BackCohesion 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 the 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?
Define and discuss these terms:
(a) synapsis
(b) bivalents
(c) chiasmata
(d) crossing over
(e) chromomeres
(f) sister chromatids
(g) tetrads
(h) dyad
(i) monads
A woman who sought genetic counseling is found to be heterozygous for a chromosomal rearrangement between the second and third chromosomes. Her chromosomes, compared to those in a normal karyotype, are diagrammed to the right.
Using a drawing, demonstrate how these chromosomes would pair during meiosis. Be sure to label the different segments of the chromosomes.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., Am and Ap). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.
Draw all possible combinations of chromatids during the early phases of anaphase in meiosis II.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., Am and Ap). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.
Assume that during meiosis I none of the C chromosomes disjoin at metaphase, but they separate into dyads (instead of monads) during meiosis II. How would this change the alignments that you constructed during the anaphase stages in meiosis I and II? Draw them.
Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., Am and Ap). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.
Assume that each gamete resulting from Problem 29 fuses, in fertilization, with a normal haploid gamete. What combinations will result? What percentage of zygotes will be diploid, containing one paternal and one maternal member of each chromosome pair?