This is a very common misconception that arises from a misunderstanding of the definition
of heritability. A heritability of 0.40 indicates that 40% of all the phenotypic variation for that
trait is due to variation in genotypes for that trait. This differs importantly from the
misconceived understanding that in each plant 40% of the expression of the trait is due to
genes and the rest due to other influences.
飞哥注:遗传力是个群体的概念,不能具体到个体。应该是这个意思吧,感觉很绕,我也没有很理解。
5.2 误解2:遗传力较低,表明受基因决定少或者不受基因决定
Misconception 2. “A low heritability means that traits are not determined by genes”
A heritability that is larger than 0 always indicates that genes have an effect on the expression
of the phenotype. The heritability is determined by the proportion of genetic variance relative
to the phenotypic variance. A low heritability therefore can indicate that the genetic variance
is low compared to the phenotypic variance (both could be small). For example, branching in
maize is very much genetically determined, but because by far most genotypes used in
modern maize programs have a single stem, the genetic variance for branching is very low
Misconception 3. “A low heritability means that genetic differences are small”
A low heritability does not automatically indicate that the genetic variance is small; it can also
indicate that the error variance is large. This can be caused by high environmental influence,
for example, but also by inaccurate phenotype recording. For example, resistance to a certain
infection will depend on the genetic potential to withstand that infection; the problem is how
to measure that potential. If a single field measurement is taken of nematode infection in
beat plants, it will record only those infected at that time, but this could vary according to the
environment selected for recording infection levels.
Misconception 4. “A heritability is a fixed value”
The heritability reflects the relative weight of the genetic variance component in the
phenotypic variance of a specific population and is based on observations that were taken
on a specific moment in time. The magnitude of heritability depends on genetic variance in
a population, but also on the influence of the environment and on the accuracy of
observations (see misconception 3). The genetic variance in one population may be
(somewhat) different from that in another population. Finally, heritability within a population
can change over time, and for that reason, should be estimated at regular intervals.
Misconception 5. “A high heritability implies a major-effect QTL”
The fact that the heritability quantifies the genetic signal from a phenotype doesn’t mean
that says something about the genetic inheritance of the trait. Whether there’s one or many
thousands of genes behind and irrespectively of their effect we can have high or low
heritabilities. A major-QTL trait like eye color can have low heritability if the population
scanned have only one type of eye color, or a high heritability of we observe all types of color.
A highly quantitative trait like yield can have a high heritability is the experiment is well
conducted with high appropriate replication levels, but can also have low heritability if the
agronomic management is poor.