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Variations in Heredity

Variations in Heredity. Incomplete and C odominance. More Dragon Genetics…. A pure breeding red snapdragon is bred with a pure-breeding white snapdragon. What should we expect in the F 1 generation? X = What happened here?. All Pink?! Huh?. Incomplete Dominance.

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Variations in Heredity

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  1. Variations in Heredity Incomplete and Codominance

  2. More Dragon Genetics… • A pure breeding red snapdragon is bred with a pure-breeding white snapdragon. What should we expect in the F1 generation? X = • What happened here? All Pink?! Huh?

  3. Incomplete Dominance • Neither colour can mask the other; so the offspring express a blend of parents’ traits. • How do we represent these alleles? • Choose a letter for the gene (colour) • Choose 2 different letters to represent each allele, both will be capitals • CR and CW

  4. Try This Red snapdragon X White snapdragon • Construct a Punnett square to determine genotype and phenotype ratios in: a) F1 generation b) F2 generation

  5. Codominance • Another type of interaction, called codominance, can occur when both of the parental alleles are expressed in the offspring at the same time. (*each trait is expressed independently; no blending)

  6. Example of Codominance Red Bull (HrHr) X White Cow (HwHw) = Roan Cow (HrHw) Roan cattle have a both red and white hairs (no pink hairs)

  7. Try This Red Bull X White Cow • Construct a Punnett square to determine genotype and phenotype ratios in: a) F1 generation b) F2 generation

  8. Codominance in Humans • Human blood type is a dominant and codominant trait. • There are 3 different blood type alleles: A, B, and O. • These alleles produce 4 possible blood types: A, B, AB, and O • The various blood types specify which proteins are present on the surface of red blood cells.

  9. O is recessive to A and B • A and B are codominant • Alleles are represented as follows: • A = IA • B = IB • O = i • Determine the possible genotypes for people with each of the 4 blood types.

  10. Rhesus Factor • The Rhesus factor is a Mendelian trait and indicated by + or – after the blood type. • In reality there are 8 possible blood types: AB +/- A +/- B+/- O +/-

  11. Monohybrid Cross Worksheet • 1. All red, all heterozygous • 2. Both are heterozygous. Alleles are B (black) and b (white) • 3. a) Alleles freckles: F no freckles: fb) no freckles ffc) freckles Ff or FF • 4. a) White recessive, black dominant b) parents: Bb x Bb Offspring: BB, Bb, bb • 5. a) RRb) Rr • 6. genotypes: ½ Dd, ½ dd phenotypes: ½ purple, ½ white • 7. Ss xss • 8. F1 – yes, all heterozygous and all show dominant trait F2 – Yes, approximate 3:1 ratio (25% TT, 50% Tt, 25% tt) • 9. Not possible to determine genotypes; could be: Bb x Bb or Bb x bb (can’t be BB x Bb or BB x bb)

  12. Blood Type: Mini Case Studies • Case 1 – Grace is adopted • Case 2 – yes, he could be the father, only if mother’s genotype is Iai • Case 3 – Possible blood types: A, B, AB, O, all have equal probability (25%) • Case 4 – A (25%), AB (50%), B (25%), O (0%) • Case 5 – Could receive blood from Rhonda and Howard (Patient has antibodies to blood from Richard or Shelly) • Case 6 – Sarah: IAi George: IBiGregor: IAi Barbara: ii Rosalind: IA IB

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