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.
What conclusions could be drawn if their first child had been deaf?
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Essentials of Genetics Plus Mastering Genetics with eText -- Access Card Package (9th Edition) (Klug et al. Genetics Series)
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The couple knew that this condition is inherited as an autosomal dominant trait, but they were unsure what kind of physical manifestations a child would have if it inherited both mutant alleles. They were each heterozygous for the FGFR3 (MIM 134934) allele that causes achondroplasia. Normally, the protein encoded by this gene interacts with growth factors outside the cell and receives signals that control growth and development. In achrodroplasia, a mutation alters the activity of the receptor, resulting in a characteristic form of dwarfism. Because both the normal and mutant forms of the FGFR3 protein act before birth, no treatment for achrondroplasia is available. The parents each carry one normal allele and one mutant allele of FGRF3, and they wanted information on their chances of having a homozygous child. The counsellor briefly reviewed the phenotypic features of individuals with achondroplasia. 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