長子相続（ちょうしそうぞく）を英語でなんと言うか？

これはprimogenitureです。0:09 in Japan, it's Prince Hisahito, no his older sisters, who carries the monarchy's destiny. 日本では皇室の将来は悠仁親王に委ねられている。

http://www.youtube.com/watch?v=yOYEbN_D7BA 0:18 the 16 commonwealth countries which she is a head of state had decided to do away with the primogeniture rule and allow first-born daughters to automatically inherit the throne.
http://www.youtube.com/watch?v=cIApFA4Oi80 4:21 he's passed down the male line ever since.

参考リンク
http://bridge-english.blogspot.jp/2013/07/blog-post_2615.html  王位継承第三位を英語でなんと言うか？

練習問題解答
b-5055 male preference primogeniture