Autosomal recessive

Autosomal recessive is a pattern of inheritance involving a recessive allele that is carried on an autosome. Autosomal recessive diseases include cystic fibrosis. As with all cases of autosomal inheritance, sex is irrelevant in the transmission of the disease (i.e. males and females are equally likely to be inherited). If a person is heterozygous for an autosomal recessive disease then they are said to be carriers of the disease; when two carriers mate, 25% of the offspring are expected to have the disease.

Below is an example of a pedigree that shows an autosomal-recessive pattern of inheritance:

Pedigree 4
Pedigree 4

Some of the hallmarks of an autosomal recessive pattern of inheritance are:

  • Sex of the parent and of the child is irrelevant in the transmission of the disease

  • Affected individuals are almost always born to unaffected (carrier) parents. This is because the probability of two parents who have the disease mating, given that the frequency of recessive diseases in the general population is 1 in 10,000, is about 1 in 100,000,000. Using the same statistic, the likelihood of a heterozygote carrier mating with an affected person is 1 in 250,000. Finally, the chance of two heterozygote carriers mating is 1 in 2500; by far the most likely scenario.

  • For every child they have, two carrier parents have a 1 in 4 chance of having an affected child. Because the child would have to inherit one recessive allele from each parent, and according to Mendelian segregation ratios there is a 25% chance of this occurring.

  • Recessive diseases are more likely in the children of related (consanguineous) parents, since related parents are more likely than the general population to both carry a recessive allele

  • For an affected individual, the trait is more likely to be seen in their siblings than in either their parents or their offspring