Mendelian Patterns of Inheritance

The norm of reaction is the phenotype range that individuals with a particular genotype exhibit under differing environmental conditions.
Gene interaction – a single character is controlled by two or more gene, which has two or more alleles.
In some gene interactions, the alleles of one gene mask the expression of the alleles of another gene. This phenomenon is called epistasis.
We have discussed the inheritance of characters with clearly defined phenotypic variants, such as red or white eyes in fruit flies and round or wrinkle seeds in garden peas. These are known as discrete traits, because the phenotypes do not overlap. Traits that show continuous variation over a range of phenotypes are called quantitative traits. Quantitative traits are usually polygenic, which means that multiple genes contribute to the outcome of the trait. Also, environmental factors often have a major effect on quantitative traits.
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