In humans Tay Sachs disease is a recessive trait in humans t

In humans, Tay Sachs disease is a recessive trait in humans that causes abnormal accumulation of lipid in the brain because of alteration in lipid metabolism. Persons al looted with this disease usually die by age 4. If two normal heterozygous intend on having four children. what is the probability that three will be normal and one child will have the full blown Tay Sachs disease? what is the probability that the first three children will have Tay Sachs and the fourth will be normal?

Solution

Tay Sachs disease is an autosomal recessive genetic disorder which causes progressive deteriorartion of the nerve cells and hence the development of the child.. The children affected with the disease lose motor skills and mental functions and become deaf,blind and mentally retarded. They do not survive beyond the age of 5.The disease is recognized usually by a dark red spot on the retina.

The disease results due to a mutation of the HEXA gene on chromosome number 15. This gene is responsible for the production of the enzyme hexaaminidase A. the enzyme brings about the degradation of unwanted fats that accumulate in the brain. In absence of the enzyme the fats get accumulated and cause progressive damage to the nervous system .

Since it is an autosomal recessive disorder and since both the parents are heterozygous carriers the chance of off spring developing the disease is 50% and hence the chance of the first child developing the disease is 100%.

b. since both the parents are carries only one of the child will be normal the other two hetrozygous carrier and one will be affected but not all the three.