These two are also alleles because they code for genes that code for another trait, let's say, the color of the seed and so forth. Now, what exactly do we mean by a heterozygous organism? So, an organism is heterozygous if one of these genes in the pair of alleles is a dominant gene for that given trait, and the other one is a recessive one. So, what do we mean by dominant, and what do we mean by recessive? So, remember, according to the law of dominance, or Mendel's law of Dominance, the dominant gene codes for protein that inhibits the expression of that recessive gene. And so the recessive gene is never actually shown in the phenotype of that individual, and we'll see what that means in just a moment.