m13,14,15 - ebnalfady

[ArchivalUser]

13. Patients with hereditary nonpolyposis colon cancer [HNPCC (114500)] have genes with microsatellite instability, that is, many regions containing abnormal, small loops of unpaired DNA. This is a result of a mutation affecting
a. Mismatch repair
b. Chain break repair
c. Base excision repair
d. Depurination repair
e. Nucleotide excision repair

14. If a completely radioactive double-stranded DNA molecule undergoes two rounds of replication in a solution free of radioactive label, what is the radioactivity status of the resulting four double-stranded DNA molecules?
a. Half should contain no radioactivity
b. All should contain radioactivity
c. Half should contain radioactivity in both strands
d. One should contain radioactivity in both strands
e. None should contain radioactivity

15. Sickle cell anemia (141900) is the clinical manifestation of homozy¬gous genes for an abnormal hemoglobin molecule. The mutation in the β chain is known to produce a single amino acid change. The most likely mechanism for this mutation is
a. Crossing over
b. Two-base insertion
c. Three-base deletion
d. Nondisjunction
e. Single-base substitution (point mutation)

[ArchivalUser]

13-c/e
14-b
15-e

[ArchivalUser]

13 A
14 D
15 E

[ArchivalUser]

A
A
E

[ArchivalUser]

a
a
e

[ArchivalUser]

a
d
e

[ArchivalUser]

13: a
14: c could you please explain
15: e