Which statement best describes the relationship between an allele and a gene?
a. an allele is a variation of a gene that can be expressed as a phenotype.
b. an allele is the part of a gene that attaches to messenger rna molecules.
c. an allele is a segment of a dna molecule that controls replication of a gene.
d. an allele is the primary protein made by a gene found in a developing embryo

(i did to know why the wrong answers are wrong.)