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Free Animal Breeding and Genetics MCQs with Answers

60 Animal Breeding and Genetics MCQs from Veterinary Science, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Covers genes, chromosomes, inheritance, genetic variation, mutations, heritability and quantitative traits in livestock. It also includes selection methods, breeding systems, inbreeding, crossbreeding, heterosis and evaluation of traits such as growth, milk yield, fertility and disease resistance.

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60 questions · page 1 of 3

1. Narrow-sense heritability of a quantitative trait is the proportion of phenotypic variance due to which component?

  • A. Additive genetic variance
  • B. Dominance genetic variance
  • C. Permanent environmental variance
  • D. Temporary environmental variance

Explanation: Narrow-sense heritability is additive genetic variance divided by phenotypic variance.

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Correct answer: Additive genetic variance

2. In animal breeding, the inbreeding coefficient of an individual represents the probability that two alleles at a locus are:

  • A. Identical by mutation
  • B. Identical by descent
  • C. Different in origin
  • D. Dominant in expression

Explanation: The inbreeding coefficient is the probability that the two alleles inherited by an individual are identical by descent.

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Correct answer: Identical by descent

3. Heterosis in a crossbred animal is usually measured as the superiority of its performance over the:

  • A. Performance of the older parent breed
  • B. Performance of the poorer parent breed
  • C. Average performance of its parent breeds
  • D. Average performance of unrelated purebreds

Explanation: Heterosis, or hybrid vigour, is commonly calculated by comparing crossbred performance with the average of the two parental breed…

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Correct answer: Average performance of its parent breeds

4. Which method estimates the breeding value of a young sire mainly from the performance of his offspring?

  • A. Pedigree recording
  • B. Mass selection
  • C. Phenotypic grading
  • D. Progeny testing

Explanation: Progeny testing evaluates a sire by studying the performance of many offspring produced with different dams.

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Correct answer: Progeny testing

5. If two cattle are both known carriers of an autosomal recessive lethal allele, what proportion of their offspring is expected to be affected?

  • A. 25 percent
  • B. 50 percent
  • C. 75 percent
  • D. 100 percent

Explanation: A carrier by carrier mating has expected genotypes of 25 percent affected homozygotes, 50 percent carriers, and 25 percent normal…

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Correct answer: 25 percent

6. A trait has a heritability of 0.25 and the selection differential is 4 units. Using the breeder's equation, what response to selection is expected?

  • A. 0.5 units
  • B. 1 unit
  • C. 4 units
  • D. 16 units

Explanation: The response is calculated as R = h² × S. Therefore, R = 0.25 × 4 = 1 unit, assuming the heritability and selection differential are…

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Correct answer: 1 unit

7. What is the diploid chromosome number of domestic cattle?

  • A. 54
  • B. 60
  • C. 64
  • D. 78

Explanation: Domestic cattle have a diploid chromosome number of 60, arranged in 30 pairs.

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Correct answer: 60

8. Repeatability of a trait includes the effects of permanent environment in addition to which genetic component?

  • A. Only sex-linked variance
  • B. Only mutation variance
  • C. Only temporary environment
  • D. Additive genetic variance

Explanation: Repeatability includes additive genetic effects and permanent environmental effects that continue to influence repeated records.

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Correct answer: Additive genetic variance

9. In birds, which statement correctly describes the usual sex chromosome arrangement?

  • A. Males are ZZ and females are ZW
  • B. Males are ZW and females are ZZ
  • C. Males are XX and females are XY
  • D. Males are XY and females are XX

Explanation: Birds generally have ZZ males and ZW females. Thus, the female is the heterogametic sex because her eggs carry either a Z or a W chromosome.

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Correct answer: Males are ZZ and females are ZW

10. In a population at Hardy-Weinberg equilibrium, a recessive phenotype occurs in 9 percent of individuals. What is the expected frequency of heterozygous carriers?

  • A. 21 percent
  • B. 30 percent
  • C. 42 percent
  • D. 49 percent

Explanation: The recessive phenotype frequency is q² = 0.09, so q = 0.3 and p = 0.7. The carrier frequency is 2pq = 2 × 0.7 × 0.3 = 0.42, or 42 percent.

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Correct answer: 42 percent

11. Which genetic effect is transmitted predictably from a parent to its offspring and forms the main basis of breeding value?

  • A. Epistatic gene effect
  • B. Dominance gene effect
  • C. Additive gene effect
  • D. Environmental effect

Explanation: Additive gene effects are the average effects of individual alleles and are transmitted predictably to progeny.

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Correct answer: Additive gene effect

12. A mating between close relatives increases homozygosity primarily because it increases the chance that offspring receive:

  • A. Extra chromosome copies
  • B. New alleles by mutation
  • C. Different alleles at each locus
  • D. Identical alleles by descent

Explanation: Related parents are more likely to carry copies of the same ancestral allele.

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Correct answer: Identical alleles by descent

13. The main purpose of a progeny test in dairy cattle is to evaluate a sire by examining the performance of his:

  • A. Daughters
  • B. Parents
  • C. Siblings
  • D. Mating partners

Explanation: A dairy sire is commonly evaluated through the milk production of many daughters because daughters inherit half of their genes from him.

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Correct answer: Daughters

14. Which genetic parameter describes the correlation between an animal's performance for the same trait measured on different occasions?

  • A. Heritability
  • B. Repeatability
  • C. Genetic correlation
  • D. Phenotypic variance

Explanation: Repeatability is the correlation between repeated records of the same trait in an individual.

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Correct answer: Repeatability

15. When two genes are located close together on the same chromosome, they are most likely to show:

  • A. Complete dominance
  • B. Independent assortment
  • C. Genetic linkage
  • D. Random mutation

Explanation: Genes positioned close together on one chromosome tend to be inherited together, a phenomenon called genetic linkage.

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Correct answer: Genetic linkage

16. A bull is heterozygous for a recessive autosomal coat colour allele. If he is mated with a homozygous dominant cow, the expected offspring are:

  • A. Three quarters dominant and one quarter recessive
  • B. Half recessive and half dominant
  • C. All phenotypically recessive
  • D. All phenotypically dominant

Explanation: The bull produces dominant and recessive gametes, while the homozygous dominant cow produces only dominant gametes.

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Correct answer: All phenotypically dominant

17. Which breeding strategy is specifically designed to exploit both breed complementarity and hybrid vigour?

  • A. Crossbreeding
  • B. Close breeding
  • C. Pure breeding
  • D. Random mating

Explanation: Crossbreeding combines desirable characteristics from different breeds and can produce heterosis in the crossbred progeny.

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Correct answer: Crossbreeding

18. Effective population size is usually smaller than the census population size when:

  • A. All animals breed equally
  • B. The sex ratio is unequal
  • C. Mating is completely random
  • D. Generations overlap equally

Explanation: An unequal number of breeding males and females reduces the effective population size because fewer individuals contribute genes equally…

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Correct answer: The sex ratio is unequal

19. In a sex linked recessive disorder carried on the X chromosome, a carrier female mated with a normal male is expected to produce affected offspring mainly among the:

  • A. Both sexes equally
  • B. Female offspring
  • C. Male offspring
  • D. Only maternal offspring

Explanation: Males receive their single X chromosome from their mother, so sons who inherit the recessive allele are affected.

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Correct answer: Male offspring

20. Which measure is most directly used to express the genetic merit of an animal for selection purposes?

  • A. Generation interval
  • B. Phenotypic record
  • C. Selection differential
  • D. Estimated breeding value

Explanation: Estimated breeding value predicts the additive genetic merit that an animal can transmit to its offspring.

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Correct answer: Estimated breeding value
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