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Corn Breeding: Types of Cultivars: Overview and Objectives Ken Russell Department of Agronomy and Horticulture at University of Nebraska Lincoln, USA Leah Sandall Department of Agronomy and Horticulture at University of Nebraska Lincoln, USA The most common type of corn cultivar grown today and since the middle of the 20th century by U.S. farmers is the single-cross hybrid. In the 1930's and 1940's, double-cross hybrids were more prevalent. Before double-cross hybrids, farmers raised open-pollinated varieties. In this lesson, the development and production of these and other types of corn cultivars will be described. The advantages and disadvantages of other types of cultivars that could be grown by farmers also will be discussed. The lesson begins with a brief description of genes and alleles, which will be helpful in understanding some of the differences between types of cultivars. Objectives At the completion of this lesson you will be able to: Define gene, allele, locus (plural = loci), genotype, phenotype, homozygous, and heterozygous Describe heterosis and genetic segregation Comprehend the difference amoung the following types of cultivars: - inbreds - single-cross hybrid - double-cross hybrid - open-pollinated varieties - populations and synthetics - population x population crosses - inbred x population crosses