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Bio - Lecture 11

Bio - Lecture 11 - -An example in the gene(I encoding for...

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Sheet1 Page 1 Lecture 11: Inheritance **Learn first theory of Genetics Mendels Theory of independant assortment -THe theory of INdependant Assortment: ->States that genes will assort independently and will not affect the expression of another (if they are not linked) Mendel observed this by performing dihybrid crossings Instead of crossing peas varying in only one trait (monohybrid), he crossed peas differing in two traits: -Shape: Round (R) or wrinkled (r) -Color: Yellow (Y) or green (y) In a dihybrid cross, if the P generation is pure-breeding, all of the F1 generation will be heterozygous for both traits Mendel predicted the F2 generation would have a ratio of 9:3:3:1 if the alleles assorted independently of eachother: 9 - Round and yellow 3 - Round and green 3 - Wrinkled and yellow 1 - Wrinkled and green -Mendel found this to be the case Codominance: -Sometimes alleles can both be dominant and not affect the expression of its homologous gene ->The phenotype of the offspring displays both traits
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Unformatted text preview: -An example in the gene (I) encoding for the blood type->It (I) has three alleles: A, B, and O (i)->Ia adds agalactosamine, Ib adds galactose, and i does not add any sugar to the surface of RBC-THese determine the ABO blood group Incomplete Dominance:-Not all alleles are completely dominant or recessive-Sometimes they exhibit incomplete dominance-In this effect, the phenotype of the F1 generations will show a blend of the traits of the P generation-Blending of the trais is seen if the alleles are incompletely dominant Epistasis:-Sometiemes genes affect eachother which may result in their expression-This is called Epistasis-An example occurs with the purple pigment in corn-When two or more genes will work together to have an effect on one phenotype Pleiotropic effects and continuous variation-Pleiotropic alleles are those that affect more than one trait-Continuous variation occurs since serveral genes may determine one phenotype and those genes segregate randomly...
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