Separation of the male and female flowers of corn and ease of distribution of corn seed from its origin in central Mexico to the various environments of the earth increased the genetic variability in the species. Selection by humans for those plants best fit for their individual use also reduced genetic variability of some other traits. Some favorable corn traits are expressed best when a specific gene pair includes at least one dominant form of a gene. But if the plant is heterozygous (one dominant and one recessive) for that gene, one quarter of the progeny created by pollination of the female flowers by pollen from the same plant will be homozygous recessive for that gene. That gene will not not be expressed in the plant growing from that seed.
Corn has a large number of genes and rarely does homozygosity of a detrimental recessive gene have an overwhelming affect on the plant, but accumulation of these events does detract from maximum growth and expression of favorable traits by corn. Regardless, the saving of seed in the various environments resulted in accumulation some homozygous recessive genes unique to that variety.
This is the enigma of selection of corn for uniformity that allows for uniformity of characters needed to get efficient and maximum harvest. Self pollinating preferred plants also increases the probability of eliminating the expression of favorable traits in the next generation. Selfing increases uniformity but detracts from many physiological processes involved in the ultimate goal of maximum grain yield. The boost in yield resulting from crossing plants from two of the distinct corn populations that were developed in different environments over many years apparently occurred because each had different negative recessive genes covered up by the dominant gene of the other population. The selfing process to obtain uniformity increased probability of negative traits but crossing with certain inbreds from another genetic family could overcome the negative traits of each.
Realization of this advantage of hybridization led to major advances in corn culture. Selfing of corn for favorable traits in today’s corn culture and hybridization with selected inbreds continues to lead to improved corn hybrids.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.