Maternal Effects: Shell Coiling in Limnaea and Pigmentation in Ephestia

Maternal effects refer to non-genetic influences of the mother on the phenotype of her offspring. These effects are mediated through factors like maternal cytoplasmic components, gene products, or the environment. Two classic examples of maternal effects are shell coiling in Limnaea (a freshwater snail) and pigmentation in Ephestia (flour moth).

1. Shell Coiling in Limnaea

• Phenomenon:

  1. The direction of shell coiling in Limnaea stagnalis (dextral or sinistral) is determined by maternal genotype.
  2. Dextral (right-handed) coiling is more common than sinistral (left-handed) coiling.

• Genetic Basis:

  • Controlled by a single gene with two alleles:
    • Dominant allele (D) leads to dextral coiling.
    • Recessive allele (d) leads to sinistral coiling.
  • The offspring’s phenotype reflects the genotype of the mother, not their own genotype.

• Mechanism:

  • During early cleavage stages of the zygote, the maternal gene products (mRNA and proteins) influence the orientation of cell division, determining the coiling pattern.

• Significance:

  1. Demonstrates cytoplasmic influence over nuclear genes.
  2. Highlights how early developmental processes shape organismal traits.

2. Pigmentation in Ephestia

• Phenomenon:

  1. In Ephestia kuehniella (flour moth), eye color pigmentation is influenced by the maternal genotype.
  2. Wild-type eye color (brown) and mutant (red) pigmentation depend on maternal gene products.

• Genetic Basis:

  • Controlled by a single gene where:
    • Dominant allele (B) leads to brown eyes.
    • Recessive allele (b) leads to red eyes.
  • Pigmentation in the offspring reflects the genotype of the mother due to maternal transfer of gene products during oogenesis.

• Mechanism:

  • Maternal enzymes involved in pigment biosynthesis are deposited in the egg cytoplasm, determining eye color before the offspring's genotype can take effect.

• Significance:

  1. Highlights the influence of maternal contributions on phenotypic traits.
  2. Serves as a model for understanding cytoplasmic inheritance and maternal influence in development.

Conclusion

Maternal effects in shell coiling in Limnaea and pigmentation in Ephestia exemplify how maternal genotype and cytoplasmic contributions influence offspring traits. These phenomena demonstrate the importance of maternal contributions in shaping phenotypes, enriching our understanding of heredity and development.