Corn  

 
Group3~Honors Biology~Fall 2006
The University of Arizona
line decor
  
line decor
 

 
 
INTRODUCTION

Our article title is “The Origin of the Naked Grains of Maize” which introduces the research performed to explain one aspect of the large variation between maize and Mexican teosinte from which maize was domesticated.  The paper goes into how maize has evolved from teosinte and the genetic experimentation performed in order to demonstrate that maize evolved from teosinte.  This is an interesting research topic because both of their genotypes are so similar yet their phenotypes are so dramatically different that it resulted in a question of whether maize did in fact evolve directly from teosinte and are members of the same species (Zea Mays) or if it is just a completely different species. 

Plant Morphology:

In order to fully understand the research done in the article, one must be familiar with general plant morphology.  Plant morphology basically means the structure of the plant and in our case, the form of corn plants.  First off, all plants consist of three different parts: roots, stems and leaves.  However, it should be remembered that even though all plants may consist of these three parts, this does not mean that the stems, leaves, and roots of each plant will look the same as the next.  Therefore, this should also be noted when viewing Zea Mays plants as well; not all corn plants are going to look the same.  We can show this by comparing the physical differences of maize and teosinte.  Modern maize presents itself with a single primary shoot which is a stem with all of its leaves, whereas teosinte presents itself with many lateral branches that have their own sets of leaves attached to them.  Another major difference is that Teosinte’s fruit (the individual kernels) is enclosed within a stony cupule covered with a glume.  The cupule is a bowl-shaped expansion of the stem in which the kernels are produced.  The glume is a lid-shaped leaf that grows up from the stem and covers the cupule.  In maize, the cupule and the glume are greatly reduced resulting in the fruit that is easy to grind and eat.   Teosinte and maize do not only differ from one another by physical comparison but also by how each reproduces. It is important to know that a kernel is a dry fruit that contains a single seed inside.  In teosinte, the kernels can be easily separated from the plant by means of wind or other forms of weather and this can cause the seeds to scatter and therefore result in the development of new teosinte plants.  Whereas, with maize, the seeds are incased in the fruit just like teosinte, however the seeds cannot easily separate from the cob (the stem on which the fruits are produced).  In addition, each ear of corn in enclosed in husks which are more modified leaves, trapping the kernels inside.  Therefore the reproduction of modern corn is completely dependent on people.

Genetics:

The results of genetic crosses between teosinte and maize in the 1960’s suggested that the major morphological changes in maize are due to mutations in just five genes. The researchers of this gene hypothesized that the cause of phenotypic change in maize resulted at the regulatory region.  The regulatory region is a segment of DNA in which proteins bind and thus control the gene expression of different aspects of the plant. Therefore, one goal of this study was to determine if the change between maize and teosinte was occurring within the regulatory region or was the result of an actual protein produced by this gene.

Why We Do Research:

The reason why research was done on this particular topic was because it was important to understand how a few mutations can lead to drastically different phenotypes.  With the knowledge obtained from the results of this experiment other plants may be able to be mutated to produce more desirable outcomes for mankind as well as obtain further knowledge on the results of mutations on plant morphology and how it plays a role in the evolution of plants.  The phenotypic mutations of maize and teosinte are also similar to the phenotypic mutations between dogs and wolves or even between mastiffs and Chihuahuas.