question archive Congenital hearing loss can be due to the inheritance of recessive mutations

Congenital hearing loss can be due to the inheritance of recessive mutations

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Congenital hearing loss can be due to the inheritance of recessive

mutations. Two deaf people marry and have three children.


(a) Assuming that the parents' hearing loss has a genetic basis, what proportion of the children would you expect to be deaf?
(b) All three children in fact have normal hearing. What do you deduce from this observation about the relationship of the mutant genes in the parents?
(c) Use the standard genetic format to write down the likely genotypes of the parents and children. Use the symbols A and a to denote normal and mutant alleles, and 1, 2, etc. to define different genes or loci. Thus A1, a1 and A2, a2 define two alleles of each of two different genes.
(d) One of the daughters of the deaf parents above now wishes to have children. Using chromosome diagrams, draw all the possible gametes which she would produce.
(e) What is the probability that the daughter's children would be deaf if
(i) she had children with a man with normal hearing?
(ii) she had children with a man who was deaf (with genotype e.g. a1/a1 A2/A2)


If you could explain to me how to work out each of these questions it would be appreciated as I am struggling with my genetics module. Reference Uni question from 'Molecules, Genes and Disease 2007/2008'

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