2020年江苏高考阅读理解C篇：

But it was the effects deep within the fat cells that may have been the most significant，the researchers found Multiple genes behaved differently，depending on whether someone had eaten or not before walking．Many of these genes produce proteins that can improve blood sugar regulation and insulin(胰岛素) levels throughout the body and so are associated with improved metabolic health．

请问and so are 这个分句的主语是什么？是Many of these genes 还是 proteins？

个人感觉proteins语义上比较顺。但是如果这么理解的话，and so are...这个句子则似乎应加上关系代词that以便和can improve...并列共同作为proteins的定语从句。

请高手赐教！