Bayes 定理是概率论中最基本的定理之一。近年来,随着传染性等疾病被控制,遗传性疾病显得突出。在医学遗传学,尤其是遗传与优生咨询中,Bayes 定理的应用日渐增多,本文对此作一介绍。一、Bayes 逆概率定理概率是可能性或机会的定量计量。例如红细胞 MN 血型系统,有 M、N、MN 三种表型,每个人只能是其中一种表型。即三种表型是互不相容的。概率可以从随机取样调查的结果来估计。比如从中国汉族人 MN 血型分布(表1), Bayes theorem is one of the most basic theorems in probability theory. In recent years, genetic diseases have become prominent as communicable diseases are controlled. In the field of medical genetics, especially genetic and eugenics counseling, the application of Bayes theorem is increasing day by day. First, the Bayes inverse probability theorem probability is the probability or probability of quantitative measurement. For example, erythrocyte MN blood type system, there are M, N, MN three phenotypes, each person can only be one of the phenotype. That is, the three phenotypes are mutually exclusive. Probability can be estimated from the results of a random sample of surveys. For example, distribution of MN blood type from Chinese Han (Table 1)