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Date Created: 04/27/14
Extending Mende39s rules Tuesolay April 15 ZD14 927 PM Chapter 145 Extending Mende39s Rules 0 Mendel worked w simple inheritance Linkage What Happens When Genes Are Located on the Same Chromosome o Linkage tendency of particular alleles of different genes to be inherited together I Happens when genes are on the same chromosome I Sex inkage is not the same as linkage in Sex inkage does not tell location of alleles relative to other genes Linked Genes Do Not Assort Independently I Linked genes transmit together gt no independent assortment The Role of Crossing Over I Many crosses of flies provided information on whether linked traits always stay linked I Most of the males carried the linked trait but a small group had novel combinations I Recombinants resulted from crossing over produced novel allele combinations I Typical crosses produce four gamete types while linkage produces two gamete types I The farther genes are apart the more likely crossing over will occur between them I Genetic map diagram showing relative position of genes along a chromosome How Many Alleles Can a Gene Have 0 Multiple allelism more than two alleles for the same gene 0 Polymorphic many phenotypes I Example Blood type quotA quotB and i alleles I Each I gene allele controls the production of a different polysaccharide attach to a glycoprotin found in plasma membrane of red blood cells I quotA and quotB code for different forms of an enzyme that adds a different sugar to the end of the polysaccharide I The i allele codes for non functiona form of the enzyme so NO sugar is added to the polysaccharide Are Alleles Always Dominant or Recessive Codominance I Both alleles are expressed at the same time in Example Cows express both black and white coat colors Incomplete Dominance I Both alleles are expressed both neither are dominant Does Each Gene Affect Just One Trait 0 Genes can influence more than one trait I Example FBN1 allele is associated with disproportional limbs abnormally shaped chest severe heart defects Is There More to Phenotype than Genotype The Environment Affects Phenotypes I Phenotypes produced are strongly affected by environment in Example temperature sunlight nutrients competition I Genebyenvironmentinteractions in Example medical treatments of genetic diseases in Phenylketonuria PKU must be placed on ow phenyaanine diets to avoid mental retardation Interactions Between Genes Affect Phenotypes I Combination of genes work to control a single trait in Example comb shape in chickens in Rose comb x Pea comb all walnut combs Biology 180 Page 1 Can Mende39s Principles Explain Traits That Don39t Fall into Distinct Categories o Discrete traits categorical I Example pea color 0 Quantitative traits continuous I Example height weight 0 Herman NilssonEhle discovered that quantitative traits fit a normal distribution 0 Polygenic inheritance multiple genes add to the expression of the phenotype Biology 180 Page 2