Mendel's law of segregation states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization. There are four main concepts involved in this idea. They are:
1. There are alternative forms for genes. This means that a gene can exist in more than one form. For example, the gene that determines pod color can either be (G) for green pod color or (g) for yellow pod color.
2. For each characteristic or trait organisms inherit two alternative forms of that gene, one from each parent. These alternative forms of a gene are called alleles. The F1 plants in Mendel's experiment each received one allele from the green pod parent plant and one allele from the yellow pod parent plant. True-breeding green pod plants have (GG) alleles for pod color, true-breeding yellow pod plants have (gg) alleles, and the resulting F1 plants have (Gg) alleles.