Overview and Objectives
This is the second in a series of lessons specifically designed to instruct individuals without any formal training in genetics or statistics about the science of corn breeding. Individuals with formal training in genetics or statistics but without any training in plant breeding also may find these lessons beneficial.
The two ears in Figure 1 are from different corn plants. Would you be surprised to learn that the plant that produced the second and larger ear could be genetically inferior for grain yield than the first plant? How could this be true?
Figure 1: Two ears of corn harvested from two different plants that were grown in close proximity to each other. (UNL, 2004)
Plant breeders often work with traits, such as grain yield, that are controlled by many genes and/or are affected greatly by the environment. Such traits are known as quantitative traits, and the study of the inheritance of these traits is known as quantitative genetics. Because many traits that are economically important are quantitatively inherited, understanding quantitative genetics is important to plant breeders. In this lesson, some key concepts in quantitative genetics will be introduced, and these will give you some insight into the apparent paradox presented above.
Objectives
At the completion of this lesson you will be able to
- explain the difference between phenotype and genotype,
- explain the difference between qualitative and quantitative traits,
- explain the difference between micro-environmental and macro-environmental effects,
- discuss why breeders are interested in genotype and what they must do to measure genotypic value accurately,
- define the statistical concepts of mean and variance,
- define heritability, and
- explain why the heritability of a quantitative trait is important to a breeder wanting to modify that trait.