32. Double-stranded breaks have been introduced into the DNA by exposure to X-rays. Repair is initiated, with strand invasions making a branched intermediate. How can this intermediate be resolved?

a)            Resolution of the branched intermediate can occur by synthesis-dependent strand annealing. This involves dissociation of the invading strancls and reannealing with their original complements. Gaps are filled in by DNA polymerase, and the DNA is sealed by ligase.

b)            Resolution of the branched intermediate can proceed by double-strand break repair. This involves dissociation of the invading strands and reannealing with their original complements. Gaps are filled in by DNA polymerase, and the DNA is sealed by ligase.

c)            Resolution of the branched intermediate can proceed by translesion DNA synthesis.

d)            Resolution of the branched intermediate can proceed by fork regression followed by digestion of the short arm and reloading of the repl isome.

e)            All of the answers are correct.

32. Aneuploidy:

a)            a condition in which a cell has the wrong number of chromosomes

b)            can be caused by misalignment of chromosomes during meiosis I.

c)            can be caused by incomplete recombination during meiosis I.

d)            is the leading genetic cause of developmental and mental disabilities.

e)            All of the answers are correct.

42. When the replication machinery encounters a single-strand break, the replication fork collapses resulting in a double-strand break. Which of the following would be the FOURTH step in repairing this damage?

a)       The 3′ single-strand overhang invades the intact portion of the chromosome, pairs with its complementary strand, and displaces the other.

b)       Once the strand invasion is complete, branched migration occurs.

c)       The broken ends are processed, with the 5′ ending strand selectively degraded to create 3′ overhangs.

d)       Branch migration creates Holliday intermediates that are resolved by the enzyme resolvase.

Resol ution of the Holliday intermediate is followed by ligation and replication is restarted.