Avian Physiology

• Major Genes for Tropical Heat Tolerance in Poultry:

• Naked Neck Gene ($Na$): Reduces feather coverage by $30\%\text{ to }40\%$, improving convective heat loss from neck and body.
• Frizzle Gene ($F$): Curls feathers outwards away from the body, facilitating heat dissipation.
• Dwarf Gene ($dw$): Sex-linked dwarfism reducing metabolic heat production.
  • Fibromelanosis ($Fm$): Causes hyperpigmentation of dermal, connective, and visceral tissues (black meat/bones, e.g., in Kadaknath and Silkie chicken), but is not a heat tolerance gene.

• Frizzle Gene Genetics in Domestic Fowl:
• The frizzle feather trait is governed by an autosomal, incompletely dominant gene ($F$).
• Genotypes:
• Heterozygotes ($Ff$): Desirable curled, frizzled plumage; provides enhanced heat tolerance without extreme fragility.
• Homozygotes ($FF$): Extreme "woolly" brittle feathers that break off easily, leading to almost complete bareness.

Correct option: (2) Incompletely dominant