Pedigree analysis is therefore required to track the

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Unformatted text preview: e of environment, modifier genes and chance penetrance – percentage of the population with a particular genotype, that demonstrate the expected trait expressivity – the degree or intensity with which a particular genotype is expressed in a phenotype within a population 62 Identical genotypes Complete penetrance Incomplete penetrance 63 Identical genotypes Constant expression Variable expression ie. beagles. - amount of white - they all show white which is complete penetrance, variable expression is the amount of white 64 Identical genotypes Incomplete penetrance and variable expression 65 e.g., retinoblastoma - cancer of the retina - dominant allele - not all persons carrying the allele get disease - 75% penetrance (25% do not develop the disease) - of those who do get the disease, some get in it only one eye - 30% expressivity 66 Sex-linked traits and related oddities Chapter 5 pp 98-100 67 genes can also determine differences between sexes Sex-linked traits - due to genes ON the X or Y chromosome e.g., hemophilia and color blindness humans - only X! Sex-limited traits - affect a structure or process that is found in one sex but not the other e.g., bright plumage in male birds, milk production, horns/antlers Sex-influenced traits - show up in both sexes but their expression may differ between the two sexes e.g., patterned baldness 68 007 = b_ vs b+b+(hair) -premature loss of hair from top of head, but not sides -begins in late 20s in heterozygous men, but heterozygous women show no effect -in homozygous men and women, baldness results in both, but much earlier in men -influenced by sex hormones -dominant in men, recessive in women 69 Environment Factors such as temperature, light, and altitude can affect the phenotypic expression of a genotype 70 The environment can affect the phenotypic expression of a genotype Himalyan coat pattern in cats, rabbits Enzyme non-functional Enzyme functional cooler temp causes darker fur 71 Conditional lethality – occurs with a particular type of allele which is lethal under only certain conditions permissive vs. restrictive conditions 72 Malignant hyperthermia -genetic disease triggered by certain anesthetics (halothane but not nitrous oxide) -results in uncontrolled muscle contractions, high fever -death if not treated 73 Chance Occurrences in the lives of individuals can influence the expression of some alleles. e.g., exposure to carcinogens, radiation 74 Next topic Pedigree analysis pp 53-56 Chapter 3 (tutorial 3) Chapter 5 pp 98-100 75...
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This document was uploaded on 02/25/2014.

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