This pedigree supports the fact that polydactyly is due to a dominant allele, be

Question

This pedigree supports the fact that polydactyly is due to a dominant allele, because if it were due to a recessive allele and both parents show the recessive phenotype, then ____.

a. All of the sons and none of the daughters would have polydactyly

b. All of the daughters and none of the sons would have polydactyly

c. All of the offspring would have polydactyly

d. None of the sons would have polydactyly

e. None of the daughters would have polydactyly

Polydactyly is a genetic condition in which a person has more than 5 fingers per hand or 5 toes per foot. The pedigree here shows 3 generations of a family. Notice that some individuals (shown in black) have polydactyly. Represent the dominant allele as A & the recessive as a. Use this information & the pedigree below to answer the next 4 questions. S0 10 12 13 14

Explanation / Answer

Any of the offspring would have polydactyly

The chances vary based on each person's family history. Sometimes extra digits appear to be a strong family trait that does not usually skip generations. In this case, we would consider the gene change to be dominant, so the chance of passing the polydactyly trait on to a child is 50 percent with each pregnancy if one parent has polydactyly. Alternatively a gene change might be recessive, in which case the chance of a person with polydactyly passing that trait onto a child is much smaller, depending on their partner's family history.

When polydactyly does occur as a family trait, it may occur in different combinations. One family member may have extra digits only on their hands, while another family member may have extra digits only on their feet.

Polydactyly can also occur even if there is no family history of extra digits.

There are special exceptions to these rules. Genetic counseling is recommended to understand how these exceptions may apply to your family.

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