Bellwork: Thurs. Jan. 18, 2018 Dihybrid: 2-Factor Cross: First Generation: F1   Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy): Cross: RRYY x rryy (R) = Round seeds (r) = wrinkled seeds (Y) = Yellow seeds (y) = green seeds Genotypic Ratio: ______________ Phenotypic Ratio: ______________

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Incomplete & Codominance

Incomplete Dominance: when one allele is not completely dominant over another. The heterozygous phenotype is a “mix of the two homozygous phenotypes. A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW).

Incomplete dominance – when one allele is not completely dominant over the other allele WW = White RR = Red WW X RR RW = Pink Genotypic Ratio:__________ Phenotypic Ratio:_________

What happens if you cross the offspring (F1) generation? RW x RW Genotypic ratio Phenotypic Ratio Phenotypic Ratio: Genotyopic Ratio:

Codominance Is a lot like incomplete dominance - A hybrid organism shows a third phenotype --- not the usual dominant versus recessive traits. BUT in codominance both traits show up AT THE SAME TIME!!

Co-dominance: when both alleles contribute to the phenotype. A cross of black chicken (BB) with a white chicken (WW) produces all speckled offspring (BW). BB = black feathers BW = black and white feathers WW = white feathers Genotypic Ratio: Phenotypic Ratio:

Or…. Roan coat color in horses and cows.

Co-dominance: Roan fur. Cattle can be red (RR = all red hairs), white (rr = all white hairs), or roan (Rr = red & white hairs together).  Notice how this cross looks just like the others we have done earlier with dominant and recessive alleles – I would have to tell you this is a co-dominant cross!!!. Cross: ______ X _______ Genotypic Ratio:_____________ Phenotypic Ratio:____________

Now let’s cross two roans: Cross:_____ X______ Genotypic Ratio: Phenotypic Ratio:

roan horses

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The Punnett square predicts a Genotypic Ratio: 1:1:2:2:4:2:2:1:1 Phenotypic Ratio: 9:3:3:1 When Mendel crossed plants that were heterozygous dominant for round yellow peas, he found that the alleles segregated independently to produce the F2 generation. F2 Represents: Independent Assortment

Bellwork: Mon???. Jan. 20??, 201? Dihybrid: 2-Factor Cross: First Generation: F1   Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy): Cross: RRYY x rryy (R) = Round seeds (r) = wrinkled seeds (Y) = Yellow seeds (y) = green seeds Genotypic Ratio: ______________ Phenotypic Ratio: ______________

Bellwork: Mon. Jan. 9, 2012 RRYY x rryy Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy): Set up the Punnet Square for this cross: RRYY x rryy