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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
Eduncle
Dear Student,
When a genetic disorder is diagnosed in a family, family members often want to know the likelihood that they or their children will develop the condition. This can be difficult to predict in some cases because many factors influence a person'schances of developing a genetic condition. One important factor is how the condition is inherited. For example:
It is important to note that the chance of passing on a genetic condition applies equally to each pregnancy. For example, if a couple has a child with an autosomal recessive disorder, the chance of having another child with the disorder is still 25 percent (or 1 in 4). Having one child with a disorder does not “protect” future children from inheriting the condition. Conversely, having a child without the condition does not mean that future children will definitely be affected.
DMD is inherited in an X-linked pattern because the gene that can carry a DMD-causing mutation is on the X chromosome. Every boy inherits an X chromosome from his mother and a Y chromosome from his father, which is what makes him male. Girls get two X chromosomes, one from each parent.
Each son born to a woman with a dystrophin mutation on one of her two X chromosomes has a 50 percent chance of inheriting the flawed gene and having DMD. Each of her daughters has a 50 percent chance of inheriting the mutation and being a carrier. Carriers may not have any disease symptoms but can have a child with the mutation or the disease. DMD carriers are at risk for cardiomyopathy.
Although DMD often runs in a family, it is possible for a family with no history of DMD to suddenly have a son with the disease. There are two possible explanations. The first is that the genetic mutation leading to DMD may have existed in the females of a family for some generations without anyone knowing. Perhaps no male children were born with the disease, or, even if a boy in an earlier generation was affected, relatives may not have known what disease he had.
The second possibility is that a child with DMD has a new genetic mutation that arose in one of his mother’s egg cells. Because this mutation is not in the mother’s blood cells, it is impossible to detect by standard carrier testing.
A man with DMD cannot pass the flawed gene to his sons because he gives a son a Y chromosome, not an X. But he will certainly pass it to his daughters, because each daughter inherits her father’s only X chromosome. They will then be carriers, and each of their sons will have a 50 percent chance of developing the disease and so on.
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