(a) Recurrent selection and Reciprocal recurrent selection. 10 (b) Which are the processes preventing random assortment of genes…

(a) Recurrent Selection and Reciprocal Recurrent Selection

Recurrent selection is a breeding strategy involving repeated cycles of selection and intermating within a single population. In each cycle, superior individuals are selected based on phenotypic performance, mated together, and their offspring form the base for the next generation. This method effectively increases the frequency of favorable alleles, leading to steady genetic gain for traits with moderate to high heritability. It is particularly useful for improving overall population mean without requiring external germplasm.

Reciprocal Recurrent Selection (RRS), however, involves the simultaneous improvement of two distinct populations. Here, candidates from Population A are test-crossed to Population B (and vice versa); they are selected on the performance of their crossbred progeny, and the selected parents are then intermated within their own population to form the next cycle. The key distinction is that RRS exploits both General Combining Ability (GCA) and Specific Combining Ability (SCA). By using each population as a tester for the other, RRS identifies heterosis (hybrid vigor) potential. While simple recurrent selection improves within-population performance, RRS is superior for developing hybrid lines where cross-breeding superiority is the goal, such as in poultry or maize.

(b) Processes Preventing Random Assortment of Genes

Random assortment, or independent assortment, assumes genes segregate independently during meiosis. Two primary genetic phenomena prevent this randomness.

First is Linkage. Genes located physically close to each other on the same chromosome tend to be inherited together as a unit. Because they are held together by the physical structure of the chromosome, they do not assort independently unless a crossover event occurs between them. The closer the genes, the lower the recombination frequency, resulting in non-random gametic combinations. This linkage disequilibrium ensures that specific alleles are passed to offspring in predictable blocks rather than random shuffles.

Second is Chromosomal Structural Aberrations, such as inversions or translocations. In paracentric inversions, for example, crossing over within the inverted loop leads to unbalanced gametes that are often non-viable. This effectively suppresses recombination in that region, forcing linked genes to assort together. While epistasis affects phenotypic expression ratios, it does not alter the physical segregation of alleles into gametes; thus, linkage and structural constraints are the true mechanisms preventing random assortment.

(c) Feeding Strategies for Animals in Drought Situations

Drought management in animal husbandry requires a shift from maintenance to survival and production optimization. The primary strategy is Strategic Culling, where low-productivity, infertile, or elderly animals are sold early to reduce the herd size and conserve feed resources for high-value animals.

Feed Conservation and Substitution is critical. Farmers must utilize drought-tolerant fodder crops like sorghum, pearl millet, and cowpea, which require less water. Existing green fodder should be preserved as silage or hay to bridge the dry season. Urea-Molasses Mineral Mixtures (UMMM) blocks are essential to supplement protein, allowing animals to utilize low-quality roughage more efficiently. Crop residues can be enriched by urea treatment (about 4% urea) of straw, and a limited concentrate ration, bypass-protein cakes and area-specific mineral mixture should be reserved for pregnant, lactating and young stock. Tree fodder (subabul, khejri, neem) and fodder banks carry animals through the lean period.

Water Conservation is equally vital. Strategies include installing water storage tanks, using drip irrigation for fodder, and providing water at optimal times to reduce evaporation losses. Restricted Feeding protocols may be implemented to ensure all animals receive a minimum viable ration, prioritizing lactating and growing animals. In India, integration with government schemes like the National Livestock Mission can provide subsidies for fodder seeds and water infrastructure, enhancing resilience against climate-induced feed shortages.

(d) Management of Rabbits as Meat Animals

Commercial rabbitry relies on intensive housing and accelerated breeding cycles. Animals are typically housed in wire-bottom cages or hutches to ensure hygiene and prevent coccidiosis. Breeds like New Zealand White and California are preferred for their rapid growth and high litter size.

Breeding Management is key to productivity. Does are re-mated 14 days post-kindling, leveraging their early return to estrus. With a gestation period of 30–32 days, this schedule gives a kindling interval of about 45 days, i.e. roughly 7–8 litters per doe per year in theory; under Indian farm conditions 5–6 litters is a realistic target. Litter size is often standardized to 8–10 kits to ensure uniform growth.

Nutrition involves balanced pelleted diets with about 16–18% crude protein and 12–14% crude fibre to support gut health. Health Management focuses on preventing coccidiosis (via coccidiostats in feed) and pasteurellosis (through strict biosecurity and vaccination). Environmental control is crucial; rabbits are sensitive to heat stress, so ventilation and shade are necessary to maintain feed intake. Efficient waste management and regular health checks ensure high survival rates and marketable weight, making rabbit meat a viable, low-input protein source.

(e) Factors Affecting Semen Quality In Vivo and In Vitro

Semen quality is influenced by distinct factors at the animal level (in vivo) and laboratory level (in vitro).

In Vivo Factors include Nutrition, where energy and protein deficits reduce sperm count and motility. Age affects quality, with peak fertility in young to middle-aged animals. Seasonality plays a role, as many species have seasonal breeding patterns affecting spermatogenesis. Thermal Stress is a major constraint; high ambient temperatures disrupt testicular thermoregulation, leading to reduced sperm production and increased abnormalities. Disease and hormonal imbalances also directly impair reproductive function.

In Vitro Factors relate to post-collection handling. Dilution Rate must be optimized to maintain sperm density without causing osmotic shock. The Extender Type (e.g., egg yolk-citrate or Tris-based) provides nutrients and cryoprotection. Temperature Control is critical; semen must be cooled gradually to 4–5°C to reduce metabolic activity. pH and Osmotic Pressure must be maintained to preserve membrane integrity. Microbial Contamination can lead to rapid sperm death. Finally, Cryoprotectants like glycerol are essential for freezing, protecting cells from ice crystal damage during cryopreservation.