in eukaryotic organisms varies widely from species to species. Human cells possess a diploid complement of 23 homologous pairs of chromosomes each with a characteristic appearance. Prior to cell division each homologue replicates producing two identical sister chromatids joined by a common centromere. The process of growth and division in a typical eukaryotic cell is called the cell cycle and is composed of five phases. The G1 phase is the cell’s primary growth phase while the genome is replicated during the S phase. During the G2 phase, various organelles are replicated, the chromosomes start to condense, and microtubules are synthesized. All of these are preparatory for mitosis or M phase. Actual cell division occurs in the final C phase, cytokinesis. Mitosis is a continuous process that is divided into four stages for ease of examination: prophase, metaphase, anaphase, and telophase. Much of the preparation for mitosis occurs during interphase, a collective stage that includes G1, S, and G2. Preparations include chromosome replication, centriole replication (in animals only), and tubulin synthesis. Chromatin condensation begins near the end of interphase and continues through prophase when individual chromosomes become visible. At the same time, the nuclear envelope breaks down and the centrioles of animal cells move apart. One set of microtubules assembles between the nucleolar organizing regions while another set grows outward from each centromere toward the poles. Metaphase begins when the pairs of sister chromatids align across the center of the cell at the metaphase plate. The end of this phase is signalled by the division of the centromeres. During anaphase, each chromatid moves toward the pole to which it is attached. Separation occurs when the central spindle fibers slide past one another, moving the poles farther apart. The chromatids also move toward the poles as the microtubules to which they are attached shorten. The nucleus begins to reform around the uncoiling chromosomes during telophase. The spindle apparatus breaks down and the nucleolus reappears as rRNA genes are again expressed. There are significant differences in cytokinesis in animals and plants. Animal cells are pinched in two by a belt of constricting microfilaments at the cleavage furrow. Rigid plant cells are not easily deformed and divide from the inside outward. This expanding partition is called the cell plate. The final addition of cellulose to either side of the membrane results in two separate cells. Cell cycle control is based on a check-point feedback system. When certain conditions at a checkpoint are met, the cell proceeds to the next stage of activity or division. Cyclin-dependent kinases (Cdk’s) and cyclins are intimately associated with these control processes. Unicellular organisms make independent decisions on whether or not to divide. Multicellular organisms must limit independent cell proliferation to maintain the integrity of the whole. Eukaryotes utilize various growth factors to do this. Disruption of these control mechanisms is characteristic of cancer. LEARNING OUTCOMES 10.1 Bacterial Cell Division is Clonal 1. Diagram the bacterial cell cycle. 2. Describe the events of DNA partitioning and cell fission. 10.2 Eukaryotes Have Large Linear Chromosomes 1. Differentiate between haploid and diploid numbers of chromosomes in a species. 2. Describe the structure of a eukaryotic chromosome. 10.3 The Eukaryotic Cell Cycle Is Complex and Highly Organized 1. Describe the events of the five stages of the eukaryotic cell cycle. 10.4 During Interphase, Cells Grow and Prepare for Mitosis 1. Describe the events that take place during interphase, and how they affect the structure of the centromere after S phase. 10.5 In Mitosis, Chromosome Segregate 1. Describe how the mitotic apparatus forms during prophase. 2. Describe how chromosomes attach to the spindle during prometaphase. 3. Describe how the chromatids align at the cell equator in metaphase. 4. Describe how, when the chromatids separate during anaphase, chromatid cohesion prevents premature separation. 5. Describe how the nucleus re-forms during telophase. 6. Compare cytokinesis in plant and animal cells. 10.6 Events of the Cell Cycle Are Carefully Regulated 1. Contrast the effects of cyclins and cyclin-dependent kinases on cell division. 2. Distinguish the roles of the three key checkpoints in the eukaryotic cell cycle. 3. Explain the role of cyclin-dependent kinases in mitosis. CONCEPT MAP Concept mapping is a structured graphical presentation of the concepts covered in a particular topic. The following concept map represents the links between the information covered in this chapter. It is important to tell students to develop their own concept maps after covering the particular information covered in class. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 10 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that binary fission is the same as mitosis • Students do not distinguish between the cell cycle and mitosis • Students believe asexual reproduction is restricted to microorganisms only. • Students conceptualize all DNA as being X-shaped • Students do not distinguish between the terms chromatin and chromosomes • Students believe that spindles work like rubber bands during replication • Students are not aware that endosymbionts are attached to spindles • Students are not fully aware that mitochondria and chloroplasts self-replicate • Students believe that asexual reproduction always produces identical offspring cells • Students believe asexual reproduction results in weakness and sexual reproduction always produces stronger individuals • Students think haploid cells have half the traits needed to make an organism • Students have the idea that cancer is merely a condition of uncontrolled cell division • Students believe that all tumors are cancerous INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE It is more efficient to move by packing your belongings in boxes and bags than to move each item individually. Similarly, condensing the chromatin into discrete chromosomes makes it easier to separate them during mitosis. Remember the order of mitotic stages via PMAT (or IPMAT if interphase is included). Any student named Matthew deserves apologies on this mnemonic! Stress that the purpose of mitosis is to produce many identical copies of a cell. Most students merely memorize when the nucleolus disappears and reappears. If they associate its presence with its function synthesizing rRNA, it is obvious when the transient organelle will be present and when it will be absent. Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 10. Application • Have students explain how drugs that alter cytoskeleton function would affect mitosis in animal cells. • Have student explain why food poisoning is likely to occur if foods such as meats are sitting at room temperature for 30 to 60 minutes. • Ask students why bacterial infections spread more quickly on the skin than yeast infections. Analysis • Ask students to explain what would happen to offspring cells if the centromeres did not separate easily during anaphase. • Ask students to explain why diabetes, a condition in which glucose is not taken up readily by cells, slows down mitosis. • Have students explain how amino acid deficiencies can affect the progression of the G1 phase of the cell cycle. Synthesis • Ask students to think about the properties of a drug that would selectively harm cancer cells without causing death or injury to normal body cells undergoing cell division. • Have students develop a rationale for the use of a chemical that causes telomeres, the tips of chromosomes, to shorten rapidly during mitosis. • Ask students come up with a strategy that would inhibit binary fission without affecting the mitosis of microorganisms. Evaluation • Ask students to evaluate the effectiveness of an anticancer drug that inhibits the formation and growth of blood vessels. • Ask students to support or debate the claim that nicotine, which affects cytoskeleton function, reduces the body’s ability to repair damaged body parts. • Have the evaluate why using stem cell treatments that replace dead cells are more likely an effective treatment for repairing brain damage than for treating wounds to the skin. VISUAL RESOURCES 1. Bring in a ball of yarn to simulate DNA as chromosomes and some unraveled yarn to represent DNA in chromatin form. Question the likelihood of knitting a scarf with the yarn in a ball. This is like trying to transcribe DNA as chromosomes. Also question the ease of separating two bunches of identically colored yarn when unraveled as compared to the same yarn when rolled into two separate balls. 2. In a small classroom, use clay or plastic foam and colored straws to represent chromosomes. In a large classroom with an overhead projector, cut rod-shaped chromosomes out of colored acetate. Make a second set to show chromatid replication during the S phase and hold the two chromatids together with overlapped post-it-note centromere circles. Cut similar-shaped, but different-colored chromosomes to show homologues. 3. Use colored beads and two sets of spaghetti to simulate chromosomes and spindle microtubules in a cell bounded by yarn. The pieces of spaghetti anchored at the poles push the yarn boundary apart as they slide past one another. Shorten the spaghetti attached to each chromosome to move the chromosomes to the poles. (One might want to use string instead of spaghetti, but the latter is more accurate. 4. The DNA content of bacteria can be illustrated using an audiocassette. The cassette represents a single bacterium. Pulling out all of the tape (without tearing it away from the cassette) represents the amount of uncoiled DNA in a single bacterium. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Name That Phase Introduction Laboratory sessions on animal and plant cell mitosis are often confusing adventures for students. In addition, it is difficult for instructors to troubleshoot every student’s microscope issues in large laboratory section. This demonstration assists students with recognizing the stages of mitosis before a laboratory session. It can also be used as a quick review strategy for tests the ask students to recognize or describe the stages of mitosis. Materials • Computer with internet access • Downloaded PDF images found at the Jdenuno website: http://www.jdenuno.com/PDFfiles/Mitosis.pdf#search=%22mitosis%20images%22 • LCD projector • Laser pointer Procedure and Inquiry 1. Show the low power image of the onion root tip slide. Ask students to name the structure and tell if the tissues making up the structure are growing or mature. Have them explain their answers. 2. Then show the close-ups of the dividing cells and use the laser pointer to select various cells at different stages of mitosis. 3. Ask the students to identify the stages and explain what features of the cells gave them a clue to their answers. 4. Show the low power image of the whitefish blastula slide. Ask students to name the structure and tell if the tissues making up the structure are growing or mature. Have them explain their answers. 5. Then show the close-ups of the dividing cells and use the laser pointer to select various cells at different stages of mitosis. 6. Ask the students to identify the stages and explain what features of the cells gave them a clue to their answers. B. Modeling Cell Division Introduction This fun activity asks students to be model of cell division using various craft and hobby materials. It reinforces retention of the cell features and cell events involved in binary fission and mitosis. Materials • Small paper plates • Scissors • Assorted dried noodles & spaghetti • Assorted color pipe cleaners • Glue • Colored markers or crayons • Cellophane tape • Wrapping twine • Assorted buttons Procedure & Inquiry 1. Have students break up into teams of two. 2. Assign them to a particular stage of mitosis or cell cycle 3. Tell them they must make a accurate model of the that stage of binary fission, mitosis or cell cycle 4. Have the students show the model to the class and explain each feature including the justification for using a particular craft or hobby material