Recessive - Autosomal Recessive Gene

Autosomal Recessive Gene

Autosomal recessive or autorecessive is a mode of inheritance of genetic traits located on the autosomes (the 22 non-sex determining chromosomes).

In opposition to autosomal dominant trait, a recessive trait only becomes phenotypically apparent when two copies of a gene (two alleles) are present. In other words, the subject is homozygous for the trait. Recessive genes will also show a horizontal inheritance on a pedigree chart. The frequency of the carrier state can be calculated by the Hardy-Weinberg formula: (p is the frequency of one allele, and q = 1 − p is the frequency of the other allele. Thus p*p is the frequency of the homozygous genotype for the first allele, 2pq is the frequency of the heterozygous genotype, and qq is the frequency of the other homozygous genotype.)

Recessive genetic disorders occur when both parents are carriers and each contributes an allele to the embryo. As both parents are heterozygous for the disorder, the chance of two disease alleles being inherited by one of their offspring is 25% (in autosomal dominant traits this is higher). 50% of the children (or 2/3 of the remaining ones) are carriers. When one of the parents is homozygous, the trait will only show in his/her offspring if the other parent is also a carrier. In that case, the chance of disease in the offspring is 50%.