Download RRYY - Humble ISD

INCOMPLETE DOMINANCE
AND
CODOMINANCE
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INCOMPLETE DOMINANCE
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

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INCOMPLETE DOMINANCE
Cross a red (RR) snapdragon with a
White (WW) snapdragon. Give the genotypic and
phenotypic ratios.
Key: R = red flower W = white flower
Cross: RR x WW
Genotypic Ratio:
W
W
R
Phenotypic Ratio:
R
Answer on next slide…
3
INCOMPLETE DOMINANCE
Key: R = red
W = white
Cross: RR x WW
Genotypic Ratio:
W
W
0RR: 4RW: 0WW
R RW
RW
R RW
RW
Phenotypic Ratio:
0 Red: 4 Pink: 0 White
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INCOMPLETE DOMINANCE
Practice: Cross a pink snapdragon with a red
snapdragon. Give the expected phenotypic and
genotypic ratios.
Key: __________________
Cross: _________________
Genotypic Ratio: ________________________
Phenotypic Ratio: ________________________
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INCOMPLETE DOMINANCE
Practice: Cross a pink snapdragon with a red
snapdragon. Give the expected phenotypic and
genotypic ratios.
R
Key: R = red W = white RW = pink
R
R
RR
RR
W
RW
RW
Cross: _RW x RR__
Genotypic Ratio: __2RR: 2RW: 0WW__
Phenotypic Ratio: __2 red: 2 pink: 0 white_
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CODOMINANCE


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
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CODOMINANCE
Cross a black (B) chicken with a
white (W) chicken.
Give the genotypic and phenotypic ratios.
Key: B = black feathers W = white feathers
Cross: BB x WW
W
W
Genotypic Ratio:
B
Phenotypic Ratio:
B
Answer on next slide…
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CODOMINANCE
Key: B = black
W = white
Cross: BB x WW
W
B
B
BW
BW
W
Genotypic Ratio:
0BB: 4BW: 0WW
BW
BW
Phenotypic Ratio:
0 black:
4 black and white:
0 white
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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: ________________________
10
CODOMINANCE
Practice: Cross two black and white feathered
chickens. Give the expected phenotypic and
genotypic ratios of the offspring.
B
Key: B = black W = white
BW = black and white
Cross: _BW x BW__
W
B
BB
BW
W
BW
WW
Genotypic Ratio: __1BB: 2BW: 1WW_
Phenotypic Ratio: _1 black: 2 black and white: 1 white_
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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.
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DIHYBRID CROSS


Tracks the inheritance of two traits. Ex. Seed shape
and seed color
Each pair of alleles segregates independently during
gamete formation
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DIHYBRID CROSS



Traits: Seed shape & Seed color
Alleles: R round
r wrinkled
Y yellow
y green
RrYy
RY Ry rY ry
x
RrYy
RY Ry rY ry
All possible gamete combinations
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DIHYBRID CROSS
Gametes are placed in the punnett square
RY
Ry
rY
ry
RY
Ry
rY
ry
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DIHYBRID CROSS
Put R’s back together and Y’s back together
RY
RY
Ry
rY
ry
RRYY
Ry
rY
ry
Continue filling in the Punnett Square….
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DIHYBRID CROSS
RY
Ry
rY
ry
RY RRYY
RRYy
RrYY
RrYy
Ry RRYy
RRyy
RrYy
Rryy
rY RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
ry
Genotypic Ratio:
1 RRYY:
2 RRYy:
2 RrYY:
1 RRyy:
4 RrYy:
2 Rryy:
2 rrYy:
1 rrYY
1 rryy
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DIHYBRID CROSS
RY
Ry
rY
ry
RY
RRYY
RRYy
RrYY
RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
Phenotypic Ratio:
Round/Yellow:
9
Round/green:
3
wrinkled/Yellow: 3
wrinkled/green: 1
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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:

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OTHER PATTERNS OF INHERITANCE
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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___
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MULTIPLE ALLELES



Genes that have
more than 2 alleles
Ex: blood group.
There are 3 possible
alleles for this gene.
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