1. At a certain locus, a person has two alleles, A and a.

a. What alleles will be present in this person’s gametes?

b. When do A and a segregate (1) if there is no crossing over between the locus and the centromere of the chromosome? (2) if there is a single crossover between the locus and the centromere?

2. What is the main cause of numerical chromosome abnormalities in humans?

3. Disregarding crossing over, which increases the amount of genetic variability, estimate the probability that all your chromosomes have come to you from your father’s mother and your mother’s mother. Would you be male or female?

4. A chromosome entering meiosis is composed of two sister chromatids, each of which is a single DNA molecule.

a. In our species, at the end of meiosis I, how many chromosomes are there per cell? How many chromatids?

b. At the end of meiosis II, how many chromosomes are there per cell? How many chromatids?

c. When is the diploid chromosome number restored? When is the two-chromatid structure of a typical metaphase chromosome restored?

5. From Figure 2-7, estimate the number of genes per million base pairs on chromosomes 1, 13, 18, 19, 21, and 22. Would a chromosome abnormality of equal size on chromosome 18 or 19 be expected to have greater clinical impact? On chromosome 21 or 22?