Question

What is the difference between a gene and an allele in biology?

I understand that a gene is the coding for a particular trait but I don't really understand how an allele and a gene are different? All I am told is that an allele is the alternate form of a gene? Can someone please give me an example?

Answer 1

The difference between gene and allele can be understood with the the help of an example as explained below.

Explanation:

It is true that a gene is coding for a particular trait and an allele is the alternate form of a gene.

Let us take example of pea plant on which Mendel worked and proposed Laws of inheritance.

In pea plant a gene controls the height of the plant, whether it is tall or dwarf. Mendel observed as many as seven different traits in pea plant like height , color of flower, color of cotyledons, shape of cotyledons, etc. All these traits have clear cut alternative expressions. Plant can be tall or dwarf, bear purple or white flower, have yellow colored cotyledons or green colored ones, etc.

Each of these traits is controlled by a specific gene.

Gene controlling height can occur in two forms , one making the plant tall and the other dwarf.

Similarly gene controlling flower color occurs in two forms, one making the flower purple and the other white and so on for all other traits.

These alternate forms of each gene are called alleles. So each gene has two alleles.

The genes are located on chromosomes on specific location. In diploid organism, each cell has two sets of chromosomes, one each inherited form each parent. The two chromosomes of a homologous pair have identical genes at corresponding loci. However, the genes on two chromosomes, representing same trait my have same allele or alternate allele.

For example in pea plant allele T Makes plant tall and allele t makes the plant dwarf. T allele is dominant allele and t allele is recessive allele.

The plant will be homozygous tall (TT) if both the alleles of height are same and heterozygous (Tt) if two alleles are different. Both these plants will be tall as allele T (dominant allele) dominates over allele t (recessive allele).

I hope now you may be clear about the difference between gene and allele as I tried to explain with the help of specific example. You are welcome to ask me if still you have some doubt.