Here's a breakdown:

* Genotype: The genetic makeup of an organism, represented by the combination of alleles for a specific gene.

* Heterozygous: Describes a genotype where the two alleles for a particular trait are different.

* Alleles: Alternative forms of a gene that occupy the same locus (position) on homologous chromosomes.

For example, if a gene for flower color has two alleles: one for red flowers (R) and one for white flowers (r), a heterozygous genotype would be Rr. This individual carries one allele for red flowers and one allele for white flowers.

The phenotypic expression (the observable characteristic) of a heterozygous genotype depends on the dominance relationship between the alleles.