The incidence of Tay Sachs, an autosomal recessive disorder, is approximately 1 in 3,500 in a certain population. Assuming Hardy-Weinberg equilibrium, what is the probability that Sarah, who is phenotypically normal with no family history, and Tom, who despite having an affected sister is phenotypically normal like his parents, will have a child with Tay Sachs

If Tom is either normal in genotype or an heterozygote, and mates with Sarah: with no history, there is zero percent chance of producing a child with Tay Sachs.

Explanation:

The incidence of Tay Sachs, an autosomal recessive disorder. For the trait to  be expressed, two copies has to be inherited from both parent meaning both parents has to be carriers of the trait.

Thus, Tom, who has a sis that is affected can either be a genotypically normal individual or an heterozygote like his parent.

If Tom is either normal in genotype or an heterozygote, and mates with Sarah: with no history, there is zero percent chance of producing a child with Tay Sachs.

Tom        T    T      or        T      t

Sarah

  T        TT   TT               TT    Tt

  T        TT   TT               TT    Tt

AU

Explanation:

AU is also know as the astronomical units which is the closest to the distance of the earth to the sun.