For each of the following 1) indicate the genotypes of the parents, 2) provide a

Question

For each of the following 1) indicate the genotypes of the parents, 2) provide a Punnett Square depicting the particular example and list 3) phenotypic and 4) genotypic ratios of the possible outcomes.

Phenylketoneuria is an autosomal recessive disorder in which individuals cannot tolerate much of the amino acid phenylalanine. It can cause poor cognitive development and a host of other problems. A couple, each of which is a heterozygote for the condition, have a child. Provide the information requested in the introduction for this cross.

Explanation / Answer

Parents are unaffected carriers

Genotype of parents = Rr

Punnet square

              R               r

R          RR            Rr

r           Rr              rr

RR = Unaffected and non-carrier

Rr = Heterozygous unaffected but carrier

rr = Affected

Phenotypic ratio = 3 : 1   ( 3 unaffected and 1 affected)

Genotypic ratio = 1 : 2 : 1

where 1 = unaffected non-carrier , 2 unaffected carrier and 1 affected individual

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