“直系的”的英语可以翻译为：lineal，[法] direct ...

遗传不一定是直系的.Inheritance may not ascend linearly.我们都是直系的国际会员, 我们愿意在您参加门萨的过程中给您提供帮助.We also have coordinators in Beijing , Shenzhen . All of us are Direct International Member....