Question

Esther and Sam go for genetic testing before having children. They both find out that they are both carriers for the autosomal recessive diseases Tay-Sachs disease and for PKU (Phenylketonuria).

a. What are the genotypes of Sam and Esther? (5 points)

b. What are their possible gametes? (5 points)

c. Draw a Dihybrid cross (10 points) on a separate sheet of paper and answer the following questions. i. What is the probability of having a child unaffected by either disease? (5 points) ii. What is the probability of having a child having PKU but not Tay-Sachs? (5 points) iii. What is the probability of having a child having Tay – Sachs but not PKU? (5 points) iv. What is the probability of having a child with both diseases? (5 points)

please describe with Punett squate

Answer 1

let P be the normal allele and p for PKU, T normal allele, and t for Tay-Sachs diseases.

A- SO, the genotype of Sam and Esther is PpTt.

B- possible gametes - PT, Pt, pT, and pt.

Tay-Sachs disease and for PKU is the autosomal recessive diseases, Person will only show the diseases if both the recessive alleles are present in its genome.

i. What is the probability of having a child unaffected by either disease - There are nine genotypes out of 16 which have at least one normal allele. So the probability is 9/16.

ii. What is the probability of having a child having PKU but not Tay-Sachs - There are three children who have pp genotypes. So the probability is 3/16.

iii. What is the probability of having a child having Tay – Sachs but not PKU - There are three children who have tt genotypes. So the probability is 3/16.

iv. What is the probability of having a child with both diseases - There is only one child whose genotype is pptt. So the probability is 1/16

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