Post on 20-Jan-2016
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Types of Dominance
Types of Dominance
Simple, Incomplete, & Co-dominance,
Multiple Alleles, and Polygenic Traits
Simple, Incomplete, & Co-dominance,
Multiple Alleles, and Polygenic Traits
Simple dominance Simple dominance is when one allele is
ALWAYS stronger than a second allele.
Genotypes RR and Rr would BOTH show the phenotype “ round”The recessive phenotype, “wrinkled”, will only show with genotype rr.
R r
r
R
RR
Rr
Rr
rr
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Simple dominanceo Genotypes present? _____ , _____,
and _____R r
r
R
RR
Rr
Rr
rr
o Phenotypes present? _______ and
o ________o Genotypic Ratio? _________________
o Phenotypic Ratio?
________________
RR Rr
1 RR: 2 Rr: 1 rr
3 Round : 1 Wrinkled
Simple dominanceo Traits that exhibit Simple
Dominance:
o Widow’s Peako Dimples or No Dimpleso Curly hair or Straight hairo Yellow or Green Peaso Wrinkled or Round Peas
Incomplete Dominance A third phenotype is produced, and is a
BLENDING of the two other alleles.
R R
W
W
WR
WR
WR
WR
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Incomplete Dominance
o Note: The alleles are represented differently
R R
W
W
WR
WR
WR
WR
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o Genotypic Ratio: _____________
o Phenotypic Ratio:
4 WR: 0 WW: 0 RR
4 Pink: 0 white: 0 red
Incomplete Dominanceo Traits that exhibit Incomplete
Dominance: o Snapdragon color (Red+White = PINK)o Sickle Cell Anemia (Sickle Cell+Normal =
some Sickle & some Normal)o Fur length in Rabbits (Long+Short =
Medium)
Co-Dominance Both alleles will express
themselves completely, NO BLENDING.
Examples:o Horse Coloro Blood Typeso Chicken
Color
Co-dominance
B B
W
W WB
B
WBWB
WB
Genotypic Ratio?
100% heterozygous
Phenotypic Ratio?
100% Speckled
Multiple Alleles Traits that can have many different
alleles (not just 1 dominant and 1 recessive)
Hair color in Mice: 5 allelesAgouti A; black Ab; albino Aa;
gray Ag; brown Abr
Blood Type in Humans: 3 alleles:Blood Type in Humans: 3 alleles: A= Type A blood (dominant)A= Type A blood (dominant)
B= Type B blood (dominant)B= Type B blood (dominant) O= Type O blood (recessive)O= Type O blood (recessive)
Genotypes Phenotypes
AA or AO Type A
BB or BO Type B
AB Type AB
OO Type O
Check out possible genotypes and phenotypes of blood:
If you have AB as your genotype, you If you have AB as your genotype, you have both Type A and Type B blood, have both Type A and Type B blood, also known as Type AB also known as Type AB
If you have AO, O is recessive If you have AO, O is recessive to A, so you have type A blood to A, so you have type A blood
Q. When would you have Type O Q. When would you have Type O blood?blood?
A. When you have OO as your A. When you have OO as your genotype.genotype.
Blood exhibits both Multiple Alleles and Co-Domiance
Multiple Alleles: Blood Type
A A
B
B
AB
AB
AB
AB
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OA
B
O OO
BO
AO
AB
MANY DIFFERENT
GENOTYPES AND
PHENOTYPES!
Polygenic Traits Traits that are
affected by more than one GENE
Examples: Skin Color (2
genes)
Key# Genotype Phenotype1 M1M1M2M2 Black Skin2 M1M1M2m2 Dark Brown Skin3 M1M1m2m2 Brown Skin4 M1m1m2m2 Light Brown Skin5 m1m1m2m2 White Skin
Polygenic Traits – traits controlled by 2 or more genes that interact, forming the trait Usually show a wide range of
phenotypes Ex: Skin color, eye color, foot size,
height Wide range of skin colors because
there are more than 4 genes that control this trait.
Nature vs. Nurture Traits may be influenced by the
environment, for example height. If not given the proper nutrition as a child, they might not be as tall as their genes dictate.