to represent a cell structure. LABORATORY IDEAS Influencing Mitosis: Onion Roots as a Model Have students perform a simple long-term experiment using onion root tip growth as a model for investigating factors that affect mitosis. a. Tell the class that they will be using onion root elongation as a model for investigating factors that affect mitosis. b. They will be growing onions on shallow bowls containing water. c. Let students know that they can grow the onions under different environmental conditions or add various chemicals to the water. d. Provide students with the following materials: a. Fresh onion with intact roots b. One shallow bowl for onion c. Soap water d. Toothpicks e. Small metric rulers f. Access to microscopes g. Access to microscope slides and cover slips h. Access to methylene blue i. Access to water supply j. Access to incubators k. Access to refrigerator l. Chemicals for testing affects on mitosis i. Nicotine solution (cigarettes soaked in a 100 ml per cigarette solution of 50% V/V alcohol water solution ii. Broadleaf weed killer iii. Grass weed killer iv. Caffeine – dark coffee or caffeine tablets dissolved in a 100 ml per cigarette solution of 50% V/V alcohol water solution v. Plant fertilizer solution vi. Other chemicals can be selected at the discretion of the instructor or student e. Tell the students to carry out the following procedure. a. Ask the students to use the soap water to gently rinse any growth inhibitors off of the base of the onion and the roots. b. Have the students use the toothpicks and bowls to make a set up in which the onions are suspended over the water. The bottom of the onion must be preserved. c. Ask the students to design an experiment in which they use mitosis of onion root tips cells as a indicator of chemicals that inhibit mitosis. d. Let this experiment run until the roots of a control onion have grown at least 5 cm. e. Ask the students to explain their results after the period of time it takes the roots grow 5 cm. f. Have students explain the mechanism by which the growing conditions or chemicals specially affect mitosis in the root tip. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. Students who have successfully mastered the content of Chapter 10 can apply their knowledge for service learning activities in the following ways: 1. Have students do a presentation about the biology of cancer to scout groups or elementary school students. 2. Have students design and prepare an electronic presentation of cell division for school teachers. 3. Have students tutor middle school or high school biology students studying cell replication. 4. Have students work with a cancer awareness organization at a health fair. ETYMOLOGY OF KEY TERMS acro- beginning; end; tip (from the Greek akro- topmost; extreme) allo- divergence; difference from; other (from the Greek allos- other) ana- up; back (from the Greek an- up) bi- two (from the Latin bi- two) centri- center (from the Greek kentron- center) chrom- color (from the Greek chroma- color) cyto- of, or relating to, the cell (from the Greek kytos- cell) di- two; twice (from the Greek di- two) eu- good; well; true (from the Greek eu- well) haploid one set of chromosomes (from the Greek haploeides- single) hetero- different (from the Greek heteros- the other of two) homologous to say the same (from the Greek hom- same and legein- to say) karyo nucleus of a cell (from the Greek karyon- nut or kernel) -kinesis movement (from the Greek kinein- to move) Kinetochore specialized point of attachment for fibers (from the Greek kinein- to move and choros- place) meta- change; transformation; following something in a series (from the Greek meta- change) mito- thread (from the Greek mitos- a thread) mono- one; single; alone (from the Greek monos- alone) nucleus kernel (from the Latin nux- nut) poly- many (from the Greek polys- many) pro- before; for; in front of (from the Greek and Latin pro- for or before) some body (from the Greek soma- body) sub under; beneath; below (from the Latin sub- below) tel- end (from the Greek telos- ultimate end) tetra- four (from the Greek tettares- four) tri- three (from the Greek tri- three) zygote diploid cell created by fertilization (from the Greek zygotes- yoked) CHAPTER 11: SEXUAL REPRODUCTION AND MEIOSIS WHERE DOES IT ALL FIT IN? Chapter 11 continues the coverage of cell reproduction covered in Chapter 10 by applying the concepts to sexual reproduction. Students are likely to confuse the events and details of mitosis and meiosis. It is important to reinforce to students the differences and similarities of asexual and sexual cellular division. Students should also be told upfront the goals and outcomes of meiosis before proceeding with detailed coverage of Chapter 11. Chapter 10 should be regularly referenced to help reinforce the principles of Chapter 12. SYNOPSIS Meiosis and syngamy constitute a cycle of sexual reproduction. Fertilization would double the chromosome number of each subsequent generation except that the gametes possess only a haploid complement of DNA. Thus the resultant zygote inherits genetic material from both its father and its mother, in the case of humans, twenty-three chromosomes from each. Sexual reproduction produces offspring that are genetically different from either parent while asexual reproduction produces progeny that are genetically identical to the parent cell. The specific events of sexual reproduction varies from kingdom to kingdom. For example, in most unicellular eukaryotes, the individual cells function directly as gametes. In plants, specific haploid cells are produced by meiosis, these cells then divide by mitosis to form a multicellular haploid phase which further produces eggs and/or sperm. In animals special gamete-producing cells differentiate from the other somatic cells early on in development. Only these cells are able to undergo meiosis to create haploid eggs or sperm. Gamete-producing cells differentiate from somatic cells early in development. While they themselves are diploid, their products are haploid as a result of meiosis. Although meiosis and mitosis share