MCQ on Linkage and Crossing Over

 1. When a heterozygous dominant and homozygous recessive are crossed with each other , then the ratio in the next filial generation will be: 

(a) 1:2

(b) 2:1

(c) 3:1

(d) 1:1

Answer: (d) 1:1

 2. Probability of occurrence of four sons in a couple is

(a) 1/4

(b) 1/8

(c) 1/16

(d) 1/32

Answer: (c) 1/16

3. A gamete generally contains

(a) two alleles of a gene

(b) one allele of a gene

(c) many alleles of a gene

(d) all alleles of a gene

Answer: (b) one allele of a gene

4. An individual having two identical members of a pair of genetic factors is called

(a) heteromorphic

(b) heterozygote

(c) homomorphic

(d) homozygote

Answer: (d) homozygote

5. A plant is heterozygous and is designated as Bb. If it produces two kinds of the gametes B and b. The probability of b gamete fertilizing B or b will be

(a) 1/2

(b) 1/1

(c) 0/1

(d) 1/4

Answer: (b) 1/1

6. The plants are considered to be true breeding when

(a) all the plants of the parental generation resemble each other

(b) the progeny occupies less space

(c) the progeny may show genetic variability which may finally be utilised for evolving a better type

(d) the progeny is free of disease

Answer: (a) all the plants of the parental generation resemble each other

 7. Using two pairs-tall and dwarf and smooth and wrinkled seeds the principle of independent assortment of characters is proved by the

(a) observation that F1 progeny is tall

(b) appearance of tall and dwarf in 3:1 ratio and also the appearance of smooth and wrinkled seeded plants in 3:1 ratio in F2 population

(c) appearance of tall and dwarf plants in F2 population

(d) appearance of smooth and wrinkled seeded plants, F2 population

Answer: (b) appearance of tall and dwarf in 3:1 ratio and also the appearance of smooth and wrinkled seeded plants in 3:1 ratio in F2 population

 8. The percentage of ab gametes produced by AaBb parent will be

(a) 12.5

(b) 25

(c) 50

(d) 75

Answer: (b) 25

 9. Dominant gene for tallness is T and for yellow colour is Y. If a plant heterozygous for both the traits is selfed, then the ratio of pure homozygous dwarf and green offsprings would be

(a) 1/4

(b) 4/16

(c) 3/16

(d) 1/16

Answer: (d) 1/16

 10. How many pairs of contrasting characters in pea pod were considered by Mendel in this cross?

(a) 2

(b) 3

(c) 4

(d) 7

Answer: (a) 2

 11.  A cross between an F1 hybrid and a recessive parent gives the ratio of

(a) 3:1

(b) 1:1

(c) 2:1

(d) 4:1

Answer: (b) 1:1

 12. If a homozygous tall male plant (dominant) is crossed with a homozygous dwarf male plant (recessive), the genotype of endosperm would be

(a) ttt

(b) ttT

(c) TTt

(d) TTT

Answer: (c) TTt

 13. How many types of genetically different gametes would be produced by a heterozygous plant having the genotype AABbCc

(a) 2

(b) 4

(c) 6

(d) 9

Answer: (b) 4

 14. The genes controlling 7 traits in pea studied by Mendel were later found to be located on how many chromosomes?

(a) 7

(b) 4

(c) 5

(d) 6

Answer: (b) 4

 15. In a monohybrid cross red colour of flower (RR) is dominant over white colour of flower (rr). What will be the phenotypic ratio of the offspring from a cross between Rr x rr parents?

(a) 50% red and 50% white

(b) 75% red and 25% white

(c) 100% red

(d) 100% white

Answer: (a) 50% red and 50% white

 16. If a dwarf plant was treated with gibberellic acid, it grew as tall as the pure tall plant. If this treated plant is crossed with pure tall plant, then the phenotypic ratio of F1 generation is likely to be

(a) 50% dwarf and 50% tall

(b) 75% tall and dwarf 25%

(c) all dwarf

(d) all tall

Answer: (d) all tall

17. The universally applicable law of Mendel is

(a) law of dominance

(b) law of unit characters

(c) law of segregation

(d) law of independent assortment

Answer: (c) law of segregation

18. Genotypic and phenotypic ratios are same in

(a) a cross involving sex linked traits

(b) a test cross

(c) monohybrid cross in which homozygous dominant alleles become lethal

(d) none of these

Answer: (b) a test cross

19. In pea plants, yellow peas are dominant over green peas. Give the genotype of all plants that could possibly produce green peas when crossed with a heterozygote.

(a) YY and yy

(b) yy and YY

(c) Yy and Yy

(d) Yy

Answer: (c) Yy and Yy

 21. In a dihybrid cross what percentage of F1 progeny are obtained for both the traits?

(a) 8%

(b) 12.5%

(c) 25%

(d) 50%

Answer: (b) 12.5%

 22. In codominance F1 hybrids show

(a) both dominant and recessive characters

(b) only dominant character

(c) only recessive character

(d) the intermediate character between dominant and recessive

Answer: (a) both dominant and recessive characters

23. In case of incomplete dominance in F2 generation

(a) genotypic ratio 3:1

(b) phenotypic ratio is 3:1

(c) genotype ratio is equal to phenotypic ratio

(d) nothing can be concluded

Answer: (b) phenotypic ratio is 3:1

 24. Which of the following statements about crossing-over is most correct?

(a) There are as many crossings over possibilities as there are genes on the chromosome.

(b) The farther apart are the two genes on the chromosome, greater are the chances of their crossing over.

(c) Genes placed linearly adjacent on a chromosome have the greatest chances of crossing over

(d) crossing over does not occur at a distance of more than 5 map units

Answer: (b) The farther apart are the two genes on chromosome, greater are the chances of their crossing over.

 25. Linkage was discovered by

(a) Blakeslee

(b) Sutton

(c) Muller

(d) Bateson

Answer: (d) Bateson

 26. Often two genes do not assort independently as predicted by Mendel’s principle of independent assortment. However, even in such linked genes, linked it is never complete because of

(a) crossing over

(b) the phenomenon of dominance

(c) inversions

(d) certain enzymes which cleave DNA between two genes

Answer: (a) crossing over