Cystic fibrosis (CF) is an autosomal recessive disorder in...

Cystic fibrosis (CF) is an autosomal recessive disorder in humans. If two unaffected individuals have a child with $\mathrm{CF}$, what is the chance that their second child will have CF?
a. $25 \%$
b. $50 \%$
c. $75 \%$
d. $100 \%$
e. None of these are correct.

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Key Concepts

Autosomal Recessive Inheritance

This concept describes a mode of inheritance in which two copies of an abnormal gene must be present in order for a trait or disorder to develop. Individuals who are heterozygous for the gene (carriers) do not exhibit symptoms of the disorder, but they can pass the recessive allele to their offspring. When both parents are carriers, each child has a 25% chance of inheriting two copies of the recessive allele and thus expressing the disorder.

Carrier

A carrier is an individual who harbors one copy of a recessive allele for a genetic disorder but does not show any symptoms of the condition. Carriers play a crucial role in autosomal recessive inheritance because when two carriers have a child, there is a possibility that the child inherits the recessive allele from each parent, leading to the manifestation of the disorder.

Punnett Square

The Punnett square is a graphical tool used in genetics to predict the probability of offspring inheriting particular alleles from their parents. By laying out the possible combinations of parental alleles, it helps to visualize and calculate the likelihood of genotypes and corresponding phenotypes in the offspring, such as the 25% chance for a child to have an autosomal recessive disorder when both parents are carriers.

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