Genetic Maternal Effect on Phenotype

                As I have informed about the inheritance of maternal mitochondria, I remembered another sexual influence on phenotype, the genetic maternal effect on some treats. However, it is important to clarify that cytoplasmic inheritance is different from genetic maternal effect. In mithocondrial inheritance, the genes for the characteristic are inherited from only the mother. In genetic maternal effect, the genes are inherited from both parents, but the offspring’s treat is determined not by its own genotype but by its mother’s genotype. The maternal effect usually arises when substances in the egg’s cytoplasm, which are encoded by the mother’s nuclear genes, influence the offspring’s phenotype in its early development (Pierce, 2008). According to William et al., these substances are gene products of regulation, which active or repress the expression of the zygote genome.

Genetic maternal effect in shell coiling of Limnaea peregra (Pierce, 2008)

                The best didactic example of maternal effect on phenotype is seen on the species Limnaea pelegra. The shell of its snails usually coils to the right (dextral coiling) but some snails are left-coiling shell (sinistral coiling). The allele for dextral (s+) is dominant over the allele for sinistral (s). The direction of the coiling is influenced by the way in which the cytoplasm divides soon after the fertilization. This event is determined by a substance produced by the mother and passed to the offspring through the egg’s cytoplasm (Pierce, 2008). As the progeny’s phenotype is determined by the mother’s genotype, not her phenotype, the phenotype of the mother is not necessarily the same as the offspring.

                As you can see on the picture, dextral males s+s+ crossed with sinistral females ss produce a heterozygous offspring (s+s) that have all sinistral shell, as its mother’s genotype encodes sinistral coiling. As result of the F1 self-fertilized, the genotype of F2 is 1s+s+:2s+s:1ss, all with dextral coiling (as F1 genotype produces dextral phenotype). Males can influence phenotypes here just by contributing to the genotype of their daughters, affecting the phenotypes of the daughters’ offspring (Pierce, 2008).

REFERENCES:

Klug W. S.; Cummings M. R.; Spencer C.; Palladino M. A.(2009). Concepts of Genetics. (Ninth edition) Benjamin Cummings, San Francisco. p 489.

Pierce B. A. (2008). Genetic Maternal Effect. In: Genetics: A Conceptual Approach. (third edition) W. H. Freeman and Company, New York. p 119-120.