Opportunities for mutations occurs with every cell division but those that really count are those that occur during meiosis, in which all cells dividing from the fertilized egg cell will lnclude the new DNA arrangement for that segment of the chromosome.
Corn advanced from that first mutation in Teosinte, allowing and exposed kernel to be easily used as grain. More mutations that occurred with each annual reproduction was utilized by people over the past 9-10000 years. Mutations occur naturally in all organisms. For example, each new human baby, on average, has 100-150 new mutations different from either parent. Majority of the human mutations are unnoticed and insignificant but a few can be drastic. But human generation reproduction is once every 20 years whereas an annual plant such as corn produces new mutants with each seed generation. Although the mutation rate per gene may be low in comparison with some organisms, having 32000 genes allows for a probability of some mutations to occur with each generation. Not all of these mutations will be expressed because they will usually occur in one strand of the paired DNA strands, allowing the other dominant version of the gene to affect the trait associated with the gene.
Mutation causes are associated with errors that can happen during meiosis and recombination of gametes during reproduction. Point mutations occur when a different nucleic acid is substituted during DNA replication. This small change can code for a different amino acid when placed in the eventual protein produced from the DNA-RNA-protein process. This can lead to a difference in some biochemical process that the original protein, acting as an enzyme, would affect. It may affect drastic and very visible differences in the plant but in most cases, it is insignificant and not noticed by most observers. Point mutations are probably the most common cause of mutations but a few other more drastic causes can be related to major errors in DNA duplication as part of meiosis. It is common, however for some breakage in one of the pair allowing a segment to be exchanged with a portion of the member of that pair. This process, called a crossover, is utilized by corn breeders in backcrossing procedures in which the objective is to cross a specific gene, such as a BT gene, into a desirable inbred without disturbing most of the genetics of the original inbred. Backcrossing in a gene, long used as a breeding procedure before use of GMOs, has been relatively successful in recovering the essential genetics of the original inbred but now with the desired gene such as the Ht gene for resistance to the fungus causing northern leaf blight or wx (waxy corn gene).
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.