When a plant from an open-pollinated variety is self-pollinated, all the progeny resemble that plant, although they all differ from each other and from the parent plant to some extent. If one of the progeny plants is self-pollinated, the new progeny again differ from each other and from the parent plant, but the degree of the difference is not as great as occurred after the first self-pollination. If this process is repeated about seven times, then a plant known as an inbred is produced. An inbred is a pure-breeding strain of corn. This means that if an inbred is self-pollinated, all of the progeny will be genetically identical to each other and to the inbred parent.
This process of repeated self-pollinations is known as inbreeding. Inbreeding corn results in loss of vigor (Figure 9).