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CO 03 Extension to Mendel: complexities in relating genotype to phenotype.

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Presentation on theme: "CO 03 Extension to Mendel: complexities in relating genotype to phenotype."— Presentation transcript:

1 CO 03 Extension to Mendel: complexities in relating genotype to phenotype

2 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

3 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

4 Fig. 3.2 Different dominant relationship

5 Fig. 3.3 Pink flower are the result of imcomplete dominance

6 Fig. 3.4 In codominance, F1 hybrid display the traits of both parents spotted dotted

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8 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

9 Fig. 3.5 ABO blood type are determined by three alleles of one gene

10 Fig. 3.6 How to establish the dominance relations between multiple alleles

11 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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13 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

14 Two alleles with recessive lethal Some alleles may cause lethality

15 Table 3.1

16 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.

17 Sickle-cell anemia Mutant  -globin aggregates to form long-fiber Pleiotropy

18 Pleiotropy of sickle-cell anemia: dominance relation vary Cells break down Oxygen drops Cells break down before malarial has a chance to reproduce

19 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

20 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

21 Fig 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

22 Fig Complementary gene action One dominant allele of each of two genes is necessary to produce the phenotypes.

23 Fig 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

24 Fig Dominant epistasis A produce particular color, but B dominant allele epistatic to A

25 Table 3.2 Four classes of genotypes produce a variety of phenotypic ratios

26 Imcomplete dominance in interaction of two genes

27 Fig Genetic Heterogeneity

28 Heterogeneous trait A mutation at any one of a number of genes can give rise to the same phenotype

29 Fig Pedigree analyses

30 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

31 The same genotype does not always produce the same phenotype 1.Modifier genes 2.Environment Penetrance: occurrence in population Expressivity: seriousness in the individuals

32 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

33 Fig Permissive temp. Restrictive temp. The Environment can affect the phenotypic expression

34 Even continuous variation can be explained by extensions to Mendelian analysis

35 The more genes or alleles, the more possible phenotypic classes, and the greater the similarity to continuous variation

36 Fig. 3a.p64

37 TABLES

38 Fig. 3.1

39 Variations on complete dominance do not negate Mendel’s law of Segregation

40 Fig. 3.8 Plant incompatibility system promote outbreeding and allele proliferation

41 Fig. 3.9 Some alleles may cause lethality

42 Fig Breeding studies help decide how a trait is inherited


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