Question

If the cytosine in the sequence TCAT is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication?

(a) TTAT
(b) TUAT
(c) TGAT
(d) TAAT

Answer 1

After two rounds of replication following cytosine deamination in the sequence TCAT, without repair, the final mutated sequence in the DNA would be TTAT, which is a G-C to A-T point mutation.

Step-by-step explanation:

If the cytosine in the sequence TCAT is deaminated and not repaired, the cytosine (C) would be converted into uracil (U). However, during DNA replication, uracil pairs with adenine (A) instead of the original guanine (G) that cytosine pairs with. After the first round of replication, you would get one strand with the uracil (TUAT) and one with the adenine as its pair (TAAT). Following a second round of replication, the uracil containing strand would produce a thymine-adenine pair (TTAT), while the adenine containing strand would produce a adenine-thymine pair as before (TAAT).

Therefore, the mutation observed after two rounds of replication would be replacing a G-C base pair with an A-T base pair, resulting in the DNA sequence TTAT, which is option (a).