Somatic mutations：

　　A change in the genetic structure that is not inherited from a parent, and also not passed to offspring, is called a somatic cell genetic mutation or acquired mutation

A germline mutation is any detectable and heritable variation in the lineage of germ cells. Mutations in these cells are transmitted to offspring, while, on the other hand, those in somatic cells are not. A germline mutation gives rise to a constitutional mutation in the offspring, that is, a mutation that is present in virtually every cell. A constitutional mutation can also occur very soon after fertilisation, or continue from a previous constitutional mutation in a parent

这个网站对somatic mutation 和germline mutation 区别讲得很清楚：http://www.ncbi.nlm.nih.gov/books/NBK21894/

几个mutation概念