Question

Red-green color blindness is caused by a mutation in a gene on the X chromosome. X^a is the recessive mutant allele that causes color blindness; X^A is the dominant, functional allele. You meet a patient who has Klinefelter syndrome (that is, he has an XXY karyotype). His mother is color blind, but his father has normal color vision. Your patient has both the X^A and the X^a alleles.

1. You hypothesize that your patient’s syndrome is due to a meiotic nondisjunction event that occurred in: (circle the correct options) (2 pts)

this patient                this patient’s father              this patient’s mother

                                                Meiosis I         or        Meiosis II

2. In the space provided below, illustrate how the meiotic nondisjunction event occurred, showing only the sex chromosomes. If you think it could happen in either meiosis I or II, pick one of these for illustration. (6 pts)

1. Use the symbols below to illustrate the X and Y chromosomes:
2. Use arrow(s) to indicate the cell(s) that could give rise to your patient’s abnormal karyotype.

3. You also find a small number of cells in this patient with only one X and one Y chromosome. Explain this phenomenon in no more than two sentences. Be specific about in which individual and roughly when this relevant event might have taken place. (2 pts)

Answer 1