21.   Then they pour a solution containing the gene copies over a nylon strip embedded with all the variants of the six genes.

22.   They are still experimenting with the other gene.

23.   This is phylogeny, or the drawing of family trees of the various genes found in present-day forms of life.

24.   Together the two genes account for the great majority of cases of hereditary breast cancer.

25.   Then they tried deleting three of the four genes.

26.   When the two genes combined, they would light up -- showing doctors where to operate.