Autosomal recessive disorders are expressed in what percentage of offspring from two heterozygous parents?

When two heterozygous parents (each carrying one dominant and one recessive allele) have offspring, the inheritance pattern of an autosomal recessive disorder follows a classic Mendelian ratio. Each parent contributes one allele to their offspring.

For two heterozygous parents, the possible combinations of alleles in their offspring can be represented as follows:

• AA (homozygous dominant)

• Aa (heterozygous)

• Aa (heterozygous)

• aa (homozygous recessive)

This results in a genotypic ratio of 1 AA : 2 Aa : 1 aa. Out of these combinations, it is the aa genotype that represents the autosomal recessive disorder. Therefore, the proportion of offspring that will express the autosomal recessive condition is 1 out of 4, or 25%.

This means that in a scenario involving two heterozygous carriers, the expected percentage of offspring expressing the disorder due to inheriting the recessive alleles from both parents is indeed 25%.