# 编者信息 熊荣川 明湖实验室 xiongrongchuan@126.com http://blog.sciencenet.cn/u/Bearjazz A measure of genetic distance (D) based on the identity of genes between populations is formulated. It is defined as D = -logeI, where I is the normalized identity of genes between two populations. This genetic distance measures the accumulated allele differences per locus. If the rate of gene substitution per year is constant, it is linearly related to the divergence time between populations under sexual isolation . It is also linearly related to geographical distance or area in some migration models. Since D is a measure of the accumulated number of codon differences per locus, it can also be estimated from data on amino acid sequences in proteins even for a distantly related species. Thus, if enough data are available, genetic distance between any pair of organisms can be measured in terms of D. This measure is applicable to any kind of organism without regard to ploidy or mating scheme. 提出了一种基于群体间基因一致性的遗传距离（ D ）度量方法。其公式定义为 D = -logeI ，其中 I 是两个种群之间基因的标准化一致性。这个遗传距离测量每个基因座累积的等位基因差异。如果每年的基因替换率是恒定的，那么它与性隔离下种群之间的分化时间呈线性相关。在一些迁移模型中，它也与地理距离或区域（大小）呈线性关系。由于 D 是每个基因座密码子差异累积数量的一个度量，因此它也可以基于蛋白质中氨基酸序列的数据来估计，即使对于远亲物种也是如此。因此，如果有足够的数据，任何一对生物体之间的遗传距离都可以用 D 来测量。这种测量方法适用于任何一种生物体，而不考虑染色体倍性或交配机制。 Nei M . Genetic Distance between Populations . The American Naturalist, 1972, 106(949):283-292.
# 编者信息 熊荣川 明湖实验室 xiongrongchuan@126.com http://blog.sciencenet.cn/u/Bearjazz A gene is a unit of hereditary information. Except in some viruses, genes are made up of DNA, a complex molecule that codes genetic information for the transmission of inherited traits. Alleles are also genetic sequences, and they too code for the transmission of traits. So, what it is the difference between a gene and an allele? The short answer is that an allele is a variant form of a gene. Explained in greater detail, each gene resides at a specific locus (location on a chromosome) in two copies, one copy of the gene inherited from each parent. The copies, however, are not necessarily the same. When the copies of a gene differ from each other, they are known as alleles. A given gene may have multiple different alleles, though only two alleles are present at the gene’s locus in any individual. Alleles can sometimes result in different phenotypes (observable traits), with certain alleles being dominant (overriding the traits of other alleles) or, in some cases, multiple alleles acting in a codominant fashion. An example of the latter is the human ABO blood group system, in which persons with type AB blood have one allele for A and one for B (persons with neither allele are type O). An example of dominant allele expression is flower color in pea plants. A plant with purple flowers actually has a genotype (genetic makeup) consisting of a gene with a dominant P and a recessive p allele. 基因是遗传信息的一个基本单位。除某些病毒外，基因是由 DNA 组成的，这种复杂的分子编码遗传信息，传递遗传性状。等位基因也是遗传序列，它们也编码遗传性状。那么，基因和等位基因的区别是什么呢？ 简言之，等位基因是基因的一种变异形式。更详细的解释是，每一个基因以两个拷贝的形式存在于特定的基因座上（染色体上的位置），每个都遗传自父母某一方的基因拷贝。然而，这些拷贝并不一定相同。当一个基因的拷贝彼此不同时，它们就被称为等位基因。一个特定的基因可能有多个不同的等位基因（种群视角），尽管在任何个体内的基因座上只有两个等位基因。 等位基因有时会导致不同的表型（可观察的性状），某些等位基因是显性的（凌驾于其他等位基因的性状），或者在某些情况下，多个等位基因以共显性的方式作用。后者的一个例子是人类 ABO 血型系统，其中 AB 型血型的人有一个 A 和 B 的等位基因（没有这两种等位基因的人是 O 型）。显性等位基因表达的一个例子是豌豆植株的花色。紫花植物实际上有一个显性 P 基因和一个隐性 P 等位基因组成的基因型（遗传组成）。 What’s the Difference Between a Gene and an Allele? https://www.britannica.com/story/whats-the-difference-between-a-gene-and-an-allele
标签: 基因座
