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OTHER PATTERNS OF
INHERITANCE
1
LAW OF INDEPENDENT ASSORTMENT
 Alleles
for different traits are distributed
to sex cells (& offspring) independently
of one another.
2
SEX-LINKED TRAITS
 Trait
determined by a gene on a sex
chromosome (usually X).
Examples:
Colorblindness
Hemophilia
Muscular Dystrophy
SEX-LINKED TRAITS:
*Females must receive 2 affected X’s in order to
express the trait.
• Females with only 1 affected X are carriers.
• Males that receive one X from mother
expresses the trait.
SEX-LINKED PUNNETT SQUARE PRACTICE
Cross a colorblind mother with a father who
has normal vision: Give the genotypic and
phenotypic ratios.
Key: XcXc = colorblind mother XY = normal vision father
Cross: XcXc (x) XY
Xc
Xc
Genotypic Ratio:
X
Phenotypic Ratio:
Y
Answer on next slide…
5
SEX-LINKED
Key: XX = female
XY = male
Cross: XcXc (x) XY
X
Y
Xc
Xc
XcX
XcX
XcY
XcY
Genotypic Ratio:
2:4 XcX
2:4 XcY
Phenotypic Ratio:
2:4 Carrier Female
2:4 Colorblind Male
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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.

i
ii
8
BLOOD TYPE PUNNETT SQUARE PRACTICE
Cross a female who is Type AA with a male who is Type O (ii):
Give the genotypic and phenotypic ratios.
Key: AA = mother ii = father
Cross: AA x ii
A
A
i
Genotypic Ratio:
i
Phenotypic Ratio:
Answer on next slide…
9
BLOOD TYPE
Key: AA = female
ii = male
Cross: XcXc (x) XY
A
i
i
A
Ai
Ai
Ai
Ai
Genotypic Ratio:
4:4 Ai
Phenotypic Ratio:
4:4 Type A Blood
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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
W
W
Genotypic Ratio:
R
Phenotypic Ratio:
R
Answer on next slide…
12
INCOMPLETE DOMINANCE
Key: R = red
W = white
Cross: RR x WW
W
W
R
R
RW
RW
RW
RW
Genotypic Ratio:
0RR: 4RW: 0WW
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
X
16
CODOMINANCE
Cross a black (B) rooster 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…
17
CODOMINANCE
Key: B = black
W = white
Cross: BB x WW
W
W
B
B
BW
BW
BW
BW
Genotypic Ratio:
0BB: 4BW: 0WW
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: ________________________
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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
W
B BB
BW
W BW
WW
BW = black and white
Cross: _BW x BW__
Genotypic Ratio: __1BB: 2BW: 1WW_
Phenotypic Ratio: _1 black: 2 black and white: 1 white_
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