Respuesta :
Phenylketonuria is an inherited disease caused by a recessive autosomal allele. If a woman and her husband are both carriers, the probability that their first child will be a phenotypically normal girl is (D) 3/8.
The dominant normal allele can be denoted by the letter P and the recessive allele for phenylketonuria can be denoted by the letter p. As it is given that both the parents are carriers of the disease, therefore, they must both possess the genotype Pp.
From the Punnett square it can be observed that there is a probability of 3/4 that the child will be born with a normal phenotype. Both the PP and Pp genotypes will result in a normal phenotype as the normal P allele is dominant.
Apart from this, there is also a probability of 1/2 of the first child being born as a girl.
Thus, multiplying 3/4 and 1/2 together we get 3/8 as the result.
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