In dogs, mutations in a single autosomal gene can produce deadness. Dogs who are

Question

In dogs, mutations in a single autosomal gene can produce deadness. Dogs who are DD or Dd can hear, but those who are dd are deaf. Rex, who can hear, is mated with Rinny, who can also hear. in their first litter of pups, two are deaf and the other three can hear.

In dogs, as in humans, sex is determined by X and Y chromosomes. (XX=female, XY=male). What is the probablility that in a second litter of pups, the first will be a deaf female?

What is the possibility that a male pup from Rex and Rinny will be able to hear, but will be CARRIER for the deafness allele?

I worked these out and I'm not getting the right answer each time. Please help.

Explanation / Answer

It is given that Rex and Rinny bothncan hear but some of their their children are deaf and the condition is autosomal recessive . therefore only those offsprings havinf homozygous recessive condition will be affected ones.

therefore both must be carrier of the condition of mutation .

therefore the cross will be between Aa X Aa

thecross will lead to AA, Aa, Aa, aa

therefore 25 % will be affected.or the probability of being affected is 1/4.

on the other hand XX x XY

resulting into, XX, XX, XY, XY

there is 1/2 probability of being a girl or being a boy.

Probability of first female being affected will be (multiplication rule of probability)

= 1/4 X 1/2

=1/8.

b. probability of carriers = 2/4= 1/2

and being male probability = 1/2

therefore affected and male probability are = 1/2 X 1/2

= 1/4.

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