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CO 03 Extension to Mendel: complexities in relating genotype to phenotype
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1.Single-gene inheritance : a.deviation from complete dominance and recessiveness. b.Multiple alleles c.One gene determine more than one trait 2. Multifactorial inheritance Extension to Mendel
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1.Single-gene inheritance : a.deviation from complete dominance and recessiveness. b.Multiple alleles c.One gene determine more than one trait 2. Multifactorial inheritance Extension to Mendel
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Fig. 3.2 Different dominant relationship
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Fig. 3.3 Pink flower are the result of imcomplete dominance
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Fig. 3.4 In codominance, F1 hybrid display the traits of both parents spotted dotted
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1.Single-gene inheritance : a.deviation from complete dominance and recessiveness. b.Multiple alleles c.Recessive lethal allele d.One gene determine more than one trait 2. Multifactorial inheritance Extension to Mendel
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Fig. 3.5 ABO blood type are determined by three alleles of one gene
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Fig. 3.6 How to establish the dominance relations between multiple alleles
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Mutations are the source of new alleles Wild-type allele: frequency more than 1% Mutant allele: frequency less than 1% Monomorphic (One wild-type allele) ABO blood type: polymorphic agouti black/yellow black
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1.Single-gene inheritance : a.deviation from complete dominance and recessiveness. b.Multiple alleles c.Recessive lethal allele d.One gene determine more than one trait 2. Multifactorial inheritance Extension to Mendel
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Two alleles with recessive lethal Some alleles may cause lethality
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Table 3.1
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1.Single-gene inheritance : a.deviation from complete dominance and recessiveness. b.Multiple alleles c.Recessive lethal allele d.One gene determine more than one trait Extension to Mendel A single gene determines a number of distinct and seemingly unrelated characteristics is known as pleiotropy.
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Sickle-cell anemia Mutant -globin aggregates to form long-fiber Pleiotropy
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Pleiotropy of sickle-cell anemia: dominance relation vary Cells break down Oxygen drops Cells break down before malarial has a chance to reproduce
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1.Single-gene inheritance : a.deviation from complete dominance and recessiveness. b.Multiple alleles c.One gene determine more than one trait 2.Multifactorial inheritance a.Two genes can interact to determine one trait b.Heterogeneous trait c.The same genotype does not always produce the same phenotype Extension to Mendel
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1.Single-gene inheritance : a.deviation from complete dominance and recessiveness. b.Multiple alleles c.One gene determine more than one trait 2.Multifactorial inheritance a.Two genes can interact to determine one trait b.Heterogeneous trait c.The same genotype does not always produce the same phenotype Extension to Mendel
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Fig. 3.11 How two genes interact to produce novel phenotypes 9:3:3:1, four distinct phenotypes, dihybrid cross of two independent assortment genes F2 self cross
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Fig. 3.12 Complementary gene action One dominant allele of each of two genes is necessary to produce the phenotypes.
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Fig. 3.13 Epistatic: the effect of one gene hides the effect of the other gene Recessive epistasis Addition of A or B sugars H allele is epistatic to the I gene
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Fig. 3.14 Dominant epistasis A produce particular color, but B dominant allele epistatic to A
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Table 3.2 Four classes of genotypes produce a variety of phenotypic ratios
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Imcomplete dominance in interaction of two genes
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Fig. 3.15 Genetic Heterogeneity
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Heterogeneous trait A mutation at any one of a number of genes can give rise to the same phenotype
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Fig. 3.18 Pedigree analyses
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1.Single-gene inheritance : a.deviation from complete dominance and recessiveness. b.Multiple alleles c.One gene determine more than one trait 2.Multifactorial inheritance a.Two genes can interact to determine one trait b.Heterogeneous trait c.The same genotype does not always produce the same phenotype Extension to Mendel
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The same genotype does not always produce the same phenotype 1.Modifier genes 2.Environment Penetrance: occurrence in population Expressivity: seriousness in the individuals
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Modifier genes Major genes have a large influence, while modifier genes have a more subtle, secondary effect. Modifier genes alter the phenotypes produced by the allele of other genes. Example: tail length of mouse T allele: 10%, 50%, 75% of the normal tail-length
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Fig. 3.19 Permissive temp. Restrictive temp. The Environment can affect the phenotypic expression
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Even continuous variation can be explained by extensions to Mendelian analysis
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The more genes or alleles, the more possible phenotypic classes, and the greater the similarity to continuous variation
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Fig. 3a.p64
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TABLES
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Fig. 3.1
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Variations on complete dominance do not negate Mendel’s law of Segregation
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Fig. 3.8 Plant incompatibility system promote outbreeding and allele proliferation
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Fig. 3.9 Some alleles may cause lethality
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Fig. 3.17 Breeding studies help decide how a trait is inherited
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