If you've ever shared your home with more than one cat, you'll know how different their personalities can be. One might chirp for food, purr loudly on your lap and greet visitors at the door. Another might prefer quiet observation from a distance. So why do some cats become chatty companions while others seem more reserved? A recent study led by wildlife researcher Yume Okamoto and his colleagues at Kyoto University in Japan suggests that part of the answer may lie in cat genes. Cat owners from across Japan were asked to complete a questionnaire about their cat (the Feline Behavioural Assessment and Research Questionnaire), and to take a cheek swab from their pet to provide a DNA sample. The survey included questions about a range of cat behaviour, including purring and vocalisations directed at people. The researchers in the recent Japanese study focused on the cats' androgen receptor (AR) gene, located on the X chromosome. This gene helps regulate the body's response to hormones such as testosterone and contains a section where a DNA sequence is repeated. AR is an essential part of vertebrate biology. The most ancient form of AR appeared in the common ancestor of all jawed vertebrates, over 450 million years ago. AR controls the formation of male reproductive organs, secondary sexual characteristics and reproductive behaviour. The number of these sequences alters how responsive the gene is. Shorter repeats make the receptor more sensitive to androgens. In other species, including humans and dogs, shorter repeats in the AR gene have been linked with increased aggression and extraversion.