Unformatted text preview: ends on penetrance and expressivity Modifier genes produce 2 effects on phenotype Penetrance: how many members of a population with a particular genotype show the expected phenotype High penetrance = high incidence of the phenotype Low penetrance = low incidence of the phenotype Expressivity: degree to which a phenotype is expressed Modifier gene: genes having a subtle, secondary effect Siamese car coloring & egg incubation temp. in alligators Environment can affect the phenotypic expression Continuous Variation: Still Mendelian Applications Discontinuous trait: clearcut traits, easy to score Many of the traits Mendel used in pea plants Some of ones we did in class (i.e. ear lobes) Continuous traits: trait that has a wide range of values Height Skin tone Weight Often referred to as "qualtitative traits" Usually polygenic: controlled by multiple genes Mouse Coat Color & Tail Length 0 Gene 1: agouti or other color patterns Dominance series epistasis epistasis Gene 2: black or brown Gene 3: albino or pigmented Gene 4: Short, long or somewhere in between tail polygenic...
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- Fall '03