Question

A breeder is considering purchasing an Arabian stallion and is concerned he might be a carrier of severe combined immunodeficiency syndrome (SCID), an autoimmune disease that causes early death among homozygous recessive foals. The frequency of the SCID allele is estimated to be 7% in the general Arabian horse population.

a. If the stallion had produced no affected offspring from 100 matings to randomly selected mares, what would be the breeder’s confidence that he does not carry the SCID allele?

b. How many matings to randomly selected mares (with resulting unaffected offspring) would it take to be 99% confident that the stallion does not carry the SCID allele?

Answer 1

Answer a-

If there were no affected individual, then the breeder would have 100% confidence. It is because we have no negative case.

Answer b

In one cross, we have 7 % or 0.07 chances to have SCID, now after each cross there will be decrease of chances of having disease.

Consider this formula for having total numbers of generations to get required percentage-

N x r ?R

Here N is the numbers of generations. The r is the prescribed percentage chances of having the disease. The R indicates the required chances of having no disease or confidence.

N x 0.07 ?0.99

N ?0.99 / 0.07

N?14.14

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