Chapter 6: Introduction to Genetics

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Chapter 6Introduction to Genetics

• Section 6-4
• Different Types of Inheritance

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Incomplete Dominance

• Occurs when the heterozygous phenotype is in
  between both homozygous phenotypes
• Example Snapdragons (Red is dominant)
• RR red flowers rr white flowers
• Rr pink flowers

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Sometimes 2 different letters are used to show
incomplete dominance
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Codominance

• Occurs when both alleles are equally expressed in
  the heterozygous phenotype
• Ex. Erminette chickens
• BB black feathers bb white feahters
• Bb black and white checkered feathers
• (some feathers black, some feathers white)

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Roan Cows show CODOMINANCE
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Multiple Alleles

• Occurs when there are more than two alleles for a
  gene
• Example Human blood groups
• Type A, Type B, Type AB, Type O
• Three alleles IA, IB, i

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Polygenic Traits

• Traits controlled by more than one gene
• Many human traits such as body shape, facial
  appearance, mouth and eye position, height, and
  skin color are polygenic
• Also.feather color in parakeets

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Polygenic Traits
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Sam