Textile Sector – Cotton, Jute, Wool, Silk, Handloom, etc.

Genetics of Silk Moth Domestication


From UPSC perspective, the following things are important :

Prelims level : Read the attached story

Mains level : NA


Central Idea

  • Silk, often hailed as the queen of fibers, boasts a rich and diverse history, with roots stretching back over 5,000 years to ancient China.
  • Its story encompasses the transition from the wild silk moth (Bombyx mandarina) to the domesticated silk moth (Bombyx mori), offering a fascinating glimpse into human ingenuity and nature’s adaptability.

Silk Moth Domestication

  • Ancient Beginnings: Humans began domesticating silk moths from the wild Bombyx mandarina in China, marking the dawn of sericulture.
  • Global Reach: The domesticated Bombyx mori moth, significantly larger than its wild ancestor, now thrives worldwide, including in India.
  • Silk Powerhouse: India’s prowess in silk production makes it the second-largest raw silk producer globally, after China.

Silkworms and Mulberry Leaves

  • Exclusive Diet: Caterpillars, known as silkworms, feed solely on the leaves of mulberry plants (genus Morus).
  • Cocoon Construction: The domesticated silk moth extrudes silk fibers of remarkable length, up to 900 meters, to construct larger cocoons. These caterpillars have lost the ability to fly and their pigmentation, adapting to human care.

Diversity in Silk

  • Wild Silk Varieties: “Wild” silks, including muga, tasar, and eri, are derived from various moth species such as Antheraea assama, Antheraea mylitta, and Samia cynthia ricini.
  • Contrasting Characteristics: Non-mulberry silks differ significantly from mulberry silks, featuring shorter, coarser, and harder threads.

The Enigmatic Cocoon Colors

  • Natural Variations: Domesticated silk moth cocoons come in a stunning array of colors, including yellow-red, gold, flesh, pink, pale green, deep green, and white.
  • Human Influence: Selective breeding for differently colored cocoons aimed to create colored silks, but these pigments are water-soluble, eventually fading. Acid dyes are used to achieve colored silks in the market.
  • Origins of Pigments: Pigments in cocoons are derived from carotenoids and flavonoids produced by mulberry leaves. Silkworms ingest these chemicals, which are then bound to silk proteins and spun into a single fiber.

Mutant Strains and Genetic Insights

  • Valuable Resource: Mutant strains of silk moths have emerged due to mutations in genes governing pigment uptake, transport, and modification.
  • Diversity from Domestication: Silk domestication’s molecular basis has been primarily explored in China and Japan, with notable contributions from Indian scientists.

Decoding Cocoon Colors: A Model Emerges

  • Genetic Factors: Researchers at Southwest University in Chongqing, China, proposed a model explaining how different mutations create diverse cocoon colors.
  • Key Genes: Genes like Y, C, F, Rc, and Pk play roles in pigment transportation and absorption, leading to variations in cocoon colors.
  • Green Cocoon Mystery: Mutations in the Y gene result in green cocoons when carotenoids are not absorbed, but flavonoids are. The intensity of green depends on other genes’ mutations, affecting flavonoid uptake.
  • Flavonoid Cluster: A cluster of closely related genes influences flavonoid uptake in cocoons.

Gene Manipulation and Domestication

  • Hybrid Offspring: Researchers have created hybrid moths by interbreeding domesticated and ancestral silk moths.
  • Apontic-like Gene: Mutations in the apontic-like gene revealed differences in melanin production between domesticated and wild silk moths.
  • Regulatory Sequences: Variations in gene regulation sequences dictate when and where genes are activated or deactivated.

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