Cystic fibrosis is caused by the allele f, which is completely recessive to the normal dominant allele F. Consider a couple who both have the genotype Ff. Their first child did not get cystic fibrosis. What is the chance that their second child will develop cystic fibrosis?
Biology · High School · Wed Jan 13 2021
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If both parents have the genotype Ff and their first child did not get cystic fibrosis, it indicates that the first child inherited the dominant allele F from one parent and the recessive allele f from the other. The probability of each parent passing on the recessive allele f is 50%.
For the second child, the alleles are segregated independently during gamete formation. Therefore, the probability of the second child inheriting the recessive allele f from both parents (resulting in cystic fibrosis) is 25% (0.5 * 0.5). The chance of the second child not developing cystic fibrosis is 75%.