Holoprosencephaly is a highly variable condition in mammals, including humans. Its effects range from an absence of brain areas, mid- face disorders, and cyclopia to slight dental abnormalities. One form, HPE3, is caused by null mutations in Shh. Familial cases are inherited as a dominant trait. Which of the following do you expect?
A) HPE3 individuals also share a common environmental exposure.
B) HPE3 expression is modified by genetic background.
C) All mutations in Shh that result in HPE3 are due to frameshifts.
D) HPE3 is actually a multigene complex.
E) Each type of malformation is due to a different HPE3 allele.

Question

Quizplus · Accepted Answer

HPE3 expression can be influenced by the genetic background of the individual, which can modify the severity and type of symptoms experienced. This accounts for the variability in the condition's presentation among different individuals.

Holoprosencephaly Is a Highly Variable Condition in Mammals, Including Humans