Autosomal recessive

Genetics - autosomal recessive; Inheritance - autosomal recessive

Autosomal recessive is one of several ways that a trait, disorder, or disease can be passed down through families.

An autosomal recessive disorder means two copies of an abnormal gene must be present in order for the disease or trait to develop.

Inheriting a specific disease, condition, or trait depends on the type of chromosome that is affected. The two types are autosomal chromosomes and sex chromosomes. It also depends on whether the trait is dominant or recessive.

A mutation in a gene on one of the first 22 nonsex chromosomes can lead to an autosomal disorder.

Genes come in pairs. One gene in each pair comes from the mother, and the other gene comes from the father. Recessive inheritance means both genes in a pair must be abnormal to cause disease. People with only one defective gene in the pair are called carriers. These people are most often not affected with the condition. However, they can pass the abnormal gene to their children.

CHANCES OF INHERITING A TRAIT

If you are born to parents who carry the same autosomal recessive change (mutation), you have a 1 in 4 chance of inheriting the abnormal gene from both parents and developing the disease. You have a 50% (1 in 2) chance of inheriting one abnormal gene. This would make you a carrier.

In other words, for a child born to a couple who both carry the gene (but do not have signs of disease), the expected outcome for each pregnancy is:

  • A 25% chance that the child is born with two normal genes (normal)
  • A 50% chance that the child is born with one normal and one abnormal gene (carrier, without disease)
  • A 25% chance that the child is born with two abnormal genes (at risk for the disease)

Note: These outcomes do not mean that the children will definitely be carriers or be severely affected.

X-linked recessive genetic defects

There are several X-linked (or sex-linked) recessive genetic disorders, (hemophilia, muscular dystrophy) which are inherited through a genetic defect on an X chromosome. A female has 2 X chromosomes, one she inherited from her mother and one she got from her father. A male has an X chromosome from his mother and a Y chromosome from his father. If a woman has the defect on one of her X chromosomes, and the father's X chromosome is normal, there is a 25% chance for each pregnancy to produce an unaffected girl; a girl who carries the defect; an unaffected boy; or a boy with the disorder.

Genetics

Genetics is the study of heredity and how traits are passed along from parents to offspring. Genes are contained within the chromosomes found within the egg and sperm. Each parent contributes one half of each pair or 23 chromosomes to their child, 22 autosomal and 1 sex chromosome. The inheritance of genetic diseases, abnormalities, or traits is described by both the type of chromosome the abnormal gene resides on (autosomal or sex chromosome), and by whether the gene itself is dominant or recessive.

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