Multiple alleles occur when there are more than two allelic forms of a given gene in a species. Examples include blood groups in humans and coat color in mice. The ABO blood group gene in humans has three alleles - IA, IB, and i - which determine blood types A, B, AB, and O. Coat color in mice is also determined by multiple alleles at a single gene locus, with alleles for black, brown, agouti, gray, and albino hair colors exhibiting a dominance hierarchy. Multiple alleles always influence the same trait and occupy the same locus on chromosomes, with no crossing over between member alleles of a multiple allelic series.

1. Multiple allele
Harshraj Subhash Shinde
KKW, CABT, NASHIK

2. Outline
• Introduction and Defination
• Features of Multiple allele
• Examples of Multiple allele
a. Blood group in human being
b. Coat colour in mice

3. Introduction
“Multiple allele- When more than two different form of
given gene exist in a species they are called as multiple allele”
• Normally individual has two alleles
• During his study on Genetic Mendel also assumed only two
alleles of one trait.
• There can be large number of possible allelic forms in that
same population. This situation is called as multiple allelism.

4. Features of Multiple Alleles
 Multiple alleles always occupy the same locus on the
chromosome.
 Multiple alleles always influence the same character.
 No crossing over among the member alleles of the same
multiple allelic series.

5. Examples of Multiple Alleles
a) Blood group (ABO) in human.
b) Coat color in mice.
c) Coat color in rabbit.
d) Eye color in Drosophila.

6. Blood group (ABO) in human
• Classical and most common example of multiple allele is ABO
blood group of human being
• Gene coding blood group has three alleles rather than two.
• For the ABO gene, the three alleles are the IA, IB and i alleles.
We typically call these alleles "A," "B," and "O,"
• “letter "I,“ stands for "immunoglobin."

7. Cont…
• The IA and IB show co-dominance - an individual who is
heterozygous for these two alleles, the phenotypes of both
alleles are completely expressed, thus producing blood type
AB.
• The i allele (the "O" allele) is recessive to both the IA and IB
alleles (the "A" and "B" alleles).
Sr.no Genotype Phenotype
1 IAIA or IAi Type A
2 IBIB or IBi Type B
3 IAIB Type AB
4 ii Type O

8. Coat color in Mice
• The coat or hair color in mice is determined by a single gene with a series
of alleles.
• Alleles for black, brown, agouti, gray, albino, and other colors of hair.
• These alleles follow order of dominance like agouti > black > albino.
• This means that agouti is dominant to black and albino; black is dominant
to albino.