Note on the offspring of thoroughbred chestnut mares

Abstract

The colours of English throughbred race-horses, as recorded in Weatherby’s General Stud-Book, are grouped under the six main categories─Grey, Roan, Chestnut, Bay, Brown, Black ; but each category includes a considerable range of colour, and intermediates occur with quite sensible frequency. At the meeting of the Royal Society, held on December 7 last, the suggestion was made that the relation between the most important colours, Chestnut, Bay, and Brown, might be expressed by a simple Mendelian formula─Bay or Brown being regarded as determined by one Mendelian unit, which was “ dominant ” to the “ recessive ” Chestnut. In discussing this suggestion, I made certain statements, which I promised to justify as soon as possible, by offering the data, on which they were based, for publication. The object of the present note is partly to fulfil my promise, and partly to call attention to certain facts which must be considered in the attempt to apply any Mendelian formula whatever to the inheritance of coat colour in race-horses. I have taken from Weatherby’s Stud-Book a fairly complete record of all the foals produced in England by Chestnut mares during the period (rather more than eight years) covered by vols. 18 and 19. All cases of doubtful paternity have been excluded, and I have not tried to obtain external evidence in the few cases where the colour of sire or of foal is omitted. With these limitations, I believe the following statements are substantially complete and accurate.