BSC2011_SlideSet8_Unit2

BSC2011_SlideSet8_Unit2 - SLIDE SET VIII OUTLINE IV....

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SLIDE SET VIII OUTLINE IV. Extensions of (and exceptions to) Mendel’s rules A. Partial dominance 1. incomplete dominance 2. co-dominance B. More than 2 possible alleles at a locus 1. human ABO blood groups C. Pleiotropy D. Polygenic inheritance 1. epistasis 2. human skin color 3. human eye color
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UNIT II: SLIDE SET VIII I. Extensions of Mendel’s Rules (continued) E. Sex Linked Inheritance 1. Sex chromosomes 2. Systems of sex determination a. XY system b. X0 systems c. ZW systems d. Haplo-diploid systems e. Non-chromosomal sex determination 3. X-linked inheritance 4. Y-linked inheritance 5. Effects of sex on autosomal traits
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1. One allele completely dominates the other Exception: incomplete dominance Mendel’s gene system: Example: flower color in some flowers
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Fig. 14.10 Unusual pheno . ratio is a clue, 3rd phenotype is a clue**
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Incomplete Dominance: The relationship between 2 alleles where neither is dominant, and the heterozygous phenotype is intermediate between that of the 2 homozygotes.
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Co-dominance: When the phenotypes of both homozygotes appear together in the heterozygote (i.e., The heterozygote phenotype is not simply “intermediate” as with incomplete dominance) 1. One allele completely dominates the other Exception: co-dominance Note : Both incomplete dominance and codominance genetics problems work the same way. The only difference is in the way the cell cellular machinery works out the phenotypic expression.
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Co-dominance: e.g., “roan” coat color in cattle colored fur X white fur 2 co-dominant alleles for color (one for a color and one for white, and both alleles are expressed in the heterozygote)
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BB = black fur bb = white fur Bb = roan A roan cow was mated with a roan bull over several years and they produce 12 calves. How many calves would be expected to be white?
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-when there are more than 2 versions (alleles) of a single gene NOTE! A diploid organism will still have only 1 pair of alleles per gene (there are just more possible combinations of 2 alleles in heterozygotes) Example: coat color in rabbits (1 gene, 4 alleles) cc chch cchcch CC Albino Himalayan Chinchilla Brown C > Cch > Ch > c 2. Two possible alleles for each gene Exception: multiple alleles
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Antibodies Substances produced by the vertebrate immune system that recognize, bind to, and destroy foreign substances (“antigens”). Antigens The foreign substances recognized by antibodies. Example: human A,B,O blood-type determination Multiple alleles: e.g., red blood cells have surface antigens (proteins like Rh factors & polysaccharide molecules like “IA” and “IB”)
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IA > i IB > i IA = IB anti-B anti-A none anti-A, anti- B antibodies * e.g., a Type A person makes anti-B antibodies IA & IB alleles are dominant over i & co-dominant with each other.
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Human ABO blood phenotypes and genotypes: 3 alleles IA allele codes for A antigens (I=immunoglobulin) IB allele codes for B antigens i allele codes for no antigens
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BSC2011_SlideSet8_Unit2 - SLIDE SET VIII OUTLINE IV....

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