Holoprosencephaly Is a Highly Variable Condition in Mammals, Including Humans

question 27

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 Shh mutations. Familial cases are inherited as dominants. Which of the following do you expect?

• A)HPE3 is actually a multigene complex.
• B)Each type of malformation is due to a different HPE3 allele.
• C)HPE3 expression is modified by genetic background.
• D)HPE3 individuals also share a common environmental exposure.
• E)All mutations in Shh that result in HPE3 are due to frameshifts.

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Definitions:

Arrector Pili

Small muscles attached to hair follicles in mammals; their contraction causes hair to stand up, known as "goosebumps."

Voluntary Control

The conscious regulation of skeletal muscles and movements by the brain, permitting actions like walking, speaking, and grabbing.

Nervous Tissue

Specialized tissue that makes up the central and peripheral nervous systems, consisting of neurons and supporting cells, responsible for transmitting nerve signals.

Neurons

Nerve cells that are the building blocks of the nervous system, involved in processing and transmitting information through electrical and chemical signals.