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Autosomal recessive inheritance |
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Everybody has two copies of each of their genes, which are inherited from their parents.
One copy is inherited from the father and the other from the mother (there are about 60,000 different
genes, and two copies of each).
When a person is a "carrier" of an inherited disease, he has one normal gene and one abnormal gene
for the condition. In autosomal recessive inheritance, the action of the healthy gene predominates over
that of the abnormal gene.
This means that a person who carries one abnormal gene (a carrier) is healthy and does not show any
clinical signs of the disease.
However, when two people who are both carriers of the same abnormal gene marry, there is a 25% risk in
each pregnancy that each parent will transmit the abnormal gene to the child.
This child will then have 2 abnormal genes and no normal ones for the disease in question and will
therefore suffer from the disease.
In this inheritance pattern both males and females are affected equally and with the same degree of
severity.
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Examples of diseases transmitted by autosomal recessive inheritance include Tay Sachs disease
and cystic fibrosis.
Current research is concerned with developing tests to identify carriers of genes for severe diseases
and also tests that can be used for prenatal diagnosis in cases where both parents are carriers.
Tests for identifying carriers will develop rapidly once the genes for the various diseases have
been identified.
In the near future kits for these tests should become available.
A number of such kits are already available, including for Tay Sachs disease, cystic fibrosis, etc.
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