11.   Often, genes play a factor.

12.   Other genes must also play a role.

13.   Pinpointing the genetic cause of asthma is difficult, however, because multiple genes play a role.

14.   Since the gene plays a role in normal cell division, extra copies may contribute to the uncontrolled growth of cancer cells, McGill said.

15.   So now scientists think that while genes may play some role, they might not be the sole controlling factor in tongue-rolling.

16.   The finding is expected to open an entirely new direction for research into the role that genes can play in turning normal cells malignant.

17.   The gene plays a vital role, when it is normal, in preventing cancer, but it causes many cancers when it is damaged.

18.   The fact is that we do believe that genes play a role, but only a role.

19.   As with cholesterol, genes play a role in elevated levels of homocysteine.

20.   Cowman said it is clear that another, as yet unknown gene plays a role in giving malaria resistance to chloroquine and artemisinin.