Chapter 15, Problem 17TYK

Some girls who fail to undergo puberty are found to have Swyer syndrome, a condition in which they are externally female but have an XY genotype. Which of the following statements may explain the origin of this syndrome?

1. a. A mutation in the XIST gene, which codes for RNA molecules that coat the X chromosome and initiate X-inactivation, must have occurred.
2. b. A nondisjunction in the egg from the mother resulted in both sex chromosomes coming from the father. Genomic imprinting of the father’s X chromosome then caused the development of a female phenotype.
3. c. These individuals are actually XXY; the second X is not seen because it is condensed into a Barr body. They have small testes and are sterile but otherwise appear female.
4. d. A mutation or deletion of the SRY gene on the Y chromosome prevented development of testes and production of the male sex hormones required for a male phenotype.