Question

The inheritance rule was initially discovered by Mendel and it depends on clear or qualitative traits. The theory was based on a single gene that was responsible for one character. However, expression of many traits are not governed by a single gene, rather can involve multiple genes as well as additive effects. This kind of inheritance pattern is known as quantitative (See cogbooks -> Genetic analysis of populations for more information) and is demonstrated by East (1916) as well as others. He performed experiments using 2 homozygous, pure-breeding lines of Nicotiana longiflorathat differed in corolla length. After crossing these lines, F1 offspring had an intermediate length for corolla and had same variation level as in parents. But found a very different result for F2 and F3 than expected. Discuss the reasons for this result and if it agrees/disagrees with Mendel’s law. Using obtained knowledge so far, what kind of cumulative effects would you add to this variation?

Here is a paper by East (1916):

https://myasucourses.asu.edu/bbcswebdav/pid-1611343-dt-forum-rid-124933901_1/courses/2018SummerA-X-BIO340-46443-44912/East_1916.pdf

Answer 1

Edward East (1916) crossed pure breeding (inbred) lines of tobacco (Nicotiana longiflora) that differ from each other for the corolla height. The F1 plants had intermediate corolla height. The F2 plants were also intermediate but were more variable. He selectively bred the plant with the smallest and largest corolla height from F2, F3, and F4 individuals.
He obtained plants with a small and tall corolla like that of the original parent plants. This was due to the fact that the corolla height in this plant is regulated by more than one genetic loci. It is a polygenic trait and the total number of the dominant allele from each gene together impart the phenotype. The phenotypes do not exist in distinct categories but exhibit a continuous variation. Also, corolla height in this plant is affected by some environmental factors.