Curiosity and the cat

A calico cat sounds like something out of a children's tale, but is in fact a descriptive term for a feline with mixed black and orange fur. If you already knew that, then you probably also know that calico cats are all female.

Well, not quite all, as Laura Gould found when the vet confirmed that her newly acquired calico was male. Satisfying her curiosity about how this rarity - known as George - came about, sent her on a long journey through university libraries and ultimately prompted this idiosyncratic book.

The result is an engaging popularisation of basic genetics laced with cat lore, tales from some by-ways from the history of science, and domestic minutiae from her cat-loving household. The vagaries of her quest also show how difficult it can be for even the most determined outsider to find a scientific answer to an apparently straightforward question. But find it she does, and her tale concludes when George's karyotype attests that his sex chromosomes have a most unusual configuration.

He is in fact a genetic mosaic. Half his cells have the normal male complement of sex chromosomes, a single X and Y. Half show up as XXY. This gives two ways of accounting for his coat colour, which is fixed by a gene on the X chromosome. If both the XX genes in the trisomic cells are the same, then they must both be different from the gene in the XY cells. Alternatively, if one is the same, the other must differ from the XY cells. Since one X chromosome in every trisomic cell will be inactivated, as happens in normal XX females, this will also yield a grown cat with a mosaic colouring.

Most male calicos are simply XXY - the trisomy that leads to Klinefelter's syndrome in humans, so George is more complicated than he might seem. So are other aspects of the story, including early attempts to unravel the genetics of calico cats, and more recent work on sex determination. These, intertwined with more familiar material about the history of Mendelian genetics, are a nice reminder that the early years of genetics were not the exclusive preserve of fruit fly fanatics, and that a perennial complication of biology is that different organisms present different obstacles to study.

The whole tale is very skilfully written, persuading one that George deserves his owner's intellectual attention. There are many more conventional popular introductions to genetics, but this one will attract some readers who are immune to the charms of other creatures, and offers a beguiling diversion for professionals. It is certainly a world away from all the breathless accounts of the human genome programme, with its high technology and attendant social concern. Gould implies that she had some trouble finding a publisher for her story. Springer have now found it a place in their new Copernicus popular science imprint. I am glad that they did.

Jon Turney is senior lecturer in science communication, University College London.