many features, including microtubule formation, meiosis is unique for three reasons: synapsis, homologous recombination, and reduction division. During synapsis homologous chromosomes physically pair along their length. In homologous recombination genetic exchange, called crossing over, occurs between the homologues. Reduction division is the two separate rounds of nuclear division that occur in the remainder of the process. In the first division, homologous chromosomes pair, exchange material, and separate. No genetic replication occurs before the second division when the non-identical sister chromatids separate into individual gametes. Each division is composed of prophase, metaphase, anaphase, and telophase, additionally labeled I or II. Some of the most important events of meiosis occur during prophase I. The ends of the sister chromatids attach to specific sites on the nuclear envelope. The attachment sites for the two homologues are near one another ensuring that each chromosome associates closely with its homologue. Each gene corresponds with its partner forming the synaptonemal complex. Certain genes are exchanged between homologues, an event called crossing over. The homologues are released from the membrane but remain tightly connected to one another. The homologues line up along the central plate of the cell during metaphase I. Only one face of each centromere is accessible to microtubule attachment, thus each homologue attaches to only one polar spindle fiber. The microtubules shorten at anaphase I and pull the homologues apart to opposite ends of the cell. Each pole ends up with a complete set of haploid chromosomes. Telophase I finishes division I, cytokinesis may or may not occur. Meiosis II is essentially a mitotic process. During metaphase II, the still connected sister chromatids line up along their new metaphase plate with spindle fibers from each pole attached to each centromere. During anaphase II, the centromeres split and the sister chromatids are drawn to opposite poles. The result is four cells containing a haploid complement of genetic material. Sexual reproduction is advantageous to species that benefit from genetic variability. However, since evolution occurs because of changes in an individual’s DNA, crossing over and chromosome segregation is likely to result in progeny that are less well-adapted than their parents. On the other hand, asexual reproduction ensures the production of progeny as fit as the parent since they are identical to the parent. Remember the adage, “if it’s not broken, don’t fix it.” There are several hypotheses regarding the evolution of sexual reproduction. One is associated with repairing double-stranded DNA breaks induced by radiation or chemicals. The contagion hypothesis suggests that sex arose from infection by mobile genetic elements. The Red Queen hypothesis theorizes that sex is needed to store certain recessive alleles in case they are needed in the future. Along similar lines, eukaryotic cells build up large numbers of harmful mutations. Sex, as explained by Miller’s rachet hypothesis, may simply be a way to reduce these mutations. The “whole truth” is likely a combination of these factors. Regardless of how and why, the great diversity of vertebrates and higher plants and their ability to adapt to the highly varied habitats is indeed a result of their sexual reproduction. LEARNING OUTCOMES 11.1 Sexual Reproduction Requires Meiosis 1. Compare the number of chromosomes in gametes and zygotes. 2. Differentiate between life cycles based on timing of meiosis and fertilization. 11.2 Meiosis Features Two Divisions with One Round of DNA Replication 1. Describe the process of homologous pairing. 11.3 The Process of Meiosis Involves Intimate Interactions Between Homologues 1. Describe the consequences of how homologous chromosomes pair in prophase I. 2. Explain the importance of monopolar attachment of homologoue pairs at metaphase I. 3. Compare the loss of cohesion between sister chromatids at the centromere and on the arms of anaphase I. 4. Identify the key event that occurs during telophase I. 5. Describe the events of meiosis II. 11.4 Meiosis Has Four Distinct Features 1. Discuss the molecular mechanisms responsible for the four distinct features of meiosis. 2. Describe the differences in chromatid cohesions in meiosis and mitosis. 3. Explain the importance of the suppression of replication between meiotic divisions. 11.5 Genetic Variation Is the Evolutionary Consequence of Sex 1. Explain the ways in which meiosis increases genetic variability, and why this is important. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 11 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that sexual reproduction is merely for increasing populations • Students have trouble with the concept of somatic cells and germ cells • Students do not distinguish between the function of somatic and sex cells • Students commonly confuse the terms mitosis and meiosis • Students believe chromatin and chromosomes are identical in nature • Students believe the DNA is doubled only in mitosis and not in meiosis • Students believe that meiosis has an interphase II • Students are not able to accurately calculate chromosome number differences between meiosis I and meiosis II • Students are confused by the terms “N” and “2N” • Students are confused when homologous chromosome separation occurs • Students are confused when chromatin separation occurs in meiosis • Students cannot contrast between the terms fertilized egg and zygote • Students believe that only germ cells carry X and Y chromosomes • Students believe that only animals, and not plants carry out meiosis • Students believe that only higher plants carry out sexual reproduction INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE Meiosis is like roommates splitting up and dividing their belongings. The division is more equitable if the towels are piled together and then divided up, the silverware piled together and divided and so forth, than if things are arbitrarily thrown into one pile or another as they are found. The first method ensures a more even