The tendency of genes found on the chromosomes to stay intact and transfer it to the next generation successfully is linkage. Crossing over, on the other hand, is the exchange of chromosomal sections to derange already formed links to form newer linkages. Where linkages produce parental types, increasing in age with increasing linkage, crossing over produces recombinations which decrease with age
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1. Crossing over takes place in the
(a) Diakinesis stage
(b) Anaphase stage
(c) Pachytene stage
(d) Leptotene stage
Answer: (c)
2. There are 4 pairs of chromosomes in a Drosophila. The linkage groups present in it are
(a) one more than the pair of chromosomes
(b) one less than the pair of chromosomes
(c) four
(d) eight
Answer: (c)
3. Percentage of crossing over is more when
(a) genes are located in a different cell
(b) genes are not linked
(c) linked genes are located close to each other
(d) linked genes are located far apart from each other
Answer: (d)
4. If the percentage of crossing over between two genes is 10, then the distance between two genes will be
(a) 5 morganoid
(b) 10 centimorgans
(c) 20 centimorgans
(d) 40 map units
Answer: (b)
5. Alleles of different genes that are on the same chromosome can occasionally be separated by a phenomenon called
(a) crossing over
(b) continuous variation
(c) epistasis
(d) pleiotropy
Answer: (a)
6. Repulsion and coupling are two faces of
(a) mutation
(b) chiasmata
(c) linkage
(d) crossing over
Answer: (c)
7. If gene frequency between genes a and c is 2%; b and c is 13%; b and d 4%; a and b 15%; c and d 17 and a and d 19%. The sequence of genes in a chromosome is
(a) a,d,b,c
(b) d,b,a,c
(c) a,b,c,d
(d) a,c,b,d
Answer: (d)
8. This is the reason why Mendel did not recognize linkage phenomenon in his experiments
(a) he studied only pure plants
(b) he did not have a powerful microscope
(c) characters he studied were situated on different chromosomes
(d) many chromosomes to handle
Answer: (c)
9. In a linear chromosome map distance between 4 loci is as follows a-b is 10%, a-d is 3%, b-c is 4% and a-c is 6%. The crossover frequency between c and d is
(a) 4-12%
(b) 3-6%
(c) 9%
(d) 3%
Answer: (d)
10. Where does this evidence come from? – crossing over takes place at a four-stranded stage and not at two stranded stages of chromosomes.
(a) studies on linkage maps of chromosomes in Drosophila
(b) studies of meiosis in maize
(c) 4:4 organization of ascospores in Neurospora
(d) 2:2:2:2 organization of ascospores in Neurospora
Answer: (d)
11. Crossing over occurs between
(a) Non-sister chromatids of non-homologous chromosome at zygotene stage of prophase-I
(b) Non-sister chromatids of homologous chromosome at pachytene stage of prophase-I
(c) Non-sister chromatids of non-homologous chromosomes at pachytene stage of prophase I
(d) Non-sister chromatids of homologous chromosome at zygotene stage of prophase I
Answer: (b)
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