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Yet most ancestry testing only considers a single lineage,either the chromosome inherited through men in a father's line or mitochondrial DNA（mtDNA）,which is passed down only from mothers.

词汇：1.ancestry 世系

2. lineage 血统

3.chromosome 染色体

4. inherit 遗传

5. father's 男性祖先的

6.line  血统

7.mitochondrial 线粒体的

8.pass pass 遗传

主干：Yet most ancestry testing only considers a single lineage

同位语：either the chromosome or mitochondrial DNA（mtDNA）

过去分词作后置定语： inherited through men in a father's line

定语从句：which is passed down only from mothers

参考译文：但是，大部分世系检测只考虑一个单一的血统，要么是通过（ through）男性遗传的祖先（ father's）血统 Y 染色体，要么是只由（only from）母亲遗传的线粒体 DNA 。