Mendelism, Linkage and Crossing Over
Multiple Choice Questions and Answers
1. Mendelian combinations are due to
(a) independent assortment of genes
(b) linkage of genes
(c) mutation
(d) dominance
Answer: (a) independent assortment of genes
2. Blue colour in human is recessive to brown eye colour. The expected children of a marriage between a blue eyed woman and a brown eyed man who had blue eyed mother, would be
(a) all blue eyed
(b) all brown eyed
(c) one blue eyed and one brown eyed
(d) all black eyes
Answer: (c) one blue eyed and one brown eyed
3. Sexually reproducing organisms contribute to their offsprings
(a) half of their genes
(b) all the genes
(c) one fourth of their genes
(d) double the number of genes
Answer: (a) half of their genes
4. An individual with 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 Bb, it produces two kinds of the gametes B and b. The probability of b gamete fertilizing B or b is
(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 chosen by Mendel?
(a) 2
(b) 3
(c) 4
(d) 7
Answer: (a) 2
11. A cross between 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), 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 offsprings 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 pea is dominant over green pea. 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
20. 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%
21. When a heterozygous dominant is crossed with homozygous recessive, 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
22. Probability of four sons to a couple is
(a) 1/4
(b) 1/8
(c) 1/16
(d) 1/32
Answer: (c) 1/16
23. A gamete normally 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
24. Two crosses between the same pair of genotypes or phenotypes in which the sources of the gametes are reversed in one cross, is known as
(a) test cross
(b) reciprocal cross
(c) dihybrid cross
(d) reverse cross
Answer: (b) reciprocal cross
25. In codominance F1 hybrids show
(a) both dominant and recessive characters
(b) only dominant character
(c) only recessive character
(d) intermediate character between dominant and recessive
Answer: (a) both dominant and recessive characters
26. 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
27. 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 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.
28. Linkage was discovered by
(a) Blakeslee
(b) Sutton
(c) Muller
(d) Bateson
Answer: (d) Bateson
29. 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
30. Crossing over in diploid organism is responsible for
(a) Recombination of linked genes
(b) Segregation of alleles
(c) Dominance of genes
(d) Linkage between genes
Answer: (b) Segregation of alleles
31. A pair of genes may be called linked only if their recombination frequency in a test cross is
(a) higher than the expected value of 50%
(b) lower than the expected value of 50%
(c) equal to the expected value
(d) none of the above
Answer: (a) higher than the expected value of 50%
32. What will be the number of linkage groups in maize if it has 10 pairs of chromosomes?
(a) 5
(b) 10
(c) 20
(d) 30
Answer: (b) 10
33. A and B genes are linked. What shall be the genotype of progeny in a cross between ABab and aabb?
(a) AAbb and aabb
(b) AaBb and aabb
(c) AABB and aabb
(d) None
Answer: (c) AABB and aabb
34. When a cluster of genes show linkage behaviour they
(a) do not show a chromosome map
(b) show recombination during meiosis
(c) do not show independent assortment
(d) induce cell division
Answer: (c) do not show independent assortment
35. Crossing over that result in genetic recombination in higher organisms occurs between
(a) two different bivalents
(b) sister chromatids of a bivalent
(c) non sister chromatids of a bivalent
(d) two daughter nuclei
Answer: (c) non sister chromatids of a bivalent
36. Lack of independent assortment of two genes A and B in fruit fly Drosophila is due to
(a) crossing over
(b) repulsion
(c) recombination
(d) linkage
Answer: (d) linkage
37. Substitution of a purine nucleotide by pyrimidine nucleotide is known as
(a) transition
(b) transversion
(c) inversion
(d) transduction
Answer: (b) transversion
38. Trisomy has a chromosome complement of
(a) 2n-1
(b) 2n+3
(c) 2n+2
(d) 2n+1
Answer: (d) 2n+1
39. Which of the following is a base analogue?
(a) 5-bromouracil
(b) caffeine
(c) colchicine
(d) nitrous acid
Answer: (a) 5-bromouracil
40. A complete set of chromosomes inherited as a unit from one parent is called
(a) Genome
(b) Genotype
(c) Nucleoid
(d) Euploid
Answer: (a) Genome
41. The plant which made Hugo De vries famous is
(a) Antirrhinum majus
(b) Lathyrus odoratus
(c) Oenothera lamarckiana
(d) Pisum sativum
Answer: (c) Oenothera lamarckiana
42. Raphanobrassica is an example of
(a) trisomic
(b) allopolyploid
(c) autopolyploid
(d) amphidiploids
Answer: (b) allopolyploid
43. Datura is a classic example of
(a) euploidy
(b) monosomy
(c) trisomy
(d) inversion
Answer: (c) trisomy
44. Insertion or deletion of a single base causes
(a) inversion mutation
(b) transition mutation
(c) frame-shift mutation
(d) transversion mutation
Answer: (c) frame-shift mutation
45. The number of phenotypes in ABO blood group is
(a) 1
(b) 4
(c) 6
(d) 8
Answer: (b) 4
46. Mutations can be induced with
(a) ethylene
(b) gamma radiations
(c) infrared radiations
(d) IAA
Answer: (b) gamma radiations
47. Base substitution caused by base analogues is
(a) transition
(b) transversion
(c) complementation
(d) translocation
Answer: (a) transition
48. Cancer cells are most easily damaged by radiations than normal cells because they are
(a) non dividing
(b) starved of mutation
(c) undergoing rapid division
(d) different in structure
Answer: (c) undergoing rapid division
49. A nutritionally wild type of organism, which does not require any additional growth supplement is known as
(a) prototroph
(b) phenotroph
(c) holotype
(d) auxotroph
Answer: (d) auxotroph
50. What base is responsible for hot spots for spontaneous point mutations?
(a) 5-bromouracil
(b) 5-methyl cytosine
(c) adenine
(d) guanine
Answer: (d) guanine