Agriculture Reference
In-Depth Information
C. Phenotypic Characterization of the Population for the
Trait of Interest
Phenotyping is a key component in any kind of mapping. It is the main
parameter to the power and accuracy of an association study. Phenotyp-
ing for AMoften involves a relatively large number of diverse accessions,
phenotypic data collection, and adequate replications across multiple
years and multiple locations (Rafalski 2010). However, these are gener-
ally no more onerous than in QTL mapping. In addition, when coupled
with a breeding population that will be extensively phenotyped for
selection purposes, the phenotyping for AM compares favorably with
that for QTL mapping with biparental populations. Typically, when
phenotyping for QTL in biparental populations, a wide range of phe-
notypes is displayed, andmany poor genotypes occupy space in the
eld
experiment or lab assay. Therefore,
ll all QTL
mapping requirements in terms of repetitions, environmental sampling,
and heritability have been dif
field experiments that ful
cult to conduct due to the high cost of
phenotyping both favorable and unfavorable individuals from a map-
ping population. AM, while also expensive in phenotyping, can be made
more ef
cient by only evaluating a sample of genotypes that have a
breeding purpose.
A rapid increase in the quantity of phenotyping data is likely soon but
data quality will still be a critical issue. The degree of environmental
effects in
uences the number of replications under different environ-
ments that are needed. The ideal is to have for each individual a mean
phenotype that is less biased by environmental effects or by measure-
ment errors (Ingvarsson and Street 2010). Accuracy in phenotyping
depends on the repeatability of
field or greenhouse conditions.
has started to play a central role
in science. Phenomics borrows techniques of noninvasive research from
medicine such as tissue imaging, infrared cameras to scan temperature
pro
In recent years, the term
“
phenomics
”
les, spectroscopes to measure photosynthetic rates, light detection
and ranging (LiDaR) equipment to measure growth rates, and magnetic
resonance imaging to reveal root physiology (Finkel 2009). All the
information (phenotypic and environmental) should be stored in a
database of each particular trait especially for complex quantitative
traits that will exhibit different components.
D. Assessment of the Association Between Genotypes and Phenotypes
The main objective of association studies is to identify patterns of poly-
morphism that vary systematically between individuals with different
