The Tetrarch a key sire in ensuring a lasting snowy legacy

1 Greyness in horses – as it is in the hair of men and women all over the world – is not a colour, rather an absence of the usual colour. The greyness 'gene' simply, slowly and remorselessly removes the original pigmentation from the horse's coat. Grey horses are thus born as horses of an entirely different colour before the de-pigmentation process begins. The majority of grey horses will end up as snowy as Father Christmas's beard, although some retain evidence of a darker shade. The greying rate differs sharply between individuals.

2 The grey gene is dominant, which means that where it is present it will be in evidence. This means that every grey horse must have at least one grey parent. A homozygous grey – one carrying two copies of the grey allele (one inherited from the sire, the other from the dam) – can only produce grey offspring.

3 It is believed that every grey thoroughbred can have its lineage traced back to one source – the grey eminence, so to speak. This great ancestor is Alcock's Arabian, probably born in Britain in the first years of the 18th century and also known as Pelham Grey Arabian or Bloody Buttocks. His influence was spread largely through the exploits of his son Crab, three times champion sire, and thence sideways through the pedigrees of greys up to the present day.

4 The influence of the outstanding The Tetrarch proved crucial for grey horses at a time when their numbers were dwindling. Known as The Spotted Wonder for his dramatically dappled coat and restricted to just seven unbeaten outings at two, The Tetrarch sired only 130 foals but he figures in the pedigrees of very many champions via his daughter Mumtaz Mahal's grandsons Nasrullah and Mahmoud, whose granddaughter Natalma produced the prepotent overlord of bloodstock Northern Dancer.

5 Only four greys have won the Derby, and none since Airborne in 1946. Just three greys have won the Grand National, the most recent being Neptune Collonges in 2012. Conversely, eight greys have won the Kentucky Derby and all since 1954, with the most notable being great champion Spectacular Bid in 1979 and filly Winning Colors nine years later.

Russe Blanc: the only horse registered as 'white' with Weatherbys

6 There are many greys but very, very few pure white thoroughbreds, who are characterised by being born with pale skin (grey horses have dark skin). The only white horse registered with Weatherbys is the Kerry Lee-trained French-bred chaser Russe Blanc.

7 Greys are more prone to suffering from melanoma (skin cancer) than other types of horse, with statistics indicating that more than three-quarters of grey horses over the age of 15 will develop melanoma, although the majority of tumours are benign.

8 Grey horses have their own race at Newmarket in August. Inaugurated in 2003, the Class 4 6f handicap owes its genesis to a similar race run in Melbourne and was only allowed to be run as long as a similar race for bay, brown and chestnut horses was also run on the same card.

9 Australia's favourite horse is grey. The sobriquet belongs to the 1992 Melbourne Cup winner Subzero, who was once the hack of Flemington clerk of the course Graham Salisbury but now spends his twilight years – he's 29 – visiting schools, hospitals and retirement homes, educating the young and bringing consolation to the lonely and unwell in his role as ambassador for Racing Victoria.

10 The world's leading prize-money earner Arrogate is a grey. He inherits his greyness from his sire Unbridled's Song, who was categorised as a roan in his passport but eventually turned white, which will be the fate of his great son one day. Arrogate is not the highest-rated grey, however – the snowy multiple Group 1 winner Daylami is ranked 2lb his superior on Racing Post Ratings.