What do the following have in common: a mysterious dog which defecates by night on suburban lawns in Leicester; a car worker who wants to exhume a dead aristocrat; puzzled parrot-fanciers who cannot work out the sex of their birds; two Scottish families fighting over ownership of a Burmese cat; a Bangladeshi man trying to persuade the British immigration authorities that his son really is his son so he can enter the UK; a registered falconer who insists that his birds were bred in captivity and not taken illicitly from the wild; the man arrested for the murder of the French hitchhiker Celine Figard?
The answer is that the fate of all of them may turn on the outcome of DNA fingerprinting, forensic science's greatest breakthrough since the original inky science of fingerprinting was perfected at the turn of the century.
In recent months, DNA testing has emerged as a tool in a whole range of endeavours, using a sample obtained from saliva, hair-root, semen, blood, bones or any other part of the body. Police use it to screen large numbers of people in the hunt for perpetrators of serious crimes. Mothers use it to finger reluctant fathers in maintenance cases, and fathers in situations where they are denied access to their children. Courts use it to determine ownership of disputed animals.
The Russian authorities even persuaded the Duke of Edinburgh to have a DNA test so that they could test the bones in graves which they suspected to be those of Prince Philip's relatives - the family of the last Tsar of all the Russias, murdered in 1917.
There is even a use for DNA testing in supermarkets. Tesco and Marks & Spencer are trying out a DNA-fingerprinted spray which, triggered by an alarm, will douse shoplifters in their stores and which will mark the intruders as well as the goods and will rub off on to receivers, remaining visible to police under ultra-violet light for six months.
All this new-found power to prove depends upon the double-helix structure of deoxyribonucleic acid (DNA) which is found in the chromosomes of all body cells. This is the chemical that carries the coded instructions which lay down an individual's genetic blueprint; with the exception of identical twins, no two people have the same genetic code.
The possibility of using DNA as an identification tool came about in 1984 when Professor Sir Alec Jeffries, a geneticist at Leicester University, discovered among the three billion base units which make up a DNA molecular chain the bits which distinguished between individuals. The technique of DNA profiling which he then developed is far more versatile than fingerprinting. In the case of birds a DNA profile can now even be detected from the feathers, thanks to a technique developed by Dr David Parkin, senior lecturer in genetics at Nottingham University. His work has been the basis for a nationwide police campaign against collectors who claim they have bred rare birds like peregrine falcons, goshawks, golden and sea eagles from parents held legally under Department of the Environment registration, but who may have removed them from the wild. Suspicions that many such birds are taken illicitly from the wild could not, until recently, be proved.
"Before the DNA test was developed it was often difficult to prove a breeder was lying," says Dr Parkin. He has now been approached by experts from the dog world who suspect that a top Highland White terrier breeder is passing off bought-in puppies and claiming they are sired by his champion dog. There is even one irate character locally who wants to use DNA testing on dog dirt to find out whose animal has been misbehaving on his lawn.
"You could genetically fingerprint dog turds," Dr Parkin sighs. "There is bound to be some mucus on them containing cells from the bowel of the animal. But really you'd be better off sitting up and looking out of the window until you spotted it. …