Unlike an autosomal dominant trait, the characteristics of a recessive trait can only be expressed if both alleles are recessive. If a recessive allele is paired with a dominant allele, then the dominant allele will cancel out the expression ofÂ recessive allele.
The first characteristic of an autosomal recessive trait is that males and females are equally likely to inherit an autosomal recessive trait from their parents. Like autosomal dominant traits, autosomal recessive traits are not sex-linked traits,Â makingÂ it equally likely for males and females to inherit an autosomal recessive trait.
The second characteristic of autosomal recessive traits is that the disease is usually found in siblings. Parents of affected siblings are usually unaffected. For example, my dragon inherited the recessive trait for a chin spike. It’s genotype was aa whereas it’s parents’ genotypes were both Aa. Since both parents have a dominant allele present, they do not portray the recessive characteristic. If my dragon had siblings, they would also have the chance of having the recessive trait being expressed.
The third characteristic of autosomal recessive traits is that all offspring of an affected parent are carriers. For example, the father of my dragon had the genotype KK whereas it’s mother had the genotype kk. The father had dominant, orange eyes and the mother had recessive, yellow eyes. When my dragon was born it automatically was a carrier of the recessive trait because both of it’s mother’s alleles were recessive.Â
The fourth characteristic of autosomal recessive traits is that if a child is born to two carrier parents and is not affected, then there is a 2/3 that it is a carrier. For example, my dragon’s parents were both heterozygous for the trait that expresses whether a dragon has Â spots on it’s thigh or not. They both had no spots on their thighs and so did my dragon when it was born, but it was still a carrier like it’s parents.Â
The fifth and final characteristic of autosomal recessive traits is that two carrier parents have a 25% chance of having an affected child and a 75% chance of having an unaffected child. This is because the likelihood of having two recessive alleles paired together when both the parents are heterozygous is low. Â In the example above, my dragon was unaffected and fell under the most probable scenario.
Genetics primer – what is autosomal recessive inheritance? (n.d.). Retrieved June 17, 2015, from NCHPEG website: http://www.nchpeg.org/dentistry/index.php?option=com_content&view=article&id=22&Itemid=55&limitstart=5