So, an individual or organism is said to be heterozygous for a given trait if one of the alleles is dominant while the other one is recessive. Now, usually, an uppercase letter is used to designate the dominant gene, and the lowercase letter is used to designate the recessive gene. Let's suppose we're dealing with these two genes, the alleles that are shown in purple. Let's suppose on chromosome number one, this chromosome, this gene is a dominant gene, and this is a recessive gene. And the way that we describe this situation here without actually drawing out these chromosomes is by using the following symbolism. So, the uppercase T basically describes this gene that is dominant for that trait, the height trade.