1.   But there might be some mistakes doing it this way, he says, because human genes are longer.

2.   Scientists continue to unravel the mysteries of human genes.

3.   The actual number of human genes is still in dispute.

4.   Animals may be given human genes to make their tissues compatible with humans, allowing animal hearts and other organs to be transplanted into critically ill people.

5.   The most advanced technology involves the use of viruses which have been engineered for safety and to accept human genes.

6.   A human gene can be inserted into fibroblasts using a retroviral vector, and the skin then grafted back to the donor.

7.   UK scientists led by Mr John Wallwork and Dr David White in Cambridge have succeeded in incorporating the human gene for DAF into pig DNA.

8.   The scientists hope to compile an electronic data base of human genes, so doctors around the world can have locations and descriptions of all known genes.