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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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