Multiple
Alleles
Multiple Alleles
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Mendel proposed that there are two alleles for every gene,
the dominant being expressed in a heterozygote
However, further studies into genetics shows that a gene can
have more than two allelic forms within a population
This does not mean that an individual possesses more than
two alleles. An individual can only have two of the alleles for
a specific gene, one maternal and one paternal
An example of multiple alleles of a gene is the C series in
dogs.
C is required for color while cc yields an albino. The
genotypes and phenotypes are as follows:
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C is a dog with color series expressed
cch is a chinchilla patterned dog
cd is a white dog with dark eyes
cb is a pale gray dog
c is an albino dog (pale eyes and nose)
Blood Types
Allele Antigen on RBC
IA
A
IB
B
i
none
Genotype
Phenotype
IA IA homozygous
Type A
IA i heterozygous
Type A
IB IB homozygous
Type B
IB i heterozygous
Type B
IA IB
Type AB
ii
Type O
Fun Fact: The “I” stands
for immunoglobin
Crosses Involving Multiple Alleles
Cross: a man who is homozygous
for blood type A with a woman
who is homozygous blood type B.
IA IA x IB IB
Cross: a man who is heterozygous
for blood type A with a woman
who is blood type O.
IA i x i i
Crosses Involving Multiple
Alleles
Cross: a man who is homozygous
for blood type A with a woman
who is homozygous blood type B.
Cross: a man who is heterozygous
for blood type A with a woman
who is blood type O.
IA i x i i
IA IA x IB IB
IA
IA
IB
IB
i
i
IA IB
IA IB
IA i
IA i
Type AB
Type AB
Type A
Type A
IA IB
IA IB
ii
ii
Type AB
Type AB
Type O
Type O
IA
i
Try one on
your own!
Cross: a man who is type AB
with a woman who is
heterozygous blood type B.
IA IB x I B i