How are the terms gene, locus, and allele related?

Hint: Gene is the sequence of DNA that codes for a protein; Locus is the physical location of a gene on the chromosome while the allele is the alternative form of a gene.

Complete answer:
Gene is the sequence of DNA that determines the characters or features that are inherited by offspring from their parents. So basically gene is the physical and functional unit of heredity. The genes contain information on protein synthesis during translation. These proteins are responsible for various functional and structural characteristics of a person. The number of genes varies in different organisms and species.

There are two copies of each gene present in each person, one inherited from each parent. Most genes are the same in all people, but less than 1 percent of the total genes are slightly different between people which arises due to mutations in these genes. Alleles are that different forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features.

Each cell has two alleles (one from each parent) one dominant and one recessive. The one allele which can express itself in presence of another allele is called the dominant allele while one which cannot express itself in the presence of another is called the recessive allele.

The position of the gene on the particular chromosome is called the locus. Each gene possesses a different locus on the chromosome but the alleles are said to occupy the same locus on the chromosome.

Note: The organisms which have the same allele (dominant or recessive) on the homologous chromosome are said to be Homozygous while the organisms which have different allele on the homologous chromosome are said to be heterozygous.