Different froms of a gene for a given trait is called Alleles
Explanation:
A different form of Gene comes in differing varieties. These are called Alleles.
For every Somatic cell, every gene contains two alleles (each allele being provided by respective parents).
It is impossible to determine which allele is present of a gene in an organism based only on physical observation. While some alleles can be recessive and dormant and silently passed to the offspring generation.
Some Common example of varying gene traits is the colour of plants where one colour is often dominant and the other recessive while in some other plant the recessive colour can be dominant.
