POST MENDELIAN GENETICS

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POST MENDELIAN GENETICS
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EXTENSION OF MENDELS RULES

• Phenotypic variation is not always due to simple
  dominance/recessive-ness of genes

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EXTENSION OF MENDELS RULES

• Some Traits Deviate from Mendelian Patterns
• Incomplete Dominance
• Co Dominance
• Environmental Effects
• Quantitative Traits

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INCOMPLETE DOMINANCE

• No Allele Is Completely Dominant

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Incomplete dominance in Snapdragon flower color
Parental generation
X
RR
rr
F1 generation All Heterozygotes
Rr
Self-fertilization
F2 generation
1/4 RR
1/4 Rr
1/4 Rr
1/4 rr
Red
Pink
White
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INCOMPLETE DOMINANCE

• Red allele red pigment
• White allele no pigment
• In heterozygous form

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CODOMINANCE

• Two alleles specify different phenotypes, but

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CODOMINANCE

• Blood type
• Determined by type of carbohydrate on RBC
  membrane
• 3 possible alleles

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CODOMINANCE

• Blood Type
• With alleles AA or AO, you have
• With alleles BB or BO, you have
• With alleles OO, you have
• With alleles AB, you have

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CODOMINANCE

• ABO Blood System

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CODOMINANCE

• Our immune system produced proteins
  (antibodies) that recognize foreign
  carbohydrates and causes foreign cells to clump
  together
• A Blood has
• B Blood has
• O Blood has

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ENVIRONMENTAL EFFECTS

• Environmental conditions help
• determine expression of genotype
• Ex

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ENVIRONMENTAL EFFECTS

• Temp. sensitive enzyme acts at surface of body

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QUANTITIVE TRAITS
A result of more than one gene contributing to
phenotype
Polygenetic Inheritance