Holoprosencephaly Is a Highly Variable Condition in Mammals, Including Humans

question 53

Multiple Choice

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.

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