Q.: The immigration services of several different countries have bought your software. Why?

A.: Well, in Denmark for instance, there is as law where if one person has gained legal entry, then certain relatives are allowed to immigrate, too. Well, in Somalia, where a lot of immigrants seem to come from, there's a very broad definition of ''family.'' A potential Somali immigrant to Denmark might feel he or she is entitled because of membership in the same clan. When that happens, the Danish authorities go to a DNA laboratory that uses my software and who I consult for, to check the odds of a direct relationship.

Q.: What is the most interesting thing you've learned about human beings from your work?

A.: That quite a bit of adultery is intrafamily. One of the problems that paternity labs come up with is where a man is accused of paternity, and upon testing, it seems that he shares a lot of genetic similarity with the child in question, but not enough to be that child's father. What is going on here?

In those cases, you always wonder if the man being sued is not a father, might he not be the uncle! An uncle would explain this evidence very well. So what we have is a woman who is having relationships with a husband and the husband's brother. My colleague Jeff Morris and I did an analysis some years ago in which we came to the conclusion that this kind of relationship happens in at least 1 percent to 10 percent of cases.

Q.: How did you develop this odd but interesting profession?

A.: I come from a mathematical family. My father taught and my mother was an artist and a politician -- she was mayor of Palo Alto. In my family, practical mathematics was frowned on -- statisticians, we didn't even talk of them. I find it rather amusing that I now do very practical mathematics.

But my history is this: I was in England during the Vietnam War, avoiding the draft, and making a kind of living by playing bridge for money. By the time the war was over, I returned to the U.S. and graduate school, and I started developing a career for myself as a software writer. The software writing led to creating this DNA software. It's become a full-time business -- the software, consulting, teaching. Basically, I'm a freelance mathematician.

Q.: Is freelance mathematics lucrative?

A.: It's not bad. I can do what I want, but I make less than most senior academics.

Q.: The murder case where most of us learned about DNA evidence was that of O. J. Simpson. How would you rate the presentation of DNA issues during that trial?