Incomplete Dominance

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Incomplete Dominance Codominance
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Review of Mendels Principles

• Genes are passed parents ? offspring get one
  allele from each parent
• During Meiosis, the alleles for a gene segregate
  from each other.
• During Meiosis, genes independently assort with
  each other.

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Exceptions to Mendels principles

• Sometimes, there is no dominant or recessive
  gene, or the trait is controlled by many alleles
  or genes.

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Incomplete Dominance

• In Incomplete Dominance, every genotype has its
  own phenotype. (One allele not completely
  dominant over the other.) Third phenotype that is
  a blending of the parental traits. (2 alleles
  produce 3 phenotypes.)
• Result Heterozygous phenotype somewhere in
  between homozygous phenotype.

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1. Incomplete Dominance

• Examples
• Trait Flower Color
• Expressions Red x White ? Pink
• RR Red RW pink WW white
• straight hair, wavy, curly

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Incomplete Dominance
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Codominance

• In codominance, neither allele are dominant both
  are expressed. A cross between organisms with two
  different phenotypes produces offspring with has
  both phenotypes of the parental traits shown. 

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2. Codominance

• Both alleles contribute to the phenotype.
• Example In come chickens
• Black Chicken x White ? Speckled Chicken

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YOU tell me which type of dominance
Codominance!
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Type of Dominance?
Incomplete Dominance!
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Type of Dominance?
Incomplete Dominance!
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Test Cross (Back Cross)

• Used to determine whether an individual is
  homozygous dominant or heterozygous.
• RULES
• Always cross unknown genotype with a homozygous
  recessive.
• Observe (count) large numbers of offspring to
  insure accuracy in determining the unknown
  genotype.
• Then
• if ANY offspring show the recessive trait, the
  unknown genotype is heterozygous
• if ALL the offspring have the dominant trait, the
  unknown genotype is homozygous dominant