時事問題と絡めて読んでみましょう
Those justifying a mate-only system routinely refer to an unbroken male line of 125 generations since Japan's first emperor Jimmu. Although the first ten or so generations are probably mythical, and there may have been a break after the 25th emperor, Japanese historians say they are confident that the line has been continuous (if not always directly father-to-son) for 100 generations, or since about 500 ad.
If that's true, the imperial Y chromosome should be largely conserved, say geneticists. Accumulated point mutations are probably negligible, and although inversions and deletions might have built up, the sequence should still be recognizable, says geneticist Yutaka Nakahori of Tokushima University.
A genetics expert consulted by the government committee told Nature that digging up emperors to analyse their DNA could show how far the Y chromosome stretches back, how much it has changed in that time, and whether the line has ever been broken. But he says he doesn't want to be named, much less involved in such a project, (or fear of being "assassinated". And Mark Jobting of Leicester University. UK, who studies Y-chromosome evolution, says that most nuclear DNA from 1500 years ago would have deteriorated: "You would be very lucky to get good Y data from your ancient emperor,"
An alternative to digging up graves would be to trace a tree of the imperial family by comparing the Y-chromosomes of distant living relatives to estimate when the oldest family member would have lived. Nakahori says he would love to do this, but realizes it would never be allowed by the Imperial Household Agency, which keeps a jealous guard on such matters.
[from Nature, 23 February 2006]
Y chromosome=Y染色体
point mutation=点[突然]変異
ある遺伝子内で起こった突然変異による変化が非常に狭い範囲に限定されているもの
inversion=逆位
染色体上の遺伝子座の配列が一部逆転したもの。
deletion=染色体欠失（chromosomal deletion)
染色体異常の一つの型であり，染色体の一部分が欠けていること
その他の語
deteriorate=劣化する
jealous=守るに汲々とした