关于遗传力常见的误解

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大家好，我是邓飞，今天看了一篇非常好的文章，介绍了遗传力相关概念和计算方法，里面提到了常见的误解，这里汇总一下。

文献链接：https://excellenceinbreeding.org/sites/default/files/manual/EiB-M2_Heritability_18-02-20.pdf

在这里插入图片描述

1. 作者和单位

作者：

单位：

2. 文章简洁和目的

在植物育种中，品种需要再多个环境多个年份进行测试，这些试验也叫多环境试验（multi-environment trial, MET），这里的年份、地点以及他们的组合统统成为环境。

为了比较MET试验的准确性，植物育种家常常需要计算狭义遗传力（narrow-sense heritability）和广义遗传力（broad-sense heritability）。

本篇文章有三个目的：

解释澄清遗传力的定义
介绍一下如何计算
如何评价遗传力

3. 开局一张图

遗传力是表型和育种值的回归系数

遗传力是相关系数的平方

遗传力乘以选择差就是选择相应。

4. 两套计算遗传力的体系

第一种，是计算方差组分，然后用重复数对残差进行调整，计算遗传力，这个也称为标准的方法。

第二种，是计算BLUE值的标准误用于计算残差方差组分，这个也被称为piepho的遗传力计算方法。

5. 几种常见的对遗传力的误解

5.1 错误1：遗传力表示有多大程度上受基因决定

A heritability of x indicates that x% of the trait is determined by
genetics。

这是一个非常常见的误解，它源于对遗传力定义的误解。一个遗传力为0.40意味着该性状的所有表型变异中有40%是由于该性状的基因型变异所导致的。这与错误的理解有重要区别，即在每个植物中，40%的特征表现是由基因决定的，其余部分是由其他因素决定的。

原文：

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

要弄清楚这个错误理解，要从遗传力的公式得到，遗传力是遗传方差占表型方差的百分比，如果这个群体没有变异，那么计算遗传力就为0。但是不能表明不受基因控制。

5.3 误解3：遗传力低意为着基因型变异小，差异小

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.

这还要从概念上讲，遗传力=基因型方差组分/(基因型方差组分+残差方差组分），有可能残差方差很大，比如环境间差异很大，也会导致遗传力偏低。

5.4. 误解4：遗传力是固定的值

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.

遗传力与计算的群体规模、群体类型都有关系，而且随着群体结构的变化，遗传力估计也会改变。所以，要隔一段时间进行遗传评估。

飞哥注：一般育种群体中，遗传力的计算有一个区间，主要是判断数据收集是否异常。

5.4 误解5：高的遗传力，意味着有主效基因控制

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.

遗传力量化了表型的遗传信号，并不意味着它能说明该特征的遗传继承方式。无论是一个还是成千上万个基因，无论它们的效应如何，我们都可以得到高或低的遗传力。像眼睛颜色这样的主要-QTL特征，如果被研究的人群只有一种类型的眼睛颜色，遗传力可能很低；如果我们观察到所有类型的颜色，遗传力可能很高。像产量这样的高度定量特征，如果实验进行得好，有适当的复制水平，那么可以有高的遗传力；但如果农艺管理不良，遗传力也可能很低。

飞哥注：这肯定是广义遗传力的结果，事实上根据基因型数据计算的遗传力还是有参考意义的。植物中的MET试验的遗传力，是没有意义的。