Concept explainers
CASE STUDY | But he isn't deaf
Researching their family histories, a deaf couple learns that each of them has relatives through several generations who are deaf. With a rudimentary understanding of genetics, they also learn that one of many forms of deafness can be inherited as an autosomal recessive trait. They plan to have children, and based on the above information, they are concerned that some or all of their children may be deaf. To their delight, their first child has normalhearing. The couple turns to you as a geneticist to help explain this situation.
Is it likely that these parents inherited their deafness as an autosomal recessive trait?
To analyze:
The query of a deaf couple having a normal first child that whether the deafness in the couple is due to autosomal recessive inheritance.
Introduction:
In the given case, a deaf couple learn that they had relatives who were deaf. Despite the fact and expecting some of their children to be deaf, they bear a normal firstborn baby. Deafness, also known as hearing impairment, can be caused by genetic inheritance of trait from one generation to another. Inherited deafness is present in 50% (percent) of the deaf population.
Explanation of Solution
It can be inherited in the form of autosomal recessive trait or autosomal dominant trait. In autosomal recessive deafness, both the alleles for deafness must be present in order to cause deafness; whereas in autosomal dominant deafness, single allele is able to cause deafness in the offspring.
Parents do not have both the alleles for deafness, because the first child born is normal. In case, both had a pair of recessive allele for deafness, the first child would be deaf as well. Therefore, the deafness inherited in this case is not due to autosomal recessive inheritance.
If it was a case of recessive inheritance, then
DD X DD= DD; DD; DD; DD, all the children would be deaf. But, this is not true.
D: deaf, d: normal
Therefore, it can be concluded that this is not the case of autosomal recessive inheritance. Parents might have inherited deafness, but not through autosomal inheritance.
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Chapter 4 Solutions
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