Mendel’s concept of inheritance envisaged that each gene had two alternative forms or allelomorphs one being dominant and the other recessive i.e. one being wild and other mutant.
The term allele is used to apply to the members of a pair of contrasting genes having alternative phenotypic expressions.
These alleles segregate during meiosis and each gamete contain only one allele of each pair. It is also revealed that all the alleles of a given gene occupy the same locus on the chromosome but only one at a time.
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Alleles are the contrasting pair of genes located on the corresponding loci of the homologous chromosomes.
Mendelian heredity had only two alternative expressions or alleles. However, many genes can change in several different ways or changes. Those changes give rise to several alternative states which are called multiple alleles.
Multiple alleles is a series of three or more alternative forms of same gene occupying a single locus on the chromosome, e.g. albino series of coat colors in rabbits, eye color in Drosophila and blood groups in man etc.
Characteristics of multiple alleles:
1. Multiple alleles are always at the same location (locus) in the chromosome.
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2. Crossing over never takes place between multiple alleles.
3. Multiple alleles always affect a similar characters i.e. eye color, eye shape.
4. Wild type is always dominant to all others at the same locus. The other alleles show the dominance in the order given in series.
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5. When any two multiple alleles are crossed, wild is never produced but phenotype of mutant character is shown.