Inheritance160-page17

Inheritance160-page17 - Several of the pigment genes are...

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Inheritance Patterns - 17 Continuous Variation in Polygenic Inheritance When several copies of a gene interact, continuous variation within the population results. Continuous variation can most easily be demonstrated when population data shows a bell-shaped distribution pattern when graphed. Skin and hair pigmentation and height are two examples of such polygenic inheritance in humans. It is believed that there are at least 3 independent genes, each of which lacks dominance, responsible for producing the melanin pigment in human skin (and in hair). Controlling Genes - Epistasis (means standing upon or stopping) We have some gene interactions in which one gene controls or alters the expression of a second gene, so that the expected Mendelian phenotypes do not get expressed. A controlling gene is called an epistatic gene.
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Unformatted text preview: Several of the pigment genes are subject to epistasis. The gene to distribute pigment is overridden by a second gene that blocks (inhibits) pigment production. Examples: Mice can have black or brown pigmented fur depending on the inheritance of a gene for pigmentation. Black is dominant and brown, recessive. A second, independent gene prevents the distribution of any pigment in the fur. This gene, when recessive, results in white mice. In corn, expression of the pigment gene is also controlled by an epistatic gene. Epistatic genes can vary in how they control, resulting in different patterns and inheritance ratios as shown in the diagrams. In corn, distribution of pigment requires the epistatic dominant allele....
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This note was uploaded on 12/29/2011 for the course BIO 151 taught by Professor Edwards during the Spring '10 term at SUNY Stony Brook.

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