To locate genes associated with quantitative traits, geneticists often use QTL mapping (see the introduction to this chapter). To carry out QTL mapping, a first step is crossing two strains that differ in a quantitative trait, such as a strain of corn with high oil content and a strain with low oil content. The F1 progeny of this cross are then interbred or backcrossed to produce an F2 generation. Researchers then look for statistical associations between genetic markers and the value of the quantitative trait (e.g., oil content) in the F2 generation. Why do the geneticists look for statistical associations in the F2 plants? Why not use the F1 progeny?
Genetic Variation
Genetic variation refers to the variation in the genome sequences between individual organisms of a species. Individual differences or population differences can both be referred to as genetic variations. It is primarily caused by mutation, but other factors such as genetic drift and sexual reproduction also play a major role.
Quantitative Genetics
Quantitative genetics is the part of genetics that deals with the continuous trait, where the expression of various genes influences the phenotypes. Thus genes are expressed together to produce a trait with continuous variability. This is unlike the classical traits or qualitative traits, where each trait is controlled by the expression of a single or very few genes to produce a discontinuous variation.
To locate genes associated with quantitative traits, geneticists often use
QTL mapping (see the introduction to this chapter). To carry out QTL
mapping, a first step is crossing two strains that differ in a quantitative
trait, such as a strain of corn with high oil content and a strain with
low oil content. The F1 progeny of this cross are then interbred or
backcrossed to produce an F2 generation. Researchers then look for
statistical associations between genetic markers and the value of the
quantitative trait (e.g., oil content) in the F2 generation. Why do the
geneticists look for statistical associations in the F2 plants? Why not
use the F1 progeny?
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