Final answer:
An individual with two different alleles for a particular gene is known as heterozygous, which typically involves one dominant and one recessive allele, with the dominant trait often being expressed in the phenotype.
Step-by-step explanation:
If an individual has two different alleles for a gene, he/she is heterozygous. Essentially, heterozygous refers to having two different alleles for a given gene on the homologous chromosomes. A person with a heterozygous genotype may carry one dominant and one recessive allele for a certain trait. This means the phenotype, or physical expression, will usually show the dominant trait. However, there are cases such as incomplete dominance or codominance, where both alleles influence the phenotype.