Multiple Alleles or Polyalelia: what they are, examples and exercises

Multiple alleles or polyalleles occur when genes have more than two allelic forms.

In the case of multiple alleles, three or more alleles are present in determining a population character.

Remember, an allele is each of several alternative forms of the same gene that occupy a locus on the chromosome and play a role in determining the same character.

Diploid individuals always have two alleles of each gene. One from the father and the other from the mother.

When a locus on the chromosome can be occupied by a series of multiple alleles, the genetic variability of the population increases. This is because the amount of possible combinations between the alleles for each locus becomes greater.

How do multiple alleles arise in the population?

Multiple alleles are a result of the process of mutation that occurs in the genes.

know more about Genes and Chromosomes.

Multiple Allele Cases

rabbits coat color

To determine the coat color of rabbits, we can observe the genetic manifestation of four allele genes.

As alleles occur in pairs in individuals, there are 10 possible types of genotypes in rabbits for this gene, and 4 types of phenotypes:

Coat color genotypes and phenotypes in rabbits

Genotypes	Phenotypes
CC, CC^tea, Cc^H, Cc	Wild
ç^teaç^tea, ç^teaç^H and c^teaç	Chinchilla
ç^Hç^H and c^Hç	Himalayas
cc	Albino

The C gene is dominant over all the other three, the C^tea, dominant over the Himalayas and the albino.

Read too:

• Dominant and recessive genes
• chromosomes

Inheritance of blood groups in the human species

An example of polyallelia in humans refers to the gene that determines the blood groups of the ABO system.

At the ABO system there are three genes that will act in the formation of the blood type, the phenotype.

Are they, the genes I^THEI^B and i.

Relationship between genotypes and phenotypes in the ABO system

Genotypes	Phenotypes
I^THEI^THE or I^THEi	A group
I^BI^B or I^Bi	Group B
I^THEI^B	AB Group
ii	Group O

Learn more about ABO system and HR Factor.

Exercises

(UFSCar/2002) Regarding the ABO blood system, a boy, when undergoing a serological test, revealed an absence of agglutinins. His parents had different blood groups and each had only one agglutinin. The likely genotypes of the boy's parents are:

a) IBi - ii
b) IAi - ii
c) IAIB - IAi
d) IAIB - IAIA
e) IAi - IBi

See Answer

e) IAi - IBi

(UFRGS/2005) Suppose that in a certain diploid species there is a character related to a series of four alleles (multiple alleles). In a given individual of the referred species, the maximum number of alleles represented related to the character in question will be equal to:

a) 2
b) 4
c) 6
d) 8
e) 10

See Answer

a) 2

(UFRGS/2004) Rabbits can have four types of coat: chinchilla, himalayan, aguti and albino, resulting from combinations of four different alleles from the same locus. In one experiment, animals with different phenotypes were bred several times. The results, expressed in number of descendants, are shown in the table below. If the aguti parent animal from cross 1 is used to obtain offspring with the chinchilla parent from cross 4, what proportion of offspring can we predict?

a) 1 aguti: 1 chinchilla
b) 1 aguti: 1 himalayan
c) 9 aguti: 3 himalayan: 3 chinchilla: 1 albino
d) 2 aguti: 1 chinchilla: 1 himalayan
e) 3 aguti: 1 chinchilla

See Answer

d) 2 aguti: 1 chinchilla: 1 himalayan