What type of genetic disease has a one-in-four chance of being inherited by a second child?

What type of genetic disease has a one-in-four chance of being inherited by a second child?

• A. Autosomal dominant disease
• B. Autosomal recessive disease
• C. X-linked disease
• D. Mitochondrial disease

Answer: (B)

Autosomal recessive diseases are characterized by the requirement of two copies of the mutated gene for the disease to manifest. If both parents are carriers of a recessive gene, each child they have has a one in four chance of inheriting the disorder. This arises because there are three potential combinations from the alleles: one for the affected allele from each parent (which results in the disease), one for one affected and one normal (a carrier, but unaffected), and one for two normal alleles (neither affected nor a carrier).

In the context of family genetics, if parents are both carriers (heterozygous for the same recessive gene), the probability for a child to inherit the genetic disease is indeed one in four. This pattern of inheritance explains why, after one affected child, the odds of having another child with the same autosomal recessive disorder remains at approximately 25%.

Conversely, autosomal dominant diseases typically present a 50% probability of inheritance if one parent has the disease, while X-linked diseases usually affect males more severely and alter probabilities based on the sex of the offspring. Mitochondrial diseases follow a different inheritance pattern, as they are passed from mothers to all offspring but not from fathers.