Phenotype Variability(L3)

Phenotype - Phenotype Variability Penetrance and Expressivity By Ilona Miko Ph.D(Write Science Right 2008 Nature Education Citation Miko I(2008

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Phenotype Variability: Penetrance and Expressivity By: Ilona Miko, Ph.D. (Write Science Right) © 2008 Nature Education Citation: Miko, I. (2008) Phenotype variability: penetrance and expressivity. Nature Education 1(1) Sometimes, identical genes will produce different expression patterns. Why? Geneticists are now examining the "penetrance" and "expressivity" of genotypes and their phenotypes. Dominance relationships between alleles for a given trait can impact phenotypic ratios, but interactions between different genes can also impact phenotype. Such traits that result from the interaction among multiple genes and their environment are called complex traits. So, given a specific trait, how can we tell whether it is complex? One way to recognize a complex trait is through inconsistent inheritance patterns in successive generations. For example, a dominant trait might skip an entire generation yet be expressed in the subsequent generation. How is this possible? The answer to this question lies in the concepts of penetrance and expressivity. Penetrance Different epigenetic factors play an important role in the penetrance of cancer- assocated alleles. Copyright 2004 Jeanne Kelly (artwork). National Cancer Institute.
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When studying the relationships between genotype and phenotype, it is important to examine the statistical occurrence of phenotypes in a group of known genotypes. In other words, given a group of known genotypes for one trait, how many identical genotypes show the related phenotype? You might be surprised to learn that, for some traits, the phenotype might not occur as often as the genotype. For example, say everyone in population W carries the same allele combinations for a certain trait, yet only 85% of the population actually shows the phenotype expected from those allele combinations. The proportion of genotypes that actually show expected phenotypes is called penetrance. Thus, in the preceding example, the penetrance is 85%. This value is calculated from looking at populations whose genotypes we know. In fact, large population studies are necessary for measuring penetrance, and studies of penetrance help us predict how likely it is that a trait will be evident in those who carry the underlying alleles. In general, when we know that the genotype is present but the phenotype is not observable, the trait shows incomplete penetrance. Basically, anything that shows less than 100% penetrance is an example of incomplete
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This note was uploaded on 07/10/2011 for the course BIO 390 taught by Professor Dr during the Spring '11 term at McMaster University.

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Phenotype - Phenotype Variability Penetrance and Expressivity By Ilona Miko Ph.D(Write Science Right 2008 Nature Education Citation Miko I(2008

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