MBG 2040 Lecture Notes - Lecture 4: Neurodegeneration, Piebaldism, Statistical Dispersion
26 Sep 2018
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Penetrance and expressivity: penetrance, the proportion of individual organisms having a particular genotype that express the expected phenotype - variation in the population, example: incomplete penetrance, polydactyly (extra fingers and toes) is not fully penetrant. It causes loss of muscle coordination, cognitive decline and dementia. What causes incomplete penetrance and expressivity: incomplete penetrance and variable expressivity are due to the effects of other genes and to environmental factors that can alter or completely suppress the effect of a particular gene. Environmental factors that can affect phenotypic expression: 1. Chemicals: the range of phenotypes expressed by a single genotype under different environmental conditions is referred to as the norm of reaction. Mendel"s low of independent assortment: the inheritance pattern of one trait will not affect the inheritance pattern of another trait. Genetic interaction: different combinations of alleles from two or more genes can result in different phenotypes, because of interactions between their products at the cellular or biochemical level.
