Katherine may be alone in making people laugh with genetics material. Results of a web search included these little nuggets of hilarity: Q. Where would you find genes retired from the human genetic pool? A. In an old folks genome. Q. How do you tell the sex of a chromosome? A. Pull down its genes. Like, ha ha.

Apparently there's no such thing as a sense of humour gene. A now 9-year-old study revealed that sense of humour is pretty much entirely shaped by family and cultural environment.

Why do nature v nurture studies so often involve twins? According to Prof Alex MacGregor of St Thomas' Hospital Twin Research Unit, "Studying twins cuts down the 'noise' created by individual differences in environment and life experiences... You can control simultaneously for genetic background, sex, birthdate, pre-and post-natal environment and a host of other environmental factors." In other words, it helps rule out some non-genetic causes of differences between the people in the study.

But how reliable are twin studies in determining whether behaviour is genetic or environmental? Nay-sayers say that you can't assume that twins have shared the same environment: upbringing, diet, etc. Also twin studies may not apply to the rest of the population as twins are more likely than single babies to suffer complications during pregnancy and shortly after birth.

How come Katherine doesn't get nervous before a gig? Well - ta dah! - it could be down to her genes. A 2005 animal study suggests differences in the length of seemingly non-functional DNA, known as microsatellite or junk DNA, may explain why some people are shy and others the life and soul. Find out more here.

March 2008: Twin study reveals that our level of happiness throughout life is strongly influenced by the genes with which we were born.

September 2008: Twin study suggests that a man's reluctance to marry may be down to a genetic 'flaw'.