Question

1. Homologous recombination can happen between non-identical DNA sequences. T/F?

2. Homologous recombination can happen in_______

a) meiosis b) mitosis c) both

3. Homologous recombination in meiosis has the main purpose of_____

a) DNA repair b) Creating new chromosomes   c) Sealing double-stranded breaks

4. Strand invasion usually happens without enzymatic assistance. T/F?

5. When replication fork runs into a nick, it results in a_______

a) single-stranded break b) double-stranded break

6. The invading end is usually a _______

a) 3' end b) 5' end c) both are possible

7. DNA repair of broken replication fork by homologous recombination uses _______ as a template.

a) sister chromatid b) homologous chromosome

8. The extension of the paired region formed by invading strand is called______

a) Strand invasion b) Branch migration

9. A complex formed between two meiotic chromosomes just after strand invasion and sealing the gaps is called __________

a) crossover b) Holliday junction   c) Both mean the same thing

10. Resolution of a Holliday junction always results in crossovers. T/F?

11. Gene conversion due to homologous recombination happens with participation of ______

a) Base excision repair b) Nucleotide excision repair   c) mismatch repair

12. Homologous recombination between direct repeats on the same chromosome results in_____

a) duplication b) deletion c) inversion

13. Homologous recombination between inverted repeats on the same chromosome results in ______

a) duplication b) deletion c) inversion

14. Which type of the transposable element uses transposase?

a) DNA transposons b) retrotransposons

15. Reverse transcription enzyme, other than telomerase, is coded in eukaryotic genome. T/F?

16. Cut and paste transposition generates multiple copies of transposons. T/F?

17. Cut and paste transposition involves______

a) Reverse transcriptase b) Transposase c) both

18. Transposase can_______

a) Cut transposon out b) Insert transposon into a new location c) It can do both

19. Some retrotransposons are still moving in the human genome. T/F?

Answer 1

1. Homologous recombination can happen between two non-identical DNA sequences. True. Homologous recombination is a process which involves the exchange of genetic segment between identical and non-identical DNA sequences. Sister chromatids of a chromosome share identical DNA sequences whereas homologous chromosomes are similar to each other but not identical as in homologous pair of chromosome one come from mother and other from father.

2. Homologous recombination can happen in Both (option "c"). Homologous recombination occurs during the cell division of both kinds, mitosis as well as meiosis. During mitosis, homologous recombination helps in DNA repair which occurred due to DNA damaging agents or environmental factors. DNA repair is important for proper functioning of cells as change in genetic information due to DNA damage may lead to lethal effects. During meiosis homologous recombination is responsible for genetic variation by facilitating cross-over between chromosomes when homologous chromosomes are aligned together. Genetic variation is important for evolution.

3. Homologous recombination in meiosis has the main purpose of creating a new chromosome (option "b"). During meiosis after homologous chromosome pairing, similar segments of chromosome undergo exchange with each other which results in new combination of genes of the chromosome and causes genetic variation among the populations.

4. Strand invasion generally happens without enzymatic assistance. True. During the process of homologous recombination when double-stranded DNA break occurs, after the resection, RPA (Replication protein A) protein which has a higher affinity for single-stranded DNA form a nucleoprotein filament with the help of other proteins. This single-stranded DNA which is coated with RPA invades into the similar/ identical DNA duplex and the process is known as strand invasion.