Changing a single gene can greatly alter a maize plant's appearance and function. A gene mutation on the plant's second chromosome, for example, will dwarf the corn, causing it to grow only a foot high in some cases.
To create a living maize chromosome map, a garden with 106 maize plants, each with a different type of mutation, has been planted at Cornell. The mutant plants are arranged in the same order in the garden as their altered genes occur on the maize plant's chromosomes.
The garden, in the Cornell Plantations Emerson Garden, across from the McClintock shed on Plantations Road, is a joint project of Cornell's Department of Plant Breeding and Genetics and the U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) at Cornell.
The garden actually recreates a maize-chromosome-map garden planted in 1932 in honor of the Sixth International Congress of Genetics held in Ithaca that year. The current garden will pay tribute to Cornell's pioneer maize geneticists, including Rollins A. Emerson and Nobel laureate Barbara McClintock, and next year, it will commemorate the 100th anniversary of Cornell's Department of Plant Breeding and Genetics and the 75th anniversary of the original garden at the 1932 genetics meeting.
Each plant in the garden reveals an obvious change that has been found in nature. "These are just mutants that are naturally occurring; it's not like somebody created them," said Margaret Smith, professor of plant breeding and genetics and the university's maize breeder. "There are a variety of naturally occurring mutations that show loss of function or show a difference in how the plant looks."
For example, when a particular gene on the short arm of chromosome four is altered, the plant's reaction to gravity -- its geotropic response -- is affected. Called "lazy plant," such corn grows horizontally along the ground. A gene mutation in chromosome three's short arm, on the other hand, causes the plant to more closely resemble tall grass, with little, thin leaves and many stalks.
To mimic the 10 chromosomes from each parent in the maize genome, the garden has been planted in 10 rows, each containing plants in sequence of their specific mutant genes.
The garden was planted in late June, more than a month later than when most maize experimental plots are planted in the Ithaca area.
"We wanted it to be looking good in September when students return, and professors can visit the garden with their students," said Denise Costich, a research associate with USDA-ARS and one of the principal organizers of the garden, which she expects to be visited by classes in genetics, plant breeding and agronomy.
"Seventy-five years ago the maize geneticists planted a garden like this with all the mutants they knew about then," said Smith. "It is kind of fun to recreate that and see how much richer our knowledge of maize genetics has become."
Since maize plants are annuals, the garden will be planted each year. Smith plans to conduct controlled self-pollinations, in which pollen from a mutant's tassels will be used to fertilize its own eggs in the ear, creating new kernels (seeds) that carry the same mutation.
Hank Bass, an associate professor of biological science at Florida State University, provided the starter seeds for the project.