distribution of items and is analogous to homologue pairing. Differentiating between mitosis and meiosis is like distinguishing between the production of cars and trucks. Each uses the same machinery, but produces an entirely different product. The evolution of reproduction adds a second step ahead of the first, like the evolution of PS II/PS I photosynthesis. The second division of meiosis is equivalent to the single division of mitosis, chromatids separate from one another. It is slightly different from mitosis in that the sister chromatids are not identical. The first division of meiosis is a new event. The homologues pair, form synaptonemal complexes, and then move to the metaphase plate. Stress the importance of crossing over and the random assortment of homologues as they relate to producing genetic variation. Meiosis results in (1) genetic variation and (2) the reduction of the genetic complement in preparation for syngamy. It is part of the sexual reproductive process. A thorough understanding of meiosis is necessary to grasp what occurs in Mendelian genetics. It is amazing that Mendel was able to formulate his ideas without knowledge of either mitosis or meiosis. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 11. Application • Have students describe the “day in a life of DNA” during a meiosis event. • Have students explain which stage would be best to study chromosome number and identity during meiosis. • Ask students a major reason why children some children look more like one parent why others appear to have a mixture of both parents. Analysis • Ask students to compare and contrast mitosis with meiosis II. • Ask students explain meiosis in an organism with a 4N complement of DNA. • Ask students explain why crops that have a 3N chromosome complement do not produce viable seeds and pollen. Synthesis • Ask students predict the effects on reproduction if germ cells underwent meiosis I without being following by meiosis II. • Have students explain why offspring produced by two organisms with two different chromosome amounts would have trouble producing germ cells. • Asks students determine the probable use of a chemical that inhibits the S phase of interphase during meiosis. Evaluation • Ask students to benefits an athlete may derive by resting and eating performance athletic event. • Ask students explain the benefits of citrus plants that contain zygotes and parthenogenetic offspring in the same seed. • Have students evaluate the possible effects on humans of a pollutant the increases the probability of chiasma formation. VISUAL RESOURCES Faculty can utilize similar visuals as in mitosis, but with a distinction between homologues and a resulting halving of the genetic complement. Construct a model of the chiasmata as indicated in the text using two strands of thick yarn representing the chromosomes and a ring representing the chiasmata. IN-CLASS CONCEPTUAL DEMONSTRATIONS A. “DNA in Motion” Introduction Role playing is a fun activity to do with students as a means of reinforcing the fate of DNA during meiosis. This activity helps student’s visualize the events of meiosis. It particularly focuses on the segregation and separation of DNA in the different phases of gamete formation. Materials • 8 Student volunteers • 4 XL white T-shirts with “maternal” written large on front and back in black ink. ○ One shirt should also have Chromosome 1 written on the front and back ○ One shirt should also have Chromosome 2 written on the front and back • 4 XL white T-shirts with “paternal” written large on front and back in black ink. ○ One shirt should also have Chromosome 1 written on the front and back ○ One shirt should also have Chromosome 2 written on the front and back • 4 sheets 8 ½“ by 11” pink paper • 4 sheets 8 ½“ by 11” blue paper • 8’ x 8’ section of floor marked with chalk or tape Procedure & Inquiry 1. Introduce the topic of meiosis and discuss the fate of the DNA. 2. Call 8 students to the front of the room and instruct them to wear the T-shirts. 3. Hand the “maternal” students 8 ½“ by 11” pink paper. 4. Hand the “paternal” students 8 ½“ by 11” blue paper. 5. Have one full set of “maternal” and one “paternal” students stand in the 8’ x 8’ section of floor. There should be one “maternal chromosome 1”, one “maternal chromosome 2”, one “paternal chromosome 1”, and one “paternal chromosome 2” in the square. 6. Explain to the class that the students represent maternal and paternal chromatin in a diploid cell. 7. Ask the class to explain the genetic makeup of the cell. 8. Then represent the end of interphase by inviting another full set into the box. Have the students hold hands with their twin chromosome. There should be four chromosomes - two chromosome 1 and two chromosome 2. 9. Ask the class to explain what happened to the genetic makeup of the cell. 10. Have the students line up by homologous chromosomes pairs to represent the beginning of meiosis I. 11. The closer homologues should be asked to swap paper sheet representing crossing over. 12. Ask the class to explain what happened to the genetic makeup of each chromosome. 13. Then represent the end of meiosis I by asking the homologues to separate by moving to opposite ends of the box. 14. Ask the class to explain what happened to the genetic makeup of offspring cells. 15. Follow this up by asking the paired chromatids to split by moving away to the front and back sections of their side of the box explaining that gametes were formed. 16. Ask the class to explain what happened to the genetic makeup of final offspring cells. B. “Attack of the Giant Chromosomes” Introduction This role playing is a fun activity that asks students to develop a play that represents the difference between mitosis and meiosis. It particularly focuses on the separation of DNA in mitosis and meiosis. Materials • 8 Student volunteers • 8 large swimming “pool noodles” ○ Four noodles of one color ○ Four noodles of another color • Paper diagram comparing mitosis and meiosis • Projected image of diagram comparing mitosis and meiosis • Sheets of paper to write a script Procedure & Inquiry 1. Review the basic outcomes of mitosis and meiosis. 