• 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

• Reproductive Parameters of Laboratory Mice (Mus musculus):
• Puberty onset (vaginal opening in females, testicular descent in males) occurs around 4–6 weeks of age.
• Full sexual maturity and optimal breeding age is reached at 6–8 weeks of age (body weight $\approx 20-25\text{ g}$).
• Breeding prior to 6 weeks is avoided to prevent small litter sizes and poor maternal behavior.
• nalysis:
• (6-8 week): Correct physiological age at sexual maturity.

Correct option: (2) 6-8 week

• Genetic Basis of Heterosis (Hybrid Vigor):
• According to Falconer & Mackay's quantitative genetics framework:
• When two inbred parental lines differing in gene frequencies ($p_1$ and $p_2$, where $y = p_1 - p_2$) are crossed:
• The amount of heterosis observed in the $F_1$ generation (the deviation of $F_1$ from the mid-parent value) summed across all loci is:

where:

• $d$ = dominance deviation at the locus
• $y = p_1 - p_2$ = difference in allele frequency between the two parental populations
• Heterosis strictly depends on the presence of dominance ($d$) and genetic divergence ($y^2$) between parental lines.
• nalysis:
• (dy^2): Correct formula ($dy^2$, OCR recorded as dy).

Correct option: (2) dy