英语翻译However,some broods possess a few snails of the opposing

句子意思是：
但是,有时候一群蜗牛里会有一些反例,在主要都是左旋的一群蜗牛里,产生右旋的几率出乎意料的很高.
结构：
这是一个复合句,中间以and链接.
前半句：However,some broods possess a few snails of the opposing hand里possess是谓语,some broods 为主语,是说“有的（一）窝（蜗牛）”【你给的解释好像有点错哦,brood是窝的意思,snail是蜗牛】,小括号里是意译时补充进去的.snails 是宾语,of the opposing hand是描述snails的介宾短语.
后半句：in predominantly sinistral broods,the incidence of dextrality is surprisingly high.里逗号前的是介宾短语,逗号后是有谓语的句子.句子是主系表结构,the incidence 是主语,of dextrality 是解释/描述主语的介宾短语.