2. Call 8 students to the front of the room and instruct them to use the diagram and the noodles to come with a demonstration that shows the difference between mitosis and meiosis. 3. They should be given 5 minutes to plan a “play” for the rest of the class. The play should visually demonstrate the differences in DNA distribution during mitosis and meiosis. 4. Have the students present the play to the class. 5. Ask the class to critique the series of events and provide comments about accuracy of the “play”. 6. The class can redirect the play to demonstrate the concepts more accurately if necessary LABORATORY IDEAS Have students use microscope slides of fungal spores to see the outcomes of crossing over. a. Tell the class that they will be investigating the effects of crossing over on the properties of fungal spores. Explain that these spores are produced by meiosis. b. Provide students with the following materials a. Microscope b. Crossing over in Sordaria whole mount microscope slide c. Sheet of paper to calculate rate of crossing over. c. Ask students to observe the slide and identify the spores d. Tell them to count the number of spores in each chain of spores (should be eight) e. Have them recognize the different color spores (darker or purple, and lighter or tan) f. Ask the students to notice and record any patterns of color distribution on each chain of spores. g. Ask the students to count and record the total number of darker or non-crossing over spores per specimen on the slide. h. Ask the students to count and record the total number of lighter or crossing over spores per specimen on the slide. i. Then ask the class to calculate the percent of spores that exhibit crossing over. j. Have the students place each group of student’s data on the board to calculate the percentage overall for the class. k. Students can be asked to perform a Chi Square test to see if the crossing over rate for their specimen was statistically the same as the class average. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students design high quality laminated meiosis and sexual reproduction flash cards for use in the college library or high school study centers. 2. Have students design an educational PowerPoint presentation about meiosis for middle school teachers. 3. Have students tutor middle school or high school biology students studying meiosis and sexual reproduction. 4. Have students judge science fair projects related to cell division. ETYMOLOGY OF KEY TERMS acro- beginning; end; tip (from the Greek akro- topmost; extreme) allo- divergence; difference from; other (from the Greek allos- other) ana- up; back (from the Greek an- up) bi- two (from the Latin bi- two) centri- center (from the Greek kentron- center) chrom- color (from the Greek chroma- color) cyto- of, or relating to, the cell (from the Greek kytos- cell) di- two; twice (from the Greek di- two) eu- good; well; true (from the Greek eu- well) haploid one set of chromosomes (from the Greek haploeides- single) hetero- different (from the Greek heteros- the other of two) homologous to say the same (from the Greek hom- same and legein- to say) karyo nucleus of a cell (from the Greek karyon- nut or kernel) -kinesis movement (from the Greek kinein- to move) kinetochore specialized point of attachment for fibers (from the Greek kinein- to move and choros- place) meta- change; transformation; following something in a series (from the Greek meta- change) mito- thread (from the Greek mitos- a thread) mono- one; single; alone (from the Greek monos- alone) nucleus kernel (from the Latin nux- nut) poly- many (from the Greek polys- many) pro- before; for; in front of (from the Greek and Latin pro- for or before) some body (from the Greek soma- body) sub under; beneath; below (from the Latin sub- below) tel- end (from the Greek telos- ultimate end) tetra- four (from the Greek tettares- four) tri- three (from the Greek tri- three) zygote diploid cell created by fertilization (from the Greek zygotes- yoked) CHAPTER 12: PATTERNS OF INHERITANCE WHERE DOES IT ALL FIT IN? Chapter 12 applies the information on meiosis covered in Chapter 11 to the principles of classical inheritance. Students are likely to have many misconceptions about inheritance patterns and they usually do not connect meiosis to inheritance. It is important to reinforce to students the goals and outcomes of meiosis before starting this chapter. Chapter 12 will serve as an important reference for Chapter 13. SYNOPSIS • • Early geneticists believed that genetic material from each parent blended in the offspring and that variability was not introduced from outside the species. Blending and lack of variability, though, should result in individuals that greatly resemble rather than differ from one another. This paradox was partly solved by early plant breeders who found that hybrids differed greatly from their parents and often from one another. They reported that certain physical traits disappeared for a generation and reappeared in the next. Gregor Mendel cross-bred seven well-¬documented varieties of a pea. Most importantly, he quantified his experiments, meticulously counted seeds of hundreds of crosses and grouped them by apparent physical traits. Mendelian genetics is derived from the mathematical ratios that describe the segregation and assortment of hereditary material. • Mendel’s model states that each parent transmits a set of information about its traits in its gametes. Therefore, each individual possesses two factors (genes) for each trait. Each factor exhibits many possible forms (alleles) that do not influence one another; each remains discrete within the cell. An individual may be homozygous and possess two identical alleles, or heterozygous and have two different alleles. The presence of a factor does not ensure its expression; dominant traits are expressed while recessive traits are generally not expressed. The existence of the recessive allele in a heterozygote causes that factor to be masked for a generation. Additionally, there is a difference between an individual’s phenotype, or overall appearance, and its genotype, its precise genetic blueprint. Mendel’s First Law of Heredity explains how alleles randomly segregate in the gametes, each gamete has an equal chance of receiving either allele. His second law explains that different alleles assort into gametes independently of one another, the presence of an allele of one trait does not preclude the presence or absence of any other allele of any other trait. • LEARNING OUTCOMES 12.1 Experiments Carried Out by Mendel Explain Heredity 1. Describe the early experiments in plant hybridization. 