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Corn Breeding: Types of Cultivars

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Corn Breeding: Types of Cultivars - Summary and Definitions of Key Terms

Important types of corn cultivars are inbreds, single-cross hybrids, double-cross hybrids, and various kinds of populations. Differences among these types can be understood in terms of their genetics. For example, among these types only inbreds are pure-breeding. Any inbred has this characteristic because it is homozygous at all loci.

A hybrid is a cross between two genetically different plants. The most prevalent type of cultivar grown by U.S. farmers today is the single-cross hybrid. A single cross is produced by crossing two inbreds.

Corn hybrids generally are more vigorous than their parents. This increase in vigor is called hybrid vigor. When two inbreds are crossed that are not closely related, considerable vigor in plant and ear size relative to the parental inbreds is often observed in the single-cross hybrid. Usually a lesser amount of hybrid vigor is observed in other types of hybrids, such as a population x population hybrid or a population x inbred hybrid.

Key Terms

Gene - a unit of molecular information that controls cellular development and/or activity and is passed (inherited) from parent to offspring.

Locus - the specific site of a gene on a chromosome

Diploid - an organism with two copies of each gene

Haploid - an organism with a single copy of each gene

Allele - one of two or more alternative forms of the same gene

Homozygous - the descriptive term for a single-locus genotype of a diploid in which the two alleles are the same

Heterozygous - the descriptive term for a single-locus genotype of a diploid in which the two alleles are different

Inbred - a pure-breeding strain of corn

Single-cross hybrid - the type of hybrid that is produced when two different inbreds are cross-pollinated

Double-cross hybrid - the type of hybrid that is produced when two different single-cross hybrids are cross-pollinated

Population - a group of plants that are mating with each other and as a consequence have certain common characteristics

Hybrid vigor - the phenomenon of a hybrid plant having greater vigor than its parents

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