Crossing over or Recombinant is the mutual exchange of segments between non-sister chromatids of homologous chromosomes. Bivalent may remain in the pachytene stage for days and dense area of about 100 nm appear here and there on bivalent which is believed to be the sites rich in enzymes required for crossing over. These dense regions are called recombinant nodules. if the separated segments of non-sister chromatids exchange their position, they get united by means of reannealing or R-protein. This type of exchange of segments brings about chromosome recombination. So, take this quiz and check your knowledge about crossing over or recombinant.
1. Who discovered crossing over?
A. Miller
B. Porter
C. Frans Alfons Janssens
D. Thomas Hunt Morgan
2. Crossing over takes place by breakage and reunion of ......
A. Genes
B. Chromosome
C. Chromatid segments
D. All of these
3. Which enzyme causes breakage or nicking of chromatid segments?
A. Ligase
B. Amylase
C. Endonuclease
D. Maltase
4. The frequency of crossing over increases with the increase in the _____ between two genes.
A. Age
B. Distance
C. Chemical
D. Inteference
5. Crossing over decreases with the increase in .....
A. Distance
B. Chemicals
C. Interference
D. Age
6. In which organism, males have a low frequency for crossing over?
A. Cat
B. Dog
C. Rat
D. Elephant
7. Which of the following increases the frequency of crossing over?
A. X-rays
B. Temperature
C. Both of them
D. None of these
8. Which one is inversely proportional to the distance between the points of crossing over?
A. Distance
B. Age
C. Temperature
D. Interference
9. A pair of a gene may be identified as linked if their recombination frequency in a test cross progeny....
A. More than 50%
B. More than 75%
C. Less than 50%
D. Less than 75%
10. Which enzyme acts as a molecular glue of the cell?
A. Endonuclease
B. Exonuclease
C. Maltose
D. Ligase
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