Animal Genetics and Breeding- ICAR JRF/SRF 2024

• Breeding Value ($A$) in Quantitative Genetics:
• The breeding value of an individual represents the value of its genes transmitted to its offspring.
• Formally defined by Falconer & Mackay as the sum of the average effects of the alleles an individual carries across all loci influencing the quantitative trait:

• In terms of progeny testing, an individual's breeding value equals twice the expected mean deviation of its progeny from the population mean when mated randomly to a representative sample of the population.
• nalysis:
• (Sum of the average effect of alleles): Correct fundamental definition of breeding value.
• & 3: Progeny deviation is half the breeding value, not equal to or twice.

Correct option: (1) Sum of the average effect of alleles

• Approach to Hardy-Weinberg Equilibrium for Sex-Linked (X-Linked) Genes:
• Because heterogametic males ($XY$) receive their single X chromosome exclusively from their mother, whereas homogametic females ($XX$) receive one X from each parent:
• In each successive generation of random mating, the difference in allele frequency between males ($q_m$) and females ($q_f$) is:

• Thus, the difference between the frequencies in the two sexes is half the difference in the previous generation, but in the opposite direction, oscillating in a damped harmonic series until converging to equilibrium:

• nalysis:
• Correct mathematical description of sex-linked allele frequency dynamics.

Correct option: (4) is half the differences in the previous generation, but in other direction

• Wright's Coefficient of Relationship ($R$):
• Defined as the proportion of genes shared identical by descent between two relatives:

where $L$ is the number of steps in each genealogical path through a common ancestor.

• Single First Cousins: Share 2 common grandparents through 1 set of siblings:

• Double First Cousins: Two siblings of one family marry two siblings of another family. Their children share all 4 grandparents through 4 independent paths:

• nalysis:
• (0.25): Correct.

Correct option: (3) 0.25

• Dispersive Forces in Population Genetics: Dispersive forces are non-directional evolutionary processes operating in small, finite populations that lead to random fluctuations in allele frequencies. The primary dispersive force is random genetic drift (sampling variance of gametes).
• Subpopulation Uniformity and Differentiation: As isolated subpopulations experience random genetic drift, genetic variance within each subpopulation declines (leading towards fixation or loss of alleles, i.e., uniformity within subpopulations), while genetic differentiation among different subpopulations increases ($F_{ST} \gt 0$).
• Systematic Forces vs. Dispersive Forces:
• Systematic Forces: Selection, mutation, and migration change gene frequencies in a predictable, directional manner with deterministic rates.
• Dispersive Forces: Random genetic drift and sampling effects act unpredictably in direction but predictably in magnitude based on effective population size ($N_e$). Thus, (C) and (D) characterize dispersive processes.

Correct option: (4) (C) and (D) only.

• Postulation of Hardy-Weinberg Law: The Hardy-Weinberg law (or equilibrium) was independently formulated in 1908 by the British mathematician G. H. Hardy and the German physician Wilhelm Weinberg.
• Fundamental Principle: In a large, randomly mating population with negligible mutation, migration, selection, and genetic drift, allele and genotype frequencies remain constant from generation to generation:

where $p$ and $q$ represent the frequencies of alleles $A$ and $a$, respectively.

• Significance in Animal Genetics: It provides the baseline theoretical null model to test evolutionary forces and determine whether a livestock population is under selection or random mating.

Correct option: (2) 1908