Biology · Ch 3 — Inheritance and Variation
Deviations from Mendel's Findings
Deviations from Mendel's Findings
Mendel arrived at a few generalisations on the basis of his garden-pea experiments, such as:
i. Single trait -> single gene -> two alleles.
ii. The two alleles show an interaction in which one is completely dominant.
iii. Factors (genes) for different traits present on different chromosomes assort independently.
With the passage of time a number of deviations were observed and identified in the post-Mendelian era; they gave additional information on the patterns of inheritance and are described together as Neo-Mendelism.
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Deviations from Mendelism are:
a. Single trait -> single gene -> two alleles showing interactions like co-dominance and incomplete dominance.
b. Single trait -> single gene -> more than two alleles (multiple allelism).
c. Single trait -> more than one gene (polygenic inheritance) showing different epistatic interactions or an additive effect.
d. A single gene influencing many traits (pleiotropy).
It was observed that the phenotypic expression of a gene can be modified or influenced by another gene. These gene interactions are of two types:
i. Intragenic interactions occur between the alleles of the same gene, e.g. incomplete dominance and co-dominance; they also occur within the multiple-allele series of a gene. …