Download Multiple Alleles and Polygenic Traits

Multiple Alleles and Polygenic
Traits
Multiple Alleles:
when more than two different
alleles exist for the same trait.
• (Remember: each individual will only have
two alleles for a trait but there are several
alleles to choose from.)
Rabbits, coat color
In rabbits, coat color is controlled by
multiple alleles.
• Full color (C), white (c), light-gray
or chinchilla (cch) and white with
black points or a Himalayan (ch).
Full color is dominant to all the other
alleles. Chinchilla is dominant to
Himalayan and white.
Cross a heterozygous Chinchilla
(cchc) with a heterozygous full color
h
with himalayan (Cc ).
cchc x Cch
ch
c
C
ch
c
ch
c
C
ch
ch
Cc
c
C
ch
ch
c
c
ch
Cc
Cc
ch
c
c
C
ch
Cc
Cc
ch
cchch
ch
c
c
C
ch
Cc
Cc
ch
cchch
chc
Genotypic Ratios:
ch
Cc :
ch
h
c c:
h
cc
1
1Cc : 1
1
Phenotypic Ratios:
2 full color: 1 Chinchilla: 1
Himalayan
In humans, blood type has multiple
alleles. IA and IB are codominant
and i (type O blood) is recessive.
Blood Type
Type A
Type B
Type AB
Type O
Type of Antigen
Possible Genotypes
Blood Type
Type A
Type B
Type AB
Type O
Type of Antigen
A antigen
Possible Genotypes
Blood Type
Type A
Type B
Type AB
Type O
Type of Antigen
Possible Genotypes
A antigen
IAIA, IAi
Blood Type
Type of Antigen
Possible Genotypes
Type A
A antigen
IAIA, IAi
Type B
B antigen
Type AB
Type O
Blood Type
Type of Antigen
Possible Genotypes
Type A
A antigen
IAIA, IAi
Type B
B antigen
IBIB, IBi
Type AB
Type O
Blood Type
Type of Antigen
Possible Genotypes
Type A
A antigen
IAIA, IAi
Type B
B antigen
IBIB, IBi
Type AB
Type O
A and B antigens
Blood Type
Type of Antigen
Possible Genotypes
Type A
A antigen
IAIA, IAi
Type B
B antigen
IBIB, IBi
A and B antigens
IAIB
Type AB
Type O
Blood Type
Type of Antigen
Possible Genotypes
Type A
A antigen
IAIA, IAi
Type B
B antigen
IBIB, IBi
A and B antigens
IAIB
Type AB
Type O
No antigens
Blood Type
Type of Antigen
Possible Genotypes
Type A
A antigen
IAIA, IAi
Type B
B antigen
IBIB, IBi
A and B antigens
IAIB
No antigens
ii
Type AB
Type O
Cross a heterozygous type A with a
heterozygous type B.
IAi x ___
Cross a heterozygous type A with a
heterozygous type B.
IAi x IBi
A
I
B
I
i
i
A
I
B
I
i
A
B
I I
i
B
I
i
A
I
i
A
B
I I
B
I i
A
I
i
B
I
A
B
I I
B
I i
i
IAi
A
I
i
B
I
A
B
I I
B
I i
i
IAi
ii
Genotypic Ratios:
A
I i:
A
B
I I
B
I i
1
1
:1
: 1 ii
Phenotypic Ratios:
1 Type A: 1 Type AB: 1 Type B:
1Type O
Cross a person with type AB blood
with another person with type O
blood.
A
B
I I
x ___
Cross a person with type AB blood
with another person with type O
blood.
A
B
I I
x ii
A
I
i
i
B
I
A
I
i
i
A
I i
B
I
i
i
A
I
B
I
A
I i
B
I i
A
I
B
I
i
A
I i
B
I i
i
IAi
A
I
B
I
i
A
I i
B
I i
i
IAi
IBi
Genotypic Ratios:
2
A
I i
:2
B
I i
Phenotypic Ratios:
2 Type A: 0 Type AB: 2 Type B: 0
Type O
Polygenic Inheritance:
the inheritance pattern is controlled
by two or more genes each with
two alleles.
In humans, eye color is the result of polygenic
inheritance.
• At the present, three gene pairs controlling
human eye color are known.
• Two of the gene pairs occur on chromosome
pair 15 and
• one occurs on chromosome pair 19.
Humans, eye color
• The bey 2 gene, on chromosome 15, has a
brown and a blue allele
• A second gene, located on chromosome 19 (the
gey gene) has a blue and a green allele.
• A third gene, bey 1, located on chromosome
15, is a central brown eye color gene.
• The brown allele is always dominant over the blue
allele so even if a person is heterozygous (one brown
and one blue allele) for the bey 2 gene on
chromosome 15 the brown allele will be expressed.
• The gey gene also has two alleles, one green and one
blue. The green allele is dominant to the blue allele
on either chromosome but is recessive to the brown
allele on chromosome 15.
• This means that there is a dominance order among
the two gene pairs. If a person has a brown allele on
chromosome 15 and all other alleles are blue or green
the person will have brown eyes.
• If there is a green allele on chromosome 19 and the
rest of the alleles are blue, eye color will be green.
• Blue eyes will occur only if all four alleles are for
blue eyes.
• Polygenic inheritance usually
shows up as a range of variation
such has height, skin color or hair
color.
• The results of an average
population will result in a bellshaped curve.
Phenotype = genotype + environment