A(n) is a variation of a particular gene that may yield different outward characteristics in a person compared to someone with a different variation.

The correct answer is: Allele.

Explanation:

Alleles can be defined as different forms of the same gene.Each form encodes for a physical characteristics (external feature) that is different from the other form.In diploid organisms, alleles of many genes exhibit the property of Mendelian Law of Dominance.According to this law, the dominant allele is capable of expressing itself in the homozygous and heterozygous form of the genotype. The recessive allele is suppressed by the dominant allele and gets expressed only in homozygous form of the genotype.

Atissue is a group of connected cells that have a similar function within an organism.