Any of a large number of different recessive mutations cause profound hereditary

Question

Any of a large number of different recessive mutations cause profound hereditary deafness. Children homozygous for such mutations are often found in small, isolated communities in which matings tend to be within the group. In these instances, a mutation that orginates in one person can be transmitted to several members of the population in future generations and become homozygous through a marriage between group members who are carriers. A deaf man from one community marries a deaf woman from a different, unrelated community. Both of them have deaf parents. The marriage produces three children, all with normal hearing. How can you explain this result?

Explanation / Answer

It depends on two things. First, whether the parents carry any of the specific gene for deafness. Second, the type of gene the parents carry. There are few dominant genes associated with deafness. One example for this is waanderburg syndrome. In this kind of syndrome even if one parent carries the dominant gene it results in deaf offspring. Another case is when the parents carry the recessive gene. It results in usher's syndrome or connexin 26 gene. In these cases both the parents should carry the same gene.

Only about 10% of deaf parents have deaf offspring. 40-50% chances of being parents deaf is due to environmental factor such as ototoxic drug, prematurity, trauma, CMV ( cytomegalovirus infection) . Because this cause is not genetical therefore the children's are not deaf.

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