MCQs on Linkage and Crossing Over For NEET 2020

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

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 morgan

(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)

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