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.