Why do you think that the change in one nucleotide can cause tay-sachs disease to be fatal

The protein is completely disrupted and it can not perform its function

Explanation:

Tay-Sachs disease is a rare degenerative disease and autosomic recessive. It affects the brain and central nervous system. It occurs when the body lacks hexosaminidase A, which is a protein that helps break down a group of chemicals found in nerve tissue, called gangliosides. Without this protein, gangliosides build up in cells, often in neurons in the brain.

Tay Sachs disease is caused by a mutation of one nucleotide for a protein that disrupts the activity of an enzyme in the brain. Proteins are synthesized according to the DNA sequence. Every three bases (called a codon), one of the many amino acids that will form the protein is synthesized. When one of these bases is mutated, it is very possible that a different amino acid is synthesized instead. Sometimes that doesn't happen because the genetic code is degenerated and different codons can give rise to the same amino acid. But in this mutation, the protein is completely disrupted and it can not perform its function. Then, the brain is affected as it was explained and results fatal.

the major parts of the digestive system:

salivary glands.

pharynx.

esophagus.

stomach.

small intestine.

large intestine.

rectum.

accessory digestive organs: liver, gallbladder, pancreas.

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.