Lecture 19 - modefied mendelian genetics

Lecture 19 - modefied mendelian genetics - Lecture 19 June...

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Extensions and Modifications of Mendelian Principles 1. Phenotype and phenotypic ratio changes at single locus 2. Phenotypic ratio changes at two locus Lecture 19 June 8, 2011 Chapter 5
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Types of Dominance ± Not all traits or characteristics exhibit dominance. ¾ Complete Dominance ² heterozygous genotype exhibit one of the homozygous genotype. - One allele dominates ¾ Incomplete Dominance ² heterozygous genotype exhibit intermediate phenotype between the phenotypes of the two homozygous genotypes. - Both alleles partially dominates ¾ Codominance ² heterozygous genotype exhibit both phenotypes of the two homozygous genotypes. - Both allele dominants ± Depend on the relationship between the two alleles ¾ intro-genic or allelic interaction ¾ LQWHUDFWLRQ EHWZHHQ WKH ³SURGXFWV´ RI WKH alleles ¾ Same type of genotype (heterozygous) generate different types of phenotype
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Incomplete Dominance ± Heterozygote Pp shows violet color instead of purple or white (the parental phenotype) ± Genotypic and phenotypic F2 ratios are same ± Normally designated as P 1 or P 2 . ± Allele P encodes an enzyme involved in pigment synthesis ¾ PP produces enough pigment to make the skin darker ² purple ¾ pp produce no pigment ² white ¾ Pp produce ½ pigment ² violet - Intermediate between the two homozygous phenotypes
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Codominance ± Heterozygote simultaneously expresses the phenotypes of both alleles. ± Example: MN blood group in humans (Eskimo) ² M and N designate two forms of antigens on the surface of red blood cells. ² Alleles are designated L M and L N ² Individuals can exhibit either one or both alleles. G e notyp e Ph e notyp e L M L M M L M L N MN L N L N N
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Codominance ± A mating between two MN parents can produce children of all three blood types. ± Heterozygotes are codominant
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Lecture 19 - modefied mendelian genetics - Lecture 19 June...

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