When a plant is heterozygous, it has two different alleles for the same gene. The principle of segregation states that this will produce three types of gametes: AA, Aa and aa. The plant’s alleles for a specific gene will determine what gametes are produced. For example, if the allele is A and produces an AA gamete then all of the offspring from that parent will have at least one copy of A in their genome (no matter if they inherit it through maternal or paternal descent). \
This means that half of the children produced by this heterozygous organism would be homozygous dominant with AA genomes while the other 50% would be heterozygous with both alleles present. However, some genes can only produce two types of gametes: either AA or aa. When there are no combinations possible because each cell has just one type of chromosome, these organisms are called homozygous. There are also genes that can produce four types of gametes: AA, Aa, aA and aa. These organisms are called heterozygous for the gene in question because it is capable of producing two different alleles as opposed to one dominant type (called homozygous). Just like with the previous example if an organism has allele B and produces BA gametes then all children from this parent would be at least heterozygotes or have both alleles present.