For example, when he bred plants that had green pea pods with plants that had yellow pea pods, all of the offspring had green pods. A trait that disappeared in one generation could reappear, unchanged, in the next. Mendel reasoned that since traits are inherited in a discrete form, then hereditary information must also come in discrete parcels that are passed down unchanged from generation to generation. What makes individuals different is that a gene can have several different forms, or alleles. Thus, in peas, the pod color gene has green and yellow alleles, the plant height gene has tall and dwarf alleles, and so on.
Individuals have two copies of each gene, one inherited from each parent.
How the two copies interact with each other determines an organism's characteristics. What matters is how many of which type of allele an individual gets. Mendel laid the foundation for our understanding of this business. Mendel's pea pods Only individuals that inherit two recessive alleles show the recessive form of a trait. Sickle cell is a recessive disease, while Huntington's is dominant.