Autosomal Recessive Traits and Disorders

1. Autosomal Recessive

Autosomal recessive traits and disorders are caused by the inheritance of recessive traits on autosomes. Autosomes are all the chromosomes in your body, excluding the sex chromosomes.

In order for a person to inherit an autosomal recessive trait or disorder, both parents must contribute recessive alleles. A person with an autosomal recessive trait or disorder has a genotype with two recessive alleles. They would be homozygous recessive.

What are the odds certain parents would end up with offspring that are homozygous recessive? Punnett squares can be used to help find out the chances:

The first square shows the odds two people who are both heterozygous (carriers) for a particular trait of having an offspring that is homozygous recessive. A capital letter indicates that the trait is dominant, and the lower case letter shows the recessive trait.

The second square shows a parent that is heterozygous (a carrier) for a trait with someone who is homozygous recessive (someone whose phenotype shows the recessive trait).

The third square shows two people that are homozygous recessive.

There really is no need to make a square for two people that are both homozygous dominant because they will always produce children with the dominant gene.

It is important to note that someone who is heterozygous for a trait is a carrier for the recessive trait. They won't display the characteristics of it because they display the dominant trait, but they can still pass the recessive allele on to their offspring.

term to know

Autosomal Recessive

A trait or disorder caused by the inheritance of two recessive alleles on an autosome.

2. Autosomal Recessive Disorders

Cystic fibrosis is a type of autosomal recessive disorder in which mucus will build up in the lungs along with other different symptoms.

Phenylketonuria (PKU) is another autosomal recessive disorder in which the buildup of a certain amino acid will get too high in a person's body. If they get too much of this certain amino acid built up in their body, it can cause mental retardation. Diet can help lower the specific amino acid and help prevent symptoms of this disorder.

terms to know

Cystic Fibrosis

An autosomal recessive disorder that results in buildup of mucus in the lungs.

Phenylketonuria (PKU)

An autosomal recessive disorder that results in the buildup of phenylalanine (an amino acid) in the body that can lead to mental retardation if levels exceed a certain point.