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Autosomal Recessive Traits

Autosomal Recessive Traits

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This lesson will identify how inherited recessive alleles on autosomes can cause various genetic disorders.

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Tutorial

What's Covered

This lesson is going look at autosomal recessive traits and disorders by examining:

  1. Autosomal Recessive
  2. Autosomal Recessive 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.

Term to Know

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

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:recessive.png

The first square shows the odds two people who are both heterozygous 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. They are considered carriers. Both of them are considered carriers because they possess this recessive allele.


The second square shows a parent that is heterozygous for a trait with someone who is homozygous recessive. The last square shows two people that are homozygous recessive. There is no need to make a square for someone who is 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 dominate trait, but they can still pass it on to their offspring. 


2. Autosomal Recessive Disorders

Cystic fibrosis and PKU are examples of autosomal recessive traits.

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

Phenylketonuria, or 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.

Term 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.

Summary

Autosomal Recessive traits and disorders are caused by inheritance of recessive traits on the autosomes. These are all the chromosomes in your body besides your sex cells. In order for this to express in a person, they must inherit recessive genes from both their parents. Some autosomal recessive disorders include cystic fibrosis and phenylketonuria.

Keep up the learning and have a great day!

Source: This work is adapted from Sophia Author Amanda Soderlind

TERMS TO KNOW
  • Phenylketonuria (PKU)

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

  • Cystic Fibrosis

    An autosomal recessive disorder that results in build-up of mucus in the lungs.

  • Autosomal Recessive

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