The two copies or forms of a gene for one trait are called

The two copies or forms of a gene for one trait are called alleles.

Explanation:

Alleles of a gene are formed due to a mutation at same locus of chromosome.Alleles can be a) dominant,

                                 b)recessive or

                                  c) null alleles.

A dominant allele always expresses itself in the phenotype and masks the effect of recessive allele.The recessive allele could express itself only in the absence of dominant allele.A null allele is the one that lacks the normal gene function.

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