Here's a breakdown:

* Gene: A segment of DNA that codes for a specific trait.

* Allele: A variant form of a gene. For example, the gene for eye color might have alleles for blue, brown, or green eyes.

* Heterozygous: An individual with two different alleles for a particular gene.

Example:

Let's say the gene for flower color has two alleles:

* P: Purple flower color

* p: White flower color

A flower with the genotype Pp is heterozygous for flower color. It carries one allele for purple flowers and one allele for white flowers.