Question

3. In an organism, the genes TART and SWEET flank a single nucleotide polymorphism that could be found as either lemon or lime. The chromosome that contained the genotype grapefruit/lemon/pear was damaged by UV radiation. The cell proceeded to repair the damage, which lead to the formation of the following structure. TART SWEET х grapefruit lemon pear y = y starfruit lime apples (a) What DNA repair pathway was used to create the above structure? (0.5 point) (b) To resolve a Holliday junction, there are two ways to cut the DNA: cut at site x or y. Choose a combination of cut sites by circling the letter for the cut site at each junction. Left Holliday Junction: Right Holliday Junction: ( Kor Y X or (c) What are the genotypes of the two double stranded DNA strands following the damage repair and Holliday junction resolution? Use the combination you choose above (should have 4 total strands drawn). (1.5 points)

Answer 1

Answer 3a:)

The DNA damage caused by UV radiation is repaired by the nucleotide excision repair mechanism. A nuclease enzyme identifies and removes a segment of DNA comprising the lesion. Then, the polymerase introduces the correct bases and enzyme ligase seals the gap.

Answer 3b:)

To resolve the holiday junction, cut the X site of the left-hand junction and Y-site of the right-hand junction.

Answer 3c:)

This will produce the following 4 strands:

grapefruit lemon pear

grapefruit lemon pear

startfruit lime apples

startfruit lime apples

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