Tay-Sachs disease is caused by a mutation of one nucleotide for a protein that disrupts the activity of an enzyme in the brain. This leads to a toxic level of a substance to build up in neurons in the brain and spinal cord, leading to severe brain damage and eventually death. Why do you think that the change in one nucleotide can cause Tay-Sachs disease to be fatal, whereas the change in one nucleotide causes sickle cell disease, a disease in which a person can lead a functional life?

Explanation:

Tay Sachs disease is a genetic disorder caused by the mutation in the gene which codes for the enzyme that breaks down the ganglioside in the brain and the spinal cord. The Tay Sachs disease proves fatal to lives as the mutation is involved in the enzyme involved in the metabolism in the brain and spinal cord.

The Sickle cell anaemia is a disease which is caused by the mutation in the gene which causes the change in the cellular structure. The shape of the red blood cells does not prove fatal not all the red blood cells are affected with this and some cells can transport the oxygen.

i'm pretty sure questions like these aren't allowd.   but, sure.   i can and talk : ))