Meiosis and Sexual Reproduction

1. Meiosis and Sexual Reproduction Chapter 10

2. Meiosis—type of nuclear division that occurs as part of sexual reproduction. • Haploid (n) number—cell condition in which one of each type of chromosome is present; half the diploid number. • Diploid (2n) number—cell condition in which two of each type of chromosome are present.

3. Homologous Pairs of Chromosomes • Member of a pair of chromosomes that are alike and come together in synapsis • Occurs during prophase of first meiotic division. • One member of a homologous pair was inherited from the male parent and the other is inherited from the female parent.

4. Meiosis Overview • Meiosis I • Homologous chromosomes separate. • Daughter cells have one copy of each kind of chromosome in various combinations. • No replication of DNA is needed between meiosis I and meiosis II.

5. Meiosis Overview • Meiosis II • Four haploid daughter cells • Each chromosome consists of one chromatid. • Daughter cells mature into gametes; sperm or eggs.

6. Genetic Recombination • Process in which new genetic information is incorporated into a chromosome or DNA fragment.

7. Genetic Recombination • Crossing-over—is an exchange of genetic material between nonsister chromatids of a bivalent during meiosis I. • Bivalent—homologous chromosomes, each having sister chromatids that are joined by a nucleoprotein lattice during meiosis.

8. Genetic Recombination • Independent assortment—homologous chromosomes separate independently or in a random manner. 4 possible orientation of homologous pairs at metaphase plate

9. Genetic Recombination • Fertilization—fusion of sperm and egg nuclei, producing a zygote that develops into a new individual.

10. A bivalent is • A homologous chromosome • The paired homologous chromosomes. • A duplicated chromosome composed of sister chromatids. • The two daughter cells after meiosis I.

11. Crossing over occurs between • Sister chromatids of the same chromosome. • Two different kinds of bivalents. • Two different kinds of chromosomes. • Nonsister chromatids of a bivalent. • Two daughter nuclei.

12. Fertilization • Is a source of variation during sexual reproduction. • Is fusion of the gametes • Occurs in both animal and plant life cycles. • Restores the diploid number of chromosomes. • All of these are correct.

13. Phases of Meiosis • Prophase I • Spindle fibers form as the centrosomes move away from one another. • Nucleolus disappears. • Homologous chromosomes pair during synapsis. • Crossing-over may occur at this time.

14. Phases of Meiosis • Metaphase I • Fully formed spindle fibers. • Alignment of the homologous chromosomes at the metaphase plate.

15. Phases of Meiosis • Anaphase I • Homologous chromosomes separate and move to opposite poles. • Each chromosome still consist of 2 chromatids.

16. Phases of Meiosis • Telophase • Nuclear envelops re-form and nucleoli appear. • Each daughter cell has one chromosome from each pair of homologous pair.

17. Phases of Meiosis • Interkinesis • Similar to interphase between mitotic division. • Except DNA replication does not occur. • Chromosomes are already duplicated.

18. Phases of Meiosis • Prophase II • Cells have one chromosomes from each homologous pair.

19. Phases of Meiosis • Metaphase II • Chromosomes align at the metaphase plate.

20. Phases of Meiosis • Anaphase II • Sister chromatids separate. • Daughter chromosomes move toward the poles.

21. Phases of Meiosis • Telophase II • Spindle fibers disappear. • Nuclei form. • Cytokinesis takes place.

22. Phases of Meiosis • Daughter cells • Meiosis I • Form 2 daughter cells. • Diploid number of chromosomes. • Meiosis II • From 4 daughter cells • Haploid number of chromosomes.

23. Comparison • Meiosis I • Prophase I—pairing of homologous chromosomes • Metaphase—homologous chromosomes align at the metaphase plate. • Mitosis • Prophase—no pairing of chromosomes. • Metaphase—duplicated chromosomes at metaphase plate

24. Comparison • Meiosis I • Anaphase I—homologous chromosome pairs separate and move to separate poles. • Telophase I—two haploid daughter cells. • Mitosis • Anaphase—sister chromatids separate, becoming daughter chromosomes that move to the poles. • Telophase—two daughter cells, identical to the parent cell.

25. Comparison • Meiosis II • Prophase II—no pairing of chromosomes. • Metaphase II—haploid number of duplicated chromosomes at metaphase plate. • Mitosis • Prophase—no pairing of chromosomes. • Metaphase—duplicated chromosomes at metaphase plate

26. Comparison • Meiosis II • Anaphase II—sister chromatids separate, becoming daughter chromosomes that move to the poles. • Telophase—four haploid daughter cells, no genetically identical. • Mitosis • Anaphase—sister chromatids separate, becoming daughter chromosomes that move to the poles. • Telophase—two daughter cells, identical to the parent cell.

27. If a parent cell has twelve chromosomes, then each of the daughter cells following meiosis will have… • Forty-eight chromosomes • Twenty-four chromosomes • Twelve chromosomes • Six chromosomes • Any one of these could be correct.

28. At the metaphase plate during metaphase I of meiosis, there are • Chromosomes consisting of one chromatid. • Unpaired duplicated chromosomes. • Bivalents. • Homologous pairs of chromosomes. • Both c and d are correct.

29. At the metaphase plate during metaphase II of meiosis, there are • Chromosomes consisting of one chromatid. • Unpaired duplicated chromosomes. • Bivalents • Homologous pairs of chromosomes. • Both c and d are correct.

30. During which phase of meiosis do homologous chromosomes separate? • Prophase II • Telophase I • Metaphase I • Anaphase I • Anaphase II

31. During which phase of meiosis do homologous chromosome pairs separate? • Prophase II • Telophase I • Metaphase I • Anaphase I • Anaphase II