由于同卵双生的双胞胎基因完全相同，而异卵双胞胎不完全相同，所以研究人员可以分辨出决定某些性格特征及使人容易快乐的共同基因。

Because identical twins share the same genes and fraternal twins do not, the researchers could identify common genes that result in certain personality traits and predispose people to happiness.

youdao

然而近来出现了一个更加严重的问题：同卵双胞胎咋看之下并不完全一样。

A more serious one, though, has emerged recently. This is that identical twins may not be as identical as appears at first sight.

youdao

目前，人们对于转入的异质卵胞质中对胚胎的发生和发育造成影响的因素并不完全了解。

At present, how the heterogenous ooplasm influences the embryogenesis and development is not entirely clear.

youdao