Animal Genetics and Breeding- ICAR JRF/SRF 2024

• Assertion (A) is Correct: Heritability ($h^2$) in quantitative genetics is the proportion of total phenotypic variation ($V_P$) in a population that is attributable to genetic variation ($V_G$ in the broad sense, or additive genetic variance $V_A$ in the narrow sense):

• Reason (R) is Correct: Heritability is not a biological constant of an individual or species; it is a population-specific parameter that depends strictly on the genetic background of the specific population and the specific environmental variance ($V_E$) under which the animals are managed:

Changes in environmental control or allele frequencies directly alter $h^2$.

• Explanation: (R) correctly explains why heritability estimates vary across herds, seasons, and management systems.

• Gene Pool: The total collection of all genes and alleles present in a breeding population at a given time is termed the gene pool.
• Related Genetic Concepts:
• Genotype: The specific allelic constitution of an individual organism at one or more loci.
• Phenotype: The observable physical, physiological, or biochemical characteristics of an individual resulting from its genotype interacting with the environment ($P = G + E$).
• Breeding Value ($A$): The value of an individual's genes judged by the mean phenotypic value of its progeny; represents the sum of the average effects of the genes it transmits to offspring.

Correct option: (1) Gene Pool

• cDNA Library Construction Sequence:

• Elution of mRNA: Total cellular RNA is isolated, and mature polyadenylated mRNA is selectively purified using oligo(dT) cellulose affinity chromatography.
• Action of Reverse Transcriptase: Reverse transcriptase synthesizes a complementary DNA strand (cDNA) from the mRNA template using an oligo(dT) primer, followed by second-strand DNA synthesis.
• Incorporate cDNA into Vector: Double-stranded cDNA is ligated with linkers/adaptors and inserted into a cloning vector (e.g., plasmid or bacteriophage $\lambda$).
• Clone cDNA: Recombinant vectors are transformed into host cells (e.g., E. coli) and propagated as individual cDNA clones.
  • Correct Chronological Sequence: (D) $\to$ (B) $\to$ (C) $\to$ (A).