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Incomplete Dominance and Codominance

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Presentation on theme: "Incomplete Dominance and Codominance"— Presentation transcript:

1 Incomplete Dominance and Codominance
Mendelian Genetics 1/1/2019 Incomplete Dominance and Codominance

2 Mendelian Genetics 1/1/2019 Incomplete Dominance Neither allele has “complete” dominance over the other; heterozygous phenotype is a blend of the 2 homozygous phenotypes Ex: snapdragons RR = red rr = white Rr = pink

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

4 Incomplete Dominance Genotypic Ratio: 0RR: 4Rr: 0rr Phenotypic Ratio:
Mendelian Genetics 1/1/2019 Incomplete Dominance Key: RR = red rr = white Cross: RR x rr R r r Genotypic Ratio: 0RR: 4Rr: 0rr Phenotypic Ratio: 0 Red: 4 Pink: 0 White Rr

5 Mendelian Genetics 1/1/2019 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 R R R RR RR r Rr Rr
Mendelian Genetics 1/1/2019 Incomplete Dominance Practice: Cross a pink snapdragon with a red snapdragon. Give the expected phenotypic and genotypic ratios. R R Key: RR = red rr = white Rr = pink Cross: _Rr x RR__ Genotypic Ratio: __2RR: 2Rr: 0rr__ Phenotypic Ratio: __2 red: 2 pink: 0 white_ R RR RR r Rr Rr

7 Mendelian Genetics 1/1/2019 Codominance Codominance – Both alleles share dominance and are always expressed if present. Ex: In chickens BB = black feathers bb = white feathers Bb = black AND white feathers

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

9 CODominance Key: BB = black bb = white Cross: BB x bb B b b Bb
Mendelian Genetics 1/1/2019 CODominance Key: BB = black bb = white Cross: BB x bb B b b Genotypic Ratio: 0BB: 4Bb: 0bb Phenotypic Ratio: 0 black: 4 black and white: 0 white Bb

10 Mendelian Genetics 1/1/2019 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 B b B BB Bb b Bb bb
Mendelian Genetics 1/1/2019 CODominance Practice: Cross two black and white feathered chickens. Give the expected phenotypic and genotypic ratios of the offspring. B b Key: BB = black bb = white Bb = black and white Cross: _Bb x Bb__ Genotypic Ratio: __1BB: 2Bb: 1bb__ Phenotypic Ratio: _1 black: 2 black and white: 1 white_ B BB Bb b Bb bb

12 Law of Independent Assortment
Mendelian Genetics 1/1/2019 Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. This law can be illustrated using dihybrid crosses.

13 Mendelian Genetics 1/1/2019 Dihybrid Cross Tracks the inheritance of two traits. Ex. Seed shape and seed color Each pair of alleles segregates independently during gamete formation

14 All possible gamete combinations
Mendelian Genetics 1/1/2019 Dihybrid Cross Traits: Seed shape & Seed color Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations

15 Dihybrid Cross Gametes are placed in the punnett square RY Ry rY ry RY
Mendelian Genetics 1/1/2019 Dihybrid Cross Gametes are placed in the punnett square RY Ry rY ry RY Ry rY ry

16 Dihybrid Cross Put R’s back together and Y’s back together
Mendelian Genetics 1/1/2019 Dihybrid Cross Put R’s back together and Y’s back together RY Ry rY ry RY Ry rY ry RRYY Continue filling in the Punnett Square….

17 Dihybrid Cross RY Ry rY ry Genotypic Ratio: 1 RRYY: 2 RRYy: 2 RrYY:
Mendelian Genetics 1/1/2019 Dihybrid Cross RY Ry rY ry Genotypic Ratio: 1 RRYY: 2 RRYy: 2 RrYY: 1 RRyy: 4 RrYy: 2 Rryy: 2 rrYy: 1 rrYY 1 rryy RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy

18 Dihybrid Cross RY Ry rY ry Phenotypic Ratio: Round/Yellow: 9
Mendelian Genetics 1/1/2019 Dihybrid Cross RY Ry rY ry Phenotypic Ratio: Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 RRYY RRYy RrYY RrYy RRyy Rryy rrYY rrYy rryy

19 DIHYBRID PRACTICE 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:

20 OTHER PATTERNS OF INHERITANCE

21 Polygenic Traits “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___

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

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