Question

Edward East was a plant geneticist who was greatly interested in quantitative traits. He is also known for the Mendelian model of quantitative traits. Explain how his model works if a trait resulted from 6 genetic loci. Draw graphs in your explanation

Answer 1

East’s analysis of corolla length in Nicotiana longiflora was a capstone study integrating Mendelian genetics with a continuously varying phenotype. Gregor Mendel and Francis Galton produced profound insights into heredity by employing mathematics novel to biology. Both used Pisum sativum to illustrate different patterns of inheritance. Mendel established his ratios by studying qualitative variants. Those discrete differences were determined by individual genes, and generally displayed dominance and independent assortment, features atypical of the natural variation that attracted students of hybridization, breeding, and evolution. Mendel’s fundamental discoveries were ignored for decades, at least in part because of their questionable relevance to common phenotypic differences. In contrast, Galton studied the distribution and inheritance of continuous variation using characters such as seed-pod length in P. sativum, and human height.

Galton showed that phenotypic variation could often be approximated by Gaussian distributions. Comparing the average phenotypes of offspring with their parents , Galton discovered “regression toward mediocrity,” namely that offspring are generally less “exceptional” than their parents (i.e., they tend to deviate less from their population means). Mendel struggled to convince himself, and his contemporaries, that he had uncovered general principles, failing miserably with his second, and final, publication on interspecific Hieracium “hybrids” . In contrast, Galton observed normal distributions and “regression towards mediocrity” everywhere.

When Mendel’s principles were rediscovered in 1900, two central problems needed to be resolved: determining the generality of Mendelian inheritance, and understanding its connection to continuous variation. Famously, Morgan began his Drosophila experiments skeptical of Mendelism’s generality. One of the great triumphs of early 20th century genetics was reconciling Mendelian genetics with Galton’s “biometrical” observations.