Question

huntingtons disease is a hereditary neurological disorder that causes progressive loss of muscle control, changes in thinking, and emotional difficulties, often beginning in mid-adulthood. it is caused by a mutation in the htt gene, where a dna segment made of the letters cag is added many more times than normal. this expanded repeat leads to the production of a toxic form of the huntingtin protein, which gradually damages nerve cells in the brain. what kind of mutation causes huntingtons disease? hint: is it a substitution, insertion, or deletion

Explanation:

The problem states that in Huntington's disease, a DNA segment (CAG) is added many more times than normal. In genetics, when extra nucleotides (here, the CAG segment) are inserted into the DNA sequence, it is called an insertion mutation. A substitution mutation would involve replacing one nucleotide (or segment) with another, and a deletion mutation would involve removing nucleotides. Since the description is about adding (inserting) the CAG segment multiple times, it is an insertion mutation.

Answer:

Insertion mutation.