Question

Define allele.

Answer 1

Hint:Genes are the DNA sequences which control the traits of an organism. Allele is one or more variants of a gene. It occurs in pairs or multiple forms representing a gene. The alleles occupy the same position on the chromosome.

Complete answer:
To solve this question, we must know about the allele and its type.
Allele is also known as Allelomorphs. It is a pair of genes that occurs at a definite locus on a chromosome which controls a particular characteristic. For example eye colour etc.

The expression of a particular trait is called the phenotype whereas the combination of allele which an organism carries is called its genotype. For example genotype AA represents the phenotype eye colour. If the paired alleles are the same (AA) then the organism is called homozygous and if the alleles are different (Aa) then it is called heterozygous.

There are two types of alleles
i) Dominant
ii) Recessive
In a heterozygous pair, the one which is expressing the trait is called dominant and the other is called recessive.

Significance of alleles-
i) All genetic traits are controlled by alleles.
ii) Alleles are carried by individuals who are at their highest fitness. The alleles carried by less fit individuals are lost over generations.
iii) Certain mutations, crossing over or environmental factors change the expression of phenotypes or alleles.

Note:Some of the alleles are codominant which means neither dominant nor recessive gene expression. An example of Codominance in the ABO blood group system in humans.