MCAT Question A Day - 3/24/14 - Answer!
Individuals with Turner’s syndrome have 45 chromosomes (one sex chromosome is missing in the cells of these “XO” individuals). This usually is caused by meiotic nondisjunction during gametogenesis. Which statement is not correct concerning people with this disorder?
A. They are genetic females.
B. They are subject to sex-linked disorders at frequencies similar to those predicted for normal females.
C. The nondisjunction event could have occurred during meiosis in either the male or female parent.
D. If meiosis occurs in Turner’s syndrome individuals, one daughter cell resulting from the first meiotic division will have no sex chromosome.
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The correct answer is (B). A familiarity with the events of meiosis and the factors that influence sex determination are helpful, but a clear understanding about the pattern of inheritance for sex-linked traits is essential. Since normal females have two X chromosomes, Turner’s syndrome females (XO) do not have the same probabilities of inheriting sex-linked disorders (they actually have the same chances as males).
