An autosomal recessive disease occurs when an individual is __________.
A) heterozygous for a dominant, disease-causing allele
B) codominant for a recessive, disease-causing allele
C) homozygous for a dominant, disease-causing allele
D) homozygous for a recessive, disease-causing allele

Question

Quizplus · Accepted Answer

An autosomal recessive disease occurs when an individual has two copies of the recessive, disease-causing allele (homozygous recessive genotype). In this case, the individual does not have a functional copy of the gene, as the recessive allele "masks" the effects of the dominant allele. Heterozygotes (Aa) are carriers of the disease-causing allele, but do not necessarily show symptoms of the disease, as their functional copy of the gene is still able to produce enough of the necessary protein(s). Codominance describes a situation where both alleles are equally expressed in the phenotype, which is not relevant to autosomal recessive diseases. Homozygosity for a dominant, disease-causing allele would result in expression of the dominant phenotype, regardless of the presence of a functional allele on the other chromosome.

An Autosomal Recessive Disease Occurs When an Individual Is __________