Alleles – Class 12 | Chapter – 5 | Biology Short Notes Series PDF

Alleles: An allele is one of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location. An individual inherits two allele, one from each parent, for any given genomic location where such variation exists. If the two allele are the same, the individual is homozygous for that allele. If the allele are different, the individual is heterozygous.


All the allele found in an organism make up the genotype. If a pair of alleles are similar, the organism’s genotype is called homozygous. If the pair of allele are different, the organism’s genotype is called heterozygous. A dominant allele will overrule the characteristics of a submissive allele in a heterozygous genotype. But in some traits, an allele is neither dominant nor recessive. For example, the human blood group ABO.

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