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Maize Genetics

There is a tremendous amount of genetic diversity in maize. Much of the maize you have seen may look the same, but across the world there are tens of thousands of  varieties of maize that are different colors, sizes, have different growing times, nutritional content, etc. Scientists at Cornell University are studying the diversity of maize, trying to connect two things: phenotype and genotype.

A phenotype is any physical attribute that can be measured (also known as a “trait”). It can be something you can see like how tall the plant is, what color the kernels are, or when the plant flowers. Phenotypes can also be things we can’t see, like how much protein is in a kernel, or how efficient the plant is at photosynthesis.

A genotype is the DNA; the genetic makeup of an organism. DNA sequencing allows us to read the billions of DNA letters that constitute the genotype. Geneticists study the phenotype of an organism and correlate it to it’s DNA sequence. Once researchers understand which sequences are associated with which phenotypes, they can start using varieties containing genotypes we want, and breed varieties with new and better phenotypes. So, what’s the process of linking phenotypes with genotypes?

If a scientist thinks a plant’s genotype is related to an important specific trait (i.e., a specific phenotype) they can test their hypothesis through genetics. They start by crossing two plants and see if their offspring exhibit the trait; depending on the cross, some may, some may not. Or they can sample the diversity of maize crosses that prior breeders and farmers have already created. Sequencing the DNA of all the plants allows geneticist to test the hypotheses that specific genes are responsible for specific phenotypes.

Geneticists have been using and improving this process to connect phenotypes with genotypes for decades. A recent example of the success of this process was in tackling Vitamin A deficiency, which is a serious problem in the developing world. By connecting genotypes to phenotypes scientist were able to identify two genes in maize that increase beta-carotene (provitamin A) content. Breeders created new varieties of maize that are currently being grown in Zambia, providing children better access to the nutrients they need to be healthy and thrive.

This project is in collaboration with the Paleontological Research Institution and funded by the National Science Foundation Plant Genome Research Program, Award 1238014: “The Biology of Rare Alleles in Maize and Its Wild Relatives.”

Additional Resources: The Maize Diversity Project