ASRB NET and ARS / SMS / STO (Agricultural Scientists Recruitment Board) · India · Agricultural Scientists Recruitment Board
Original practice questions written to the published syllabus · not past papersSelection and mating systems that improve herds and flocks, sire evaluation, genomic selection and the conservation of animal genetic resources.
In the exams: ICAR AICE-JRF core group 05; ICAR AIEEA-PG 14 (AGB); EGEL Plus reproduction and genetics 15
How our questions for ASRB NET and ARS / SMS / STO spread across the units of Livestock & Poultry Breeding. Difficulty: 26 easy, 45 medium, 29 hard.
| Response to selection | 10 | |
| Inbreeding | 10 | |
| Outbreeding and crossbreeding | 10 | |
| Heterosis | 9 | |
| Genomic selection | 9 | |
| Selection index | 8 | |
| Selection experiments | 8 | |
| Sire evaluation and progeny testing | 8 | |
| Laboratory animal breeding | 8 | |
| Breeding strategies and national breeding policy | 7 | |
| Conservation of animal genetic resources | 7 | |
| Methods of selection | 6 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In a pig herd, mean body weight at 180 days is 90 kg. The boars and gilts selected as parents (mass selection in both sexes) average 102 kg at the same age. Heritability is 0.25. The expected response in the next generation is:
A. 3.0 kg
S = 102 − 90 = 12 kg. R = h²S = 0.25 × 12 = 3.0 kg. Multiplying h² by the selected mean (25.5) or by the herd mean (22.5) uses the wrong basis; 12 kg is the selection differential, not the response.
The reduction in additive genetic variance caused by selection itself, through negative covariances (gametic phase disequilibrium) between loci among selected parents, is known as the:
D. Bulmer effect
Bulmer (1971) showed that selection creates negative disequilibrium between loci, lowering additive variance in the next generation until equilibrium. The Hill–Robertson effect concerns interference between linked loci under selection in finite populations; the Wahlund effect is the deficit of heterozygotes when subpopulations are pooled.
The selection index was first applied to animal breeding by:
D. L.N. Hazel (1943)
Smith (1936) introduced the discriminant function for plant selection; Hazel (1943) developed the index for animals using genetic and phenotypic parameters. Henderson developed BLUP; Wright developed path coefficients and the inbreeding coefficient.
Over six generations of selection for litter weight, the cumulative selection differential was 150 g and the cumulative response (measured against a control line) was 45 g. The realised heritability is:
A. 0.30
Realised h² = cumulative response / cumulative selection differential = 45/150 = 0.30. Inverting the ratio gives 3.33, impossible for a heritability; dividing again by the number of generations (0.050) double-counts time, since both totals already span six generations; 0.23 wrongly divides by S + R (45/195).
In a population with effective size 25, Robertson's theory gives the maximum half-life of response to selection (the number of generations to reach half the limit) as about:
A. 35 generations
Half-life is at most about 1.4Ne generations: 1.4 × 25 = 35. 50 is 2Ne, the multiplier for total response; 12.5 is Ne/2; 70 multiplies 1.4 by 2Ne instead of Ne.
A sire whose own inbreeding coefficient is 0.25 is mated to his own daughter (out of an unrelated dam). The inbreeding coefficient of the offspring is:
D. 0.3125
The sire is the common ancestor; n1 = 0 (he is the sire) and n2 = 1 (his daughter is the dam). F = (½)^(0+1+1) × (1 + 0.25) = 0.25 × 1.25 = 0.3125. 0.25 ignores the sire's own inbreeding; 0.375 would be the second generation of full-sib mating; 0.50 confuses F with the parent–offspring relationship.
The contemporary comparison method of sire evaluation was introduced in the United Kingdom by:
D. Robertson and Rendel (1954)
Robertson and Rendel compared each daughter with contemporary heifers by other sires in the same herd and season. Henderson developed BLUP; Hazel the selection index; Lush wrote the foundational text Animal Breeding Plans.
Compared with lactation models, test-day models in dairy sire and cow evaluation:
C. Use individual test-day milk records and account for the environment of each test day
Test-day models analyse each recording separately, allowing for the specific herd-test-date environment and making use of incomplete lactations, which improves accuracy. They include herd effects.
The accuracy of genomic predictions declines over generations if the reference population is not updated, mainly because:
C. Candidates become less related to the reference animals and marker–gene associations decay through recombination
Genomic prediction depends on linkage disequilibrium and relationships between candidates and the reference; both erode with recombination and distance of relationship. Adding new phenotyped animals to the reference each generation keeps accuracy up.
N'Dama cattle of West Africa are an important genetic resource mainly because of their:
B. Trypanotolerance
N'Dama and West African Shorthorn cattle tolerate trypanosome infection in tsetse areas, an adaptation that is hard to recreate and a key reason for conserving them.
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