We generally characterize corn varieties by physical characters that we easily see. Plant height, grain color and hardness, ear height, standability and disease resistance are probably the characters we assume are mostly genetic expression. Each of these characters are mostly directly affected by 1-4 genes. The remaining 30000 genes in every corn plant are producing products not so easily observed but are really the ones affecting final hybrids performance.
The real action influencing everything the corn plant does is occurring in the cells. Not only are the 30000 genes in the cell nucleus on the 10 chromosomes being turned on at appropriate times to produce proteins active in cell metabolism but the DNA and RNA in cell organelles such as chloroplasts, ribosomes and mitochondria are active as well.
The breeding process eventually leading to developing inbred parents for hybrids offers many new combinations of the the genetics. Mutations naturally occurring along the way also contribute to genetic differences not easily detected visually. We may characterize hybrids by obvious features but inside the plant there are differences among hybrids. Although each plant is a single cross hybrid should be genetically identical, Individual plants within a breeding population is not.
It is much similar to the ease with which we classify individual humans by simple visible characters such as skin color or hair color without acknowledging that each individual is genetically different from the next person with same skin or hair color. We have between 20000 and 25000 genes in our chromosomes, and a couple hundred thousand years of genetic mutations within our species and apparently some crossing with related species along the way.
Just as with humans, corn genetics were affected by selection in specific environments. The resulting genetic diversity contributes to new combinations that will drive the future with important adaptations.
Corn Journal has discussed genetics that can be found in the search on Corn Journal page under genetics. One of those blogs from Corn Journal 9/14/2017 follows:
At least 32000 genes in the ten chromosomes plus the independent DNA of mitochondria and chloroplasts in corn plants. We know the function of relatively few of these genes. We have selected genetics based upon field performance for the traits that we desire for the most part but we don’t know the actual genes involved in establishing grain yield and standability. Certain physiological processes such as photosynthesis can be studies, discerning the enzymes that can be traced back to a genetic code. Based on mutations we can determine the genes involved in endosperm starch formation. Resistance to some diseases can be linked to specific genes.
But how about the genetics that determines number of stomata, allowing for passage of CO2 into the leaves, or loss of water. Do genetics influence the photosynthesis in stomata guard cells determining when they open or close? Chloroplast and mitochondria DNA influence the membrane structure of these organelles. Replication of chloroplasts and mitochondria must involve the interactions of genetics of these organelles with that of the host cells. Movement of minerals into cells and photosynthetic products out is partially determined by cell wall structures as influenced by genetics. Size and number of vascular bundles must be important to movement of water from roots to leaves and ears as well as carbohydrates from leaves to roots and ears.
Genetics influence corn stalk rind thickness, duration of life in pith cells and carbohydrate storage capacity. Root branching, formation of root hairs and ability to absorb water and minerals from the soil are affected by products of the corn plant’s DNA. Kernel number and size also limited by genetics. It is no wonder that corn has a lot of genes.
Many of these genes had to have been established in those Teosinte plants that humans tapped several thousand years ago. Natural occurrence of mutations and human selection of traits expressing adaptation to their environments and desires provide us with large genetic variability. Despite modern molecular techniques to study corn DNA, the complexity of interactions within the corn plants, we are still stuck with our somewhat crude method of field testing in several environments for the best hybrids. We do this with the knowledge that many unknown genes are influencing the final performance and the hope that there remain new genetic combinations that will lead to better performance in the future.
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.