ATARnotes trial exam 1 Biology, MC, q23
Which of the following characteristics of a monogenic trait proves that a condition is NOT X-linked dominant?
B. The mother does not have the condition, yet the son does
C. The father has the condition, yet the daughter does not
The answer says its B, but C is arguably just as valid, if not more so. The answer does not justify why C is wrong, just why B is correct). All daughters of an affected male will show the trait as they have to inherit his chromosome. If a mother does not express the condition, isn't it possible for the condition to be relevant to a small number of cells? Thus, although very improbable, isn't it possible for all of the X chromosomes in all of these relevant cells that carry the dominant allele to be inactivated, resulting in a phenotypically normal mother who is still capable of passing on an X chromosome with the dominant allele to her child.
Thanks in advance guys!
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