August 5, 2012
According to the pedigree, is cystic fibrosis inherited as a dominant or as a recessive trait?
Explain how you made your conclusion using evidence from the pedigree and the principles
According to the pedigree cystic fibrosis is passed from generation to generation as a
recessive trait because it skips generations. This conclusion was reached because no one
from Generation I was affected with the disease. However, in Generation II the first male
was unaffected with the disease, but the second male was infected with the disease. This
proves that it is passed as a recessive trait rather than a dominant trait. This is possible
when both parents are hybrids for the trait; which means that they do not have the disease,
but carry the gene. Children of two hybrid parents can inherit a recessive gene from each
parent. Two recessive genes shows the cystic fibrosis disease.
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