This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Homologous DNA Recombination”.
1. Homologous DNA recombination in prokaryotes take place for________________
a) Increasing variability
c) Incorporation of gene
d) Taking up a plasmid from media
Explanation: In prokaryotes, the repair is mainly the sole recombination as these organisms have only one copy of chromosomes. Two copies are available only during fission when this recombination takes place. Gene transfer processes and their incorporation are very rare.
2. If an organism has 8 chromosomes in diploid condition, what will be the number of chromosomes after telophase of meiosis 1?
Explanation: In meiosis 1 there is 1st doubling of the chromosomes which are then distributed in two cells at its end. These are then further distributed in two cells leading to their number becoming half. Thus after 1st meiosis the number should be 8.
3. If there are 2 strands of chromosomes that can pair with a single strand, and they are both paired to the same strand, their junction is called_______________
c) Double binding
d) Branch point
Explanation: The point where the two strands complementary to a single strand meet is known as a branch point. Chimera is a protein made by combining domains from two different proteins.
4. Holliday intermediate could be mistaken for ___________ under microscope.
a) Hetero chromatin
b) Circular plasmid
c) Linear extracellular chromosome
d) Broken chromosome
Explanation: Circular chromosomes can appear as Holliday intermediate as when they are twisted the twist points may appear as crossing over sites.
5. How many Rec A are present in one turn around the single stranded chromosome?
Explanation: 6.2 monomers of Rec A are necessary for one turn around the central chromosome. They form a right handed alpha helix around the chromosome.
6. Rec A doesn’t____________________
a) Line up the homologous chromosome with the one it surrounds
b) Perform spooling
c) Cleaves at recombination site
d) Help in branch migration
Explanation: Rec A helps to take up the homologous chromosome from the media and it aligns it in a manner helping in recombination. It also helps in branch migration but it plays no role in cleaving the DNA.
7. The Ruv A of the resolvosome complex binds at________
a) On each chromosome on either side of branch point
b) At the branch point
c) After exchange
d) At the terminals
Explanation: While Rub B binds on other side of the branch point aiding in branch migration, Ruv A binds at the Chi structure stabilizing it.
8. In single stranded nick__________
a) The 3’-OH end of the nick invades other complete strands
b) Both the strands undergo fork regression
c) The nick is treated like an okazaki fragment point
d) The nick is bypassed without repair
Explanation: In single stranded nick the 5’ end of the nick forms the base pair and normal DNA strand with the available strand but the 3’ end has to invade the 5’ end to bypass the nick. In this bypass the nick is repaired and not left as it is.
9. In case of chicken foot Holliday intermediate, the template strand for synthesis across lesion is___________
a) The parent strand aligned along strand with lesion
b) The parent strand aligned against lesion strand
c) The daughter strand with lesion
d) The daughter strand without lesion
Explanation: In this model to bypass the lesion the daughter strand synthesized from the other parent strand is used as a template. This codes for the correct bases against the lesion and is made possible by fork regression.
10. Recombination occurs in ______________
Explanation: Pachytene stage in prophase 1 of meiosis is when the recombination takes place. This is after the formation of a synaptonemal complex in zygotene when synapsis occurs.
Sanfoundry Global Education & Learning Series – Cytogenetics.
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