Question

A woman is planning to marry her first cousin, but the couple discovers that their shared grandfather’s sister died in infancy of Tay-Sachs disease (a rare autosomal recessive disorder).

a) Draw the relevant parts of the pedigree as described, and show all the genotypes as completely as possible.

b) What is the probability that the cousins’ first child will have Tay-Sachs disease, assuming that all people who marry into the family are homozygous normal?

Answer 1

Q) The woman is planning to marry her first cousin , but they discovers that their shared grandfather's sister died in infancy due to Tay-Sach's disease (a rare autosomal recessive disorder).

Draw the relevant parts of the pedigree as described, and show all genotypes.

Answer:- Tay-sach's disease is an autosomal recessive disorder, in autosomal recessive disorder traits appear equally in males and females, if parents are healthy carriers than 25% of children gets affected.

in the above chart as per question The woman who is planning to marry her first cousin, discovers that their shared grandfather's sister is affected by Tay-sach's disease, so in

Generation-1 , Grand fathers parents were both carriers of the disease (Tt * Tt)

Generation-2 they gave rise to four children 1 normal female, 1 carrier male, 1 affected female and 1 carrier male.

In Generation-2, carrier male (Women's shared grandfather )married to a normal female (Tt * TT)

In Generation-3 they had 4 children 1 is normal male, 1 carrier female, 1 normal male , 1 carrier female.

In Generation-3 carrier female got married to a normal male (Tt * TT)

In Generation-4 they gave rise to 1 normal female , 1 carrier male, 1 normal female, 1 carrier male.

and in Generation-3, the mating between a normal male and normal female (TT * TT) gave rise to Normal childs.

In Generation -4 when IV- 3 married with IV - 4 , here both are normal male and female .(TT * TT)

So in Genartion -5 all the child's will be normal ,

so the chance of cousin's first child having Tay-sach's disease is 0% , it will be a normal child.

as all the people who marry into the family are homozygous normal.