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OTHER PATTERNS OF INHERITANCE. Alleles for different traits are distributed to sex cells (& offspring) independently of one another. Law of Independent Assortment. Sex-Linked Traits. Trait determined by a gene on a sex chromosome (usually X ). Examples: Colorblindness Hemophilia - PowerPoint PPT Presentation
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OTHER PATTERNS OF INHERITANCE
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Alleles for Alleles for differentdifferent traits are traits are distributed to distributed to sex cellssex cells (& (& offspring) offspring) independentlyindependently of of one another.one another.
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Trait determined by a gene on a sex chromosome (usually X).
Examples:Colorblindness
HemophiliaMuscular Dystrophy
*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.
Cross a colorblind mother with a father who has normal vision: Give the genotypic and phenotypic ratios.
Key: Key: XXcXcXc = colorblind mother XY = colorblind mother XY = normal vision fatherCross: XcXc (x) XY
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Xc Xc
X
Y
Genotypic Ratio:
Phenotypic Ratio:
Answer on next slide…
SEX-LINKEDSEX-LINKED
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XcXXcX
XcYXcY
XcXXcX
XcYXcY
XX
YY
XcXcXc
Key: XX = female XY = maleCross: XcXc (x) XY
Genotypic Ratio:2:4 XcX 2:4 XcY
Phenotypic Ratio:2:4 Carrier Female2:4 Colorblind Male
“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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Genes that have more than 2 alleles
Ex: blood group.
There are 3 possible alleles for this gene.
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i
ii
Cross a female who is Type AA with a male who is Type O (ii): Give the genotypic and phenotypic ratios.
Key: Key: AAAA = mother ii = mother ii = fatherCross: AA x ii
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A A
i
i
Genotypic Ratio:
Phenotypic Ratio:
Answer on next slide…
BLOOD TYPEBLOOD TYPE
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AiAi
AiAi
AiAi
AiAi
ii
ii
AAA
Key: AA = female ii = maleCross: XcXc (x) XY
Genotypic Ratio:4:4 Ai
Phenotypic Ratio:4:4 Type A Blood
INCOMPLETE DOMINANCEINCOMPLETE 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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Cross a red (RR) snapdragon with a White (WW) snapdragon. Give the genotypic and phenotypic ratios.
Key: R = red flower WKey: R = red flower W = white flower
Cross: RR x WW
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W W
R
R
Genotypic Ratio:
Phenotypic Ratio:
Answer on next slide…
INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE
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RWRW
RWRW
RWRW
RWRW
RR
RR
WWW
Key: R = red W = whiteCross: RR x WW
Genotypic Ratio:0RR: 4RW: 0WW
Phenotypic Ratio:0 Red: 4 Pink: 0 White
INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE
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Practice: Cross a pink snapdragon with a red snapdragon. Give the expected phenotypic and genotypic ratios.
Key: __________________
Cross: _________________
Genotypic Ratio: ________________________
Phenotypic Ratio: ________________________
INCOMPLETE DOMINANCEINCOMPLETE DOMINANCE
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Practice: Cross a pink snapdragon with a red snapdragon. Give the expected phenotypic and genotypic ratios.
Key: R = red W = white RW = pink
Cross: _RW x RR__
Genotypic Ratio: __2RR: 2RW: 0WW__
Phenotypic Ratio: __2 red: 2 pink: 0 white_
RR
WW
RR RR
RRRR RRRR
RWRW RWRW
CODOMINANCECODOMINANCE 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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X
Cross a black (B) rooster with a white (W) chicken.
Give the genotypic and phenotypic ratios.Key: B = black feathers WKey: B = black feathers W = white
feathersCross: BB x WW
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W W
B
B
Genotypic Ratio:
Phenotypic Ratio:
Answer on next slide…
CODOMINANCECODOMINANCE
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BWBW
BWBW
BWBW
BWBW
BB
BB
WWW
Key: B = black W = whiteCross: BB x WW
Genotypic Ratio:0BB: 4BW: 0WW
Phenotypic Ratio:0 black: 4 black and white: 0 white
CODOMINANCECODOMINANCE
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Practice: Cross two black and white feathered chickens. Give the expected phenotypic and genotypic ratios of the offspring.
Key: __________________
Cross: _________________
Genotypic Ratio: ________________________
Phenotypic Ratio: ________________________
CODOMINANCECODOMINANCE
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Practice: Cross two black and white feathered chickens. Give the expected phenotypic and genotypic ratios of the offspring.
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_
BB
WW
BB WW
BBBB BWBW
BWBW WWWW