Final answer:
An individual whose genotype is heterozygous for a gene carries one dominant allele and one recessive allele, generally written as 'Aa', and usually expresses the phenotype of the dominant trait.
Step-by-step explanation:
When an individual carries one dominant allele and one recessive allele for a gene, the individual's genotype is referred to as heterozygous. For example, if the dominant allele is represented as 'A' and the recessive allele is represented as 'a', then the heterozygous genotype would be written as 'Aa'. This means that the individual has two different alleles for the given gene on the homologous chromosomes. In most cases, the dominant trait associated with the 'A' allele will be expressed in the phenotype, meaning that the individual will outwardly show the dominant trait even though they also carry the recessive allele.