One of two major forms of a human condition called neurofibromatosis (NF1) is inherited as a dominant gene, although it may range from mildly to very severely expressed. Which of the following is the best explanation for why a young, affected child is the first in her family to be diagnosed?
A) The mother carries the gene but does not express it.
B) One of the parents has a mild expression of the gene.
C) The condition skipped a generation in the family.
D) The child has one more chromosome than either of the parents.

Question

Quizplus · Accepted Answer

Neurofibromatosis (NF1) is inherited as a dominant gene, which means that only one copy of the gene is enough to show the condition. If one of the parents has a mild expression of the gene, it is possible that they may not have recognized their symptoms or been diagnosed with the condition. In this case, their child may be the first in the family to be diagnosed as the condition became more severe. The other options (A, C, and D) do not provide a plausible explanation for why the child is the first in the family to be diagnosed.

One of Two Major Forms of a Human Condition Called