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INCOMPLETE DOMINANCE AND CODOMINANCE

INCOMPLETE DOMINANCE AND CODOMINANCE. Neither allele has “ complete ” dominance over the other; heterozygous phenotype is a blend of the 2 homozygous phenotypes Ex: snapdragons R = red W = white RW = pink. INCOMPLETE DOMINANCE. W. W. R. R. Cross a red (RR) snapdragon with a

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INCOMPLETE DOMINANCE AND CODOMINANCE

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  1. INCOMPLETE DOMINANCEANDCODOMINANCE

  2. Neither allele has “complete” dominance over the other; heterozygous phenotype is a blendof the 2 homozygous phenotypes Ex: snapdragons R = red W = white RW = pink INCOMPLETE DOMINANCE

  3. W W R R Cross a red (RR) snapdragon with a White (WW) snapdragon. Give the genotypic and phenotypic ratios. Key: R = red flower W = white flower Cross: RRx WW Incomplete Dominance Genotypic Ratio: Phenotypic Ratio: Answer on next slide…

  4. W R RW RW R RW RW INCOMPLETE DOMINANCE Key: R = red W = white Cross: RRx WW W Genotypic Ratio: 0RR: 4RW: 0WW Phenotypic Ratio: 0 Red: 4 Pink: 0 White

  5. INCOMPLETE DOMINANCE Practice: Cross a pink snapdragon with a red snapdragon. Give the expected phenotypic and genotypic ratios. Key: __________________ Cross: _________________ Genotypic Ratio: ________________________ Phenotypic Ratio: ________________________

  6. INCOMPLETE DOMINANCE Practice: Cross a pink snapdragon with a red snapdragon. Give the expected phenotypic and genotypic ratios. R R Key: R = red W = white RW = pink Cross: _RW x RR__ Genotypic Ratio: __2RR: 2RW: 0WW__ Phenotypic Ratio: __2 red: 2 pink: 0 white_ R RR RR W RW RW

  7. Codominance – Both alleles share dominance and are always expressed if present. Ex: In chickens B = black feathers W = white feathers BW = black AND white feathers CODOMINANCE

  8. W W B B Cross a black (B) chicken with a white (W) chicken. Give the genotypic and phenotypic ratios. Key: B = black feathers W = white feathers Cross: BBx WW CODominance Genotypic Ratio: Phenotypic Ratio: Answer on next slide…

  9. W B BW BW B BW BW CODominance Key: B = black W = white Cross: BB x WW W Genotypic Ratio: 0BB: 4BW: 0WW Phenotypic Ratio: 0 black: 4 black and white: 0 white

  10. CODominance Practice: Cross two black and white feathered chickens. Give the expected phenotypic and genotypic ratios of the offspring. Key: __________________ Cross: _________________ Genotypic Ratio: ________________________ Phenotypic Ratio: ________________________

  11. CODominance Practice: Cross two black and white feathered chickens. Give the expected phenotypic and genotypic ratios of the offspring. B W Key: B = black W = white BW = black and white Cross: _BW x BW__ Genotypic Ratio: __1BB: 2BW: 1WW_ Phenotypic Ratio: _1 black: 2 black and white: 1 white_ B BB BW W BW WW

  12. Alleles for differenttraits are distributed to sex cells (& offspring) independently of one another. This law can be illustrated using dihybrid crosses. Law of Independent Assortment

  13. Tracks the inheritance of two traits. Ex. Seed shape and seed color Each pair of alleles segregates independently during gamete formation DIHYBRID CROSS

  14. Traits: Seed shape & Seed color Alleles: R round r wrinkled Y yellow y green DIHYBRID CROSS RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations

  15. RY Ry rY ry RY Ry rY ry Dihybrid Cross Gametes are placed in the punnett square

  16. RY Ry rY ry RY Ry rY ry Dihybrid Cross Put R’s back together and Y’s back together RRYY Continue filling in the Punnett Square….

  17. RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy Dihybrid Cross Genotypic Ratio: 1 RRYY: 2 RRYy: 2 RrYY: 1 RRyy: 4 RrYy: 2 Rryy: 2 rrYy: 1 rrYY 1 rryy

  18. RY Ry rY ry Phenotypic Ratio: Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy DIHYBRID CROSS

  19. If a pea plant with genotype RRYy (round, yellow peas) is crossed with a pea plant with genotype rrYy (wrinkled, yellow peas), what would the results be? Key: Cross: Gametes: Genotype: Phenotype: DIHYBRID PRACTICE

  20. OTHER PATTERNS OF INHERITANCE

  21. “Many genes” ; Many traits are controlled by more than one gene; have a variety of choices for expression. Ex: _hair color, eye color, skin tone___ Polygenic Traits

  22. Genes that have more than 2 alleles Ex: blood group. There are 3 possible alleles for this gene. Multiple Alleles

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