The genetic defect responsible for \(\mathrm{HD}\) is a. A small sequence of DNA on chromosome 4 in which several base pairs are repeated many, many times. b. The normal gene has three DNA bases, composed of the sequence CAG. c. In people with \(\mathrm{HD}\), the sequence abnormally repeats itself dozens of times. d. Over time-and with each successive generations-the number of CAG diminishes. e. All and above f. a, b, and c only

Let's examine each statement carefully to determine if it is true or false. a. A small sequence of DNA on chromosome 4 in which several base pairs are repeated many, many times. - This statement is true. HD is caused by a repeating DNA sequence on chromosome 4. b. The normal gene has three DNA bases, composed of the sequence CAG. - This statement is true. The sequence CAG constitutes a triplet that encodes for an amino acid (glutamine) in the normal gene. c. In people with HD, the sequence abnormally repeats itself dozens of times. - This statement is true. The CAG triplet repeats itself much more frequently in people with HD than in unaffected individuals. d. Over time-and with each successive generations-the number of CAG diminishes. - This statement is false. In HD, the number of CAG repeats generally increases as the disease is passed down from generation to generation. e. All and above - Since not all the statements are true, this option is incorrect. f. a, b, and c only - Since statements a, b, and c are the only true statements listed, this option is correct.

We have determined that statements a, b, and c are the true statements related to the genetic defect responsible for HD. Therefore, the correct answer is: f. a, b, and c only