Lecture 19: Mitosis, Meiosis and Life Cycles

1. Distinguish between mitosis and meiosis in a manner that makes it clear that you know what each is and how they differ.

2. Compare the length of the meiotic prophase in human males and females. Which more closely resembles mitotic prophase. How do both differ from mitotic prophase? (See page 332 of the textbook if you have difficulty with this question).

3. Briefly summarize the major events in a haploid-diploid life cycle. Identify a species with a predominantly haploid life cycle and a species with a predominantly diploid life cycle.

4. What abbreviations are used to designate the four parts of the mitotic cell cycle and what does each stand for?

5. Distinguish between karyokinesis and cytokinesis in a manner that makes it clear that you know what each is and how they differ.

6. Name and briefly describe the four stages that mitosis is commonly divided into. (Caution, this is not a repeat of question 4).

7. Describe two distinctly different processes that occur during meiosis to bring about mixing of the two parental genotypes during formation of gametes. Identify the stage of meiosis at which each occurs as precisely as you can, and briefly describe the mechanisms that are involved.

8. Identify the five stages of meiotic prophase and briefly describe each, including important genetic events that are occurring during that phase.

9. What role does mitosis play in a sexual life cycle? (Why do sexually reproducing organisms need mitosis at all?)

10. At what stage of meiosis does crossing over (genetic recombination) occur? (see page 331 of textbook if you are uncertain).

11. What are chiasmata and what is their genetic significance?

12. At what stage of meiosis is independent assortment of unlinked genes achieved? What is the mechanism that is involved?

13. At what stage during meiosis do the centromeres of the individual sister chromatids separate?

14. At what stage of meiosis is the chromosome number reduced to haploid (bivalents with sister chromatids still paired count as single chromosomes).

15. At what stage of meiosis is the DNA content per gamete reduced to haploid?

16. In terms of genetic uniformity of the ultimate products of each process, how do mitosis and meiosis differ?

17. What is a lampbrush chromosome and under what circumstances is it observed?

18 Briefly define each of the folowing and explain its genetic significance or its significance to the study of genetics.

a. Homologous chromosomes.
b. Tetrad.
c. Synaptonemal complex
d. Biparental inheritance.
e. Gametophyte.

19. What are the consequences of nondisjunction during one or the other of the meiotic divisions?

20. A human female has 23 pairs of chromosomes. Assuming that the members of each pair differ from each other, how many different different gametes does she have the potential ability to generate, based on independent assortment alone?

21. Meiosis in a female generates one ovum and 3 polar bodies, whereas in a male meiosis generates 4 spermatozoa. Does this result in four times as much genetic diversity in male gametes as in female gametes? Explain the reasoning behind your answer.

22. The part of the mitotic cell cycle that was originally viewed simply as "interphase" is now viewed quite differently.

a. How was interphase defined and what criteria were used to define it?
b. Identify the three parts that interphase is now divided into and explain the original significance of each of the three parts.
c. How has modern research changed our view of the first and third segments of "interphase"?

23. Meiosis generates genetic diversity, whereas mitosis maintains genetic constancy. Explain how this is advantageous to the organism.

24. There is evidence that transcription continues in oogenesis, even after meiotic prophase has begun.

a. What is the evidence for transcription during meiotic prophase?
b. Speculate on what biological purpose such transcription serves.