Multiple Allele

Most of the gene in two alternative forms called Alleles that controls the same genotype character but certain gene may exist in more than two alternative forms this form of allele is called multiple Allele.

Characteristics

• Multiple alleles always occupy the same locus on the chromosome.

• Because all the alleles of multiple series occupy the same locus in the chromosome, therefore no crossing over occurs within the alleles of the same multiple allele series.

• Multiple alleles always influence the same character.

• The wild-type allele is nearly always dominant.

• When any two of the mutant multiple alleles are crossed, the phenotype is a mutant type and not the wild type.

Examples of Multiple Alleles

• Blood group (ABO) in humans.

• Coat colour in Mice

• Coat colour in Rabbit

• Eye colour in Drosophila

Blood group in Humans

• A classical and most common example of multiple alleles is the ABO blood group of a human being.

• Gene coding blood group had three alleles rather than two.

• For the ABO gene, the three alleles are IA, IB, and i. We typically call these alleles A, B, & O.

• The letter 'I' stands for Immunoglobin.

• The IA and IB show co-dominance. For an individual who is heterozygous for these two alleles, the phenotypes of both alleles are completely expressed. Thus producing blood type AB.

• The allele i is recessive to both the IA and IB alleles.