2. Explain the advantages of the garden pea for breeding experiments. 3. Contrast Mendel’s experimental design with the earlier studies of T.A. Knight. 12.2 Mendel’s Principle of Segregation Accounts for 3:1 Phenotypic Ratios 1. Illustrate a monohybrid cross through the F2 generation. 2. Explain the Principle of Segregation. 3. Explain the basis of the 3:1 Mendelian ratio using a Punnett square. 12.3 Mendel’s Principle of Independent Assortment Asserts That Genes Segregate Independently 1. Using a Punnett square, explain the genetic basis of a 9:3:3:1 dihybrid ratio. 12.4 Probability Allows Us to Predict the Results of Crosses 1. Apply the rule of addition and the rule of multiplication to genetic crosses. 2. Explain the outcome of a monohybrid testcross. 12.5 Genotype Dictates Phenotype by Specifying Protein Sequences 1. Explain how genotype determines phenotype. 12.6 Extending Mendel’s Model Provides a Clearer View of Genetics in Action 1. Provide a genetic explanation of continuous variation. 2. Explain the genetic basis of pleotropic influences on inheritance. 3. Estimate the maximum number of alleles a gene may possess, and explain your estimate. 4. Explain how to distinguish between lack of dominance and incomplete dominance. 5. Explain how the environment might act to alter observed Mendelian ratios. 6. Explain the genetic basis of a dihybrid phenotypic ratio of 9:7. COMMON STUDENT MISCONCEPTIONS There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 12 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature. • Students believe that sexual reproduction is merely for increasing populations • Students have trouble connecting the events of meiosis with germ cell formation • Students have trouble connecting the events of meiosis with patterns of inheritance • Students think that traits skip generations • Students do understand that a Punnett square represents offspring probabilities • Students believe that gender in all organisms is determined by X and Y chromosomes • Students confuse the roles of autosomes and sex chromosomes • Students do not associate gene expression with inherited characteristics • Students believe sexual reproduction always involves mating • Students do not understand other mechanisms of sexual reproduction besides mammalian reproduction • Students do not fully understand the role of genetics and environment on determining observable variation in organisms • Students believe acquired characteristics can be inherited • Students think that all genetic disorders are homozygous recessive • Students believe that inbreeding causes genetic defects • Students do not take into account the role of crossing over in classical inheritance variation • Students believe that chromosomes are segregated into gametes that contain either a pure maternal or pure paternal homologous sets INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE • Mendelian genetics is one of the classic discussions in introductory biology. Most students are introduced to this in high school, but few really understand what is meant by segregation and independent assortment. Segregation of alleles is hard to visualize without a good understanding of meiosis. One can truly respect Mendel’s scientific ability when realizing that neither chromosomes nor meiosis had been discovered yet. • The most frequent mistake a beginner makes in calculating a dihybrid cross is putting the two alleles for the same trait in a single gamete. Make them separate (segregate) those letters! A normal gamete can have only one of each allele. • There is a lot of new terminology associated with genetics. Homozygous and heterozygous are frequently confused as are phenotype and genotype and, for some strange reason, allele and locus. Again, understanding the meanings of prefixes, suffixes, and root words helps enormously. A background in a romance language has enormous benefits. • Many of your students are medical-school bound and relate to the topic of this chapter because they see its direct application to their futures. Examining one’s own genetic background is to some extent health-oriented fortune telling. By studying the ailments of one’s parents, grandparents, and other relatives, a picture of one’s own future begins to develop. Most serious diseases are not under strict genetic control, but research indicates a strong genetic component in many, including cancer and heart disease. HIGHER LEVEL ASSESSMENT Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 11. Application • Have students predict a monohybrid cross Punnett square for a simple trait in their family. • Have students explain why a family who had four female children in a role have an equal chance of having a boy or a girl as the next child. • Ask students to explain the relationship between meiosis and the assignment of alleles in a Punnett square. Analysis • Ask students to hypothesize why inbreeding populations are likely to have an abundance or a lack of genetic disorders. • Ask students to explain the effects of a 4N complement of DNA on the expression of traits. • Ask students to explain why certain characteristics appear very rarely in a population of organisms. Synthesis • Ask students to come up with a reason why gender in alligators does not follow the predicted Mendelian pattern of inheritance. • Have students explain why a certain dominant characteristic only appears in male offspring of an organism and does not show up in females. • Ask students to explain how the child of a father with type AB blood and a mother with type O blood was born