9. Mitosis and Meiosis

In which step of prophase I does crossing-over occur?

Are the two daughter cells produced from meiosis I diploid or haploid?

Are the four daughter cells produced from meiosis II diploid or haploid?

Which of the following are sources of genetic variation during meiosis?

During which stage of meiosis do sister chromatids separate?

Our closest primate relative, the chimpanzee, has a diploid number of 2n =48. For each of the following stages of M phase, identify the number of chromosomes present in each cell.

early prophase I

Our closest primate relative, the chimpanzee, has a diploid number of 2n =48. For each of the following stages of M phase, identify the number of chromosomes present in each cell.

end of meiotic anaphase II

Our closest primate relative, the chimpanzee, has a diploid number of 2n =48. For each of the following stages of M phase, identify the number of chromosomes present in each cell.

meiotic metaphase I

Cohesion between sister chromatids, as well as tension created by the pull of kinetochore microtubules, is essential to ensure efficient separation of chromatids at mitotic anaphase or in meiotic anaphase II. Explain why sister chromatid cohesion is important, and discuss the role of the proteins cohesin and separase in sister chromatid separation.

The diploid number of the hypothetical animal Geneticus introductus is 2n = 36. Each diploid nucleus contains 3 ng of DNA in G₁.

Explain why a somatic cell of Geneticus introductus has the same number of chromosomes and the same amount of DNA at the beginning of mitotic prophase as one of these cells does at the beginning of prophase I of meiosis.

The diploid number of the hypothetical animal Geneticus introductus is 2n = 36. Each diploid nucleus contains 3 ng of DNA in G₁.

What amount of DNA is contained in each nucleus at the end of S phase?

Explain how the behavior of homologous chromosomes in meiosis parallels Mendel's law of segregation for autosomal alleles D and d. During which stage of M phase do these two alleles segregate from one another?

Suppose crossover occurs between the homologous chromosomes in the previous problem. At what stage of M phase do alleles D and d segregate?