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Name Date

AP: CHAPTER 13

MEISOSIS AND SEXUAL LIFE CYCLES 1. define the following terms. a. Gametes b. Somatic cells c. Karyotype d. Homologous chromosomes e. Alternation of generations f. Meiosis I g. Meiosis II 2. Why is meiosis called a “reduction division”? Why is this process necessary for sexual reproduction? 3. Explain synapsis.

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4. Label the diagram of the human lifecycle. Include the chromosome numbers at each stage. 5. Use the diagrams below to distinguish mitosis from meiosis. For an organism where 2n=4, draw a cell at metaphase of mitosis and a cell at metaphase 1 of meiosis. Metaphase of mitosis Metaphase 1 of meiosis 6. Meiosis is said to be a double division. Explain.

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7. Draw a pair of homologous chromosomes in synapsis and then illustrate a crossing over event and the products of crossing over. Label the chiasmata. 8. At what stage of meiosis does crossing over occur? 9. Compare the products of mitosis and meiosis. a. Mitosis b. Meiosis 10. Complete the table by writing yes or no to distinguish meiosis from mitosis. Event Meiosis Mitosis

One division

Two successive divisions

Daughter chromosomes separate

Homologous chromosomes (homologues) separate

Daughter cell with the diploid number of chromosomes

Daughter cells with the haploid number of chromosomes

Somatic cells

Formation of gametes

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11. Meiosis is an important source of variation. Define and describe how each of the following contributes to variation within species. a. independent assortment b. crossing over c. random fertilization 12. What is the significance of genetic variation to natural selection and evolution? 13. What is a karyotype? 14. Identify several things that can be seen with a karyotype. 15. The following diagram represents some of the stages of meiosis (not in the right order). Label these stages. a. b. c. d. e. f. Now place these stages in the proper sequence.

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d.

a.

16. Label the following diagram to review the terms that describe replicated chromosomes in a diploid cell. 17. What is the overall purpose of meiosis? 18. In what type of organism(s) and cells does meiosis occur? What are the stages of meiosis? 19. The fruit fly, Drosophila melanogaster, has a total of eight chromosomes (four pairs) in each of its somatic cell. Keep in mind that the stages of cell division were first recognized from an examination of fixed slides of tissues undergoing division. On fixed slides, cells are captured or frozen at particular points in the division cycle. Using these static slides, early microscopists identified specific arrangements or patterns of chromosomes that occurred at various stages of the cycle and gave these stages names (interphase, prophase I, and so on). Later work using time-lapse photography made it clear that meiosis is a continuous process. Once division begins, the chromosomes move fluidly from one phase to the next. Assume you are a microscopist viewing fruit fly cells that are undergoing meiosis. Within each of the circles (which represent cell membranes) on the next pages, draw what you would expect to see if you were looking at a cell in the stage of meiosis indicated. If no circle is present, draw what you would expect to see at the given stage.

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Prophase I Metaphase I Anaphase I Telophase I Cytokinesis Daughter cells

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Prophase II Metaphase II Anaphase II Telophase II Cytokinesis Daughter cells

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20. Six centromeres are observed in a prophase I cell from another species of insect.

a. How many pairs of chromosomes does this organism contain? b. For each stage of meiosis, indicate the number of centromeres you would expect to find and the number of copies of chromosomes attached to each centromere. Stages of meiosis: Number of centromeres visible

per cell Number of chromosome copies attached to each centromere

Anaphase I

Prophase II