with type O blood. Evaluation • Ask students to evaluate the benefits of drugs claiming to slow down the genetic progression of aging. • Ask students to discuss the pros and cons of inbreeding crops and agricultural animals. • Ask students to evaluate the impact of crossing over during meiosis on polygenic traits. VISUAL RESOURCES • Many different kinds of apparatus are available to illustrate Mendelian genetics, including modeling clay and pop-it beads. Several very sophisticated bead kits are sold through biological supply houses; unfortunately, most are too small to be useful in a class larger than twenty-five students. • • Much of the visual material is better handled in the lab, after initial exposure to the basics in the lecture. Try to keep the genetics-oriented lab instructors from showing too many of their own short-cuts. Have them stick to the old Punnett square. Students that derive short cuts on their own may gain a better understanding of the material. • IN-CLASS CONCEPTUAL DEMONSTRATIONS A. Animated Karyotype Introduction This fun and fast demonstration engages students in developing a human karyotype. The click and drag animation allows the instructor to interact with students while selecting chromosomes to build a karyotype diagram. Materials • Computer with live access to Internet • LCD projector attached to computer • Web browser with bookmark to Karyotype Animation at: http://www.gla.ac.uk/medicalgenetics/nhs/karyotypemovie.htm Procedure & Inquiry 1. Introduce the concept of karyotyping 2. Pull up the Karyotype Animation website 3. Touch the cursor to a chromosome and watch where it ends up on the karyotype diagram 4. See if the students can match it with the homologous chromosome 5. Repeat several times until the diagram is complete 6. Ask the students to describe the features used to match up the pairs of homologous chromosomes B. Virtual Punnett Practice Introduction This demonstration uses an on-line animated Punnett square to review the calculation of offspring probabilities. It immediately draws the Punnett squares for monohybrid and dihybrid crosses. In addition, it gives the offspring probability ratios. The animation is useful for in-class formative evaluation of Mendelian inheritance. Materials • Computer with live access to Internet • LCD projector attached to computer • Web browser with bookmark to Punnett Square Calculator at: http://www.changbioscience.com/genetics/punnett.html • Sheets of writing paper for students Procedure & Inquiry 1. Introduce the topic of meiosis and how it is related to Punnett squares. 2. Pull up the Punnett Square Calculator 3. Pick a simple monohybrid cross from the drop-down windows 4. Ask the students to write the Punnett square for the cross 5. Then show the cross 6. Repeat this with several crosses while questioning and surveying students about their answers LABORATORY IDEAS The mathematical calculation of Mendelian offspring probabilities is best reinforced when students are able to see the outcomes of genetic crossing. This activity uses genetic corn as a model for investigating the probabilities of various dihybrid crossing. a. Provide a group of students with the following materials without tell them anything about the genetic nature of the corn ears: a. Ear of pure smooth yellow corn b. Ear of pure yellow wrinkly corn c. Ear of heterozygous X heterozygous corn cross - purple/yellow: smooth/wrinkled d. 4 X 4 Punnett square diagram as shown below: b. First ask the students to explain the differences between the three ears of corn. c. Have students discuss which corn is typical of edible corn and whether that is the natural characteristics that would be found in a large population of corn left to grow in the wild. d. Instruct the students to use the Punnett square to calculate the offspring probabilities of breeding two corn parents heterozygous for kernel color and shape. Provide students with the following information: a. Purple - P (dominant) b. Yellow - p (recessive) c. Smooth - S (dominant) d. Wrinkly - s (recessive) They should calculate a 9:3:3:1 ratio e. Now tell the students if they believe the purple/yellow corn has a 9:3:3:1. f. Ask them how they would determine this using the corn given to them. g. Direct the students to count the different types of kernels on the purple/yellow corn. They should be questioned to see if they recognize the four different types of kernels h. Have the students determine how close they came to a 9:3:3:1 ratio from counting kernels on the purple/yellow ear of corn. They should record their information on a table such as provided below: Phenotype: _______ ______ _______ _______ Number: _______ _______ _______ _______ Ratio: ______ : ______ : ______ : ______ i. Have the students hypothesize the genotypes of the yellow smooth and yellow wrinkly corn. Ask them which corn will always produce pure lineages of offspring that resemble the parents. Also ask the students how the corn sold in groceries stores is bred to have its characteristics. LEARNING THROUGH SERVICE Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course. 1. Have students present a forum on the benefits and risks of monoculture to a civic group. 2. Have students design an educational animated PowerPoint presentation about Mendelian genetics for middle school teachers. 3. Have students tutor middle school or high school biology students studying classical genetics. 4. Have students present a talk to elementary students about the inheritance of genetic disorders. ETYMOLOGY OF KEY TERMS di- two; twice (from the Greek di- two) bi- two (from the Latin bi- two) hetero- different (from the Greek heteros- the other of two) homeo- likeness; resemblance; similarity (from the Greek homoios- like) • extra- outside; beyond (from the Latin exter- being on the outside) mono- one; single; alone (from the Greek monos- alone) • phenotype observable traits (from the Greek phainein- to show and typos type Instructor Manual for Understanding Biology Kenneth Mason, George Johnson, Jonathan Losos, Susan Singer 9780073532295, 9781259592416
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