Consider an autosomal dominant trait/condition. If an unaffected parent and an affected heterozygous parent are pregnancy, what is the chance of their having an unaffected child?
50%
Correct! Examine a Punnett square with these paternal alleles and you can see the risk for transmitting the condition with each pregnancy is 50%.
Two phenotypically normal individuals have an affected child. What is the most likely conclusion about the parents? (No other family members are affected)
They both carried the disease allele.
Correct! In this case, the most likely explanation is that this is an autosomal recessive condition and that both parents are carriers.
They are not the parents of the child.
Incorrect
They are affected.
Incorrect
No conclusion can be drawn.
Incorrect
Cystic fibrosis is autosomal recessive. This means that:
Both sexes can be affected and can “skip” generations through carriers.
Correct! Autosomal recessive conditions affect both sexes equally may not be seen in every generation because carriers do not express the condition.
Carrier mothers pass the mutations to some of their sons, but not to their daughters.
Incorrect
Each affected individual has at least one affected parent
Incorrect
Both sexes are affected because new mutations occur frequently
Incorrect
Several members of the Fitzsimmons family have polydactyly, and they differ in their numbers of extra fingers and toes. Yet, certain relatives who should have extra digits don’t, such as Megan Fitzsimmons. She has two children, a son with two extra fingers and a daughter with an extra toe, and her father has an extra digit on each hand and foot. Polydactaly in this family is:
Invariably expressive and incompletely penetrant.
Incorrect
Variably expressive and incompletely penetrant.
Correct! Incomplete penetrance is seen with Megan who has no polydactyly and variable expressivity is seen with the different levels of severity family members experience this condition.
Pleiotropic and a phenocopy
Incorrect
Dominant and recessive
Incorrect