Question

Consider a human germ cell undergoing normal meiosis (with only chromosome 23 shown). The dark blue represents the maternal chromosome and the light blue represents the paternal chromosome. Which of the 6 possible gamete types would you observe following the completion of meiosis (Choose all that apply)? 3. Consider the same human germ cell. If a single chromosome nondisjunction event occurs during meiosis I, which gamete types will you expect following the completion of meiosis (Choose all that apply)? 4. Consider the same human germ cell. If a single chromosome nondisjunction event occurs during meiosis II, which gamete types might you expect following the completion of meiosis (Note: There are two possible answers depending on which of the two cells that are created by Meiosis I are subject to chromosome nondisjunction - choose all that apply for one possibility only)? oooo

Answer 1

2. C and F. Explanation- Initially the cell is diploid having 2n=2. Thus, the gametes which are formed will be haploid having n=1. This means that the gametes will have one chromosome in case of normal meiosis.

3. A and D. Explanation- Nondisjunction at meiosis I results in 4 gametes having n+1, n+1, n-1, n-1 chromosomes. So, two gametes will have 1+1= 2 chromosome 23 whereas the other two gametes will have 1-1=0 chromosome 23. The gametes having 2 chromosomes will have both paternal and maternal chromosomes.

4. C and E. Explanation- Nondisjunction in dark blue chromosome at meiosis II results in 4 gametes having n, n, n+1, n-1 chromosomes. So two gametes will have 1 chromosome. Third gamete will have 2 copies of chromosome 23 and fourth gamete won't have any copy of chromosome 23. The gamete having 2 chromosomes will have only dark blue (maternal) chromosomes.