Genetic Condition, Pregnancy, Birth defects and Genetics
Every child receive chromosomes from your mother and father and with them the
genes that make up your genetic code. A genetic condition is due to a mistake
or mutation in the genetic code on a chromosome. In addition, the gene can be
passed from parent to child. An example of a genetic condition is sickle-cell
anaemia, in which there is an abnormality in the gene controlling the formation
of the red blood cells that carry oxygen around the body.
Thalassaemia is another genetic condition in which there is an abnormality in
the gene controlling the production of red blood cells, leading to varying
degrees of anaemia. Another example of a genetic condition is cystic fibrosis, in
which the mucus produced by the lungs is abnormally thick and difficult to
clear, leading to recurrent chest infections. In this condition there is also
abnormality of the pancreas, affecting its ability to produce enzymes to break
down food in the gut and thus leading to malabsorption of food.
Some genetic conditions are dominant , others are recessive. Sickle-cell
anaemia, like cystic fibrosis, is a so-called ' recessive ' condition because for a
baby to be affected it needs to inherit two sickle-cell genes , one from each parent.
Each parent will pass the gene to the child at conception. If one parent
pa s se s on the sickle-cell gene and the other passes on a normal gene, this is
not sufficient to cause the condition. To pass on the two sickle-cell genes
necessary to produce the disease each parent will have to be either affected by
the disease or be a carrier of it. A carrier has one normal gene and one
abnormal gene. Carriers do not usually have the disease, but have the potential
to pass this gene on to a child. They are unlikely to know that they have the
gene unless there is a family history of the disease.
Occasionally the abnormal gene can be dominant , however, as in the case
of brittle bone disease and Huntingtons chorea in which brain cells degenerate,
leading to jerky, involuntary movements and progressive dementia. This means
that if the baby has one abnormal gene it will be affected even if the other gene
is normal. In dominant conditions only one parent need carry and pass on the
gene.
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