396 



Prof. W. F. R. Weldon. Note on the [Jan. 15, 



sires giving foals of colour other than Chestnut, if each sire were capable of 

 giving 1 such foal in 60, would be 7'4/60 x 214, or about 26, the standard 

 deviation of the expectation being nearly 4 - 6 ; so that the result obtained is 

 not inconsistent with the view that any Chestnut horse is capable of pro- 

 ducing, by union with a Chestnut mare, a small proportion of foals of some 

 colour not Chestnut. If each sire had produced but a single foal, we should 

 clearly have to expect that only 1 she in 60 would produce a foal of abnormal 

 colour. Among the sires recorded, 56 have produced only a single foal each, 

 and of these foals one is Bay or Brown. 



On the other hand the Chestnut sires, Amphion and Despair, have 

 produced 115 foals, all Chestnut, while Amalfi, Brag, and Dog Rose have 

 together produced 36 Chestnuts and seven of other colours during the period 

 examined. 



We may conclude : (1) That the mean chance of obtaining a foal which is 

 not Chestnut from two Chestnut parents is about 1/60 ; and (2) that 

 this chance is not the same for all sires; it is probably less than 1/60 

 for Amphion, Despair, and their like, and much greater for such sires as 

 Amalfi, Brag, and Dog Rose. This variability in the power of transmitting 

 colours other than their own, possessed by Chestnut sires, is precisely what 

 Oalton's theory of dominance would lead us to expect ; it is, however, a 

 difficulty in the way of any Mendelian theory involving a reasonably small 

 number of elements. 



2. Chestnuts Mated with Bays and Browns. — On the view that Bay is a 

 Mendelian " dominant " to Chestnut, Bay sires should be sharply divided 

 into two series : those which are " hybrid," or of constitution " DR," giving 

 50 per cent, of Chestnut foals and 50 per cent, of Bays by the unions 

 considered, and those which are " pure dominants," giving only Bay offspring. 

 Any Bay horse with one Chestnut parent must be " hybrid " on this view ; 

 but it does not follow because both parents are Bay that a Bay colt is 

 a pure dominant. In the table below, those Bay sires which had either one 

 Chestnut parent, or were known to have produced a Chestnut foal, are classed 

 as " DR " ; while a Bay whose parents were both of some colour other than 

 Chestnut was classed as DD unless I could find a record that it had produced 

 a Chestnut foal. 



Among the 65 sires classed as DD, no less than 37 have produced only one 

 foal each during the period dealt with. Some of the sires are so young that 

 their whole progeny from Chestnut mares is too small to afford a test of their 

 real nature ; others are so old that the labour of testing them by reference to 

 previous volumes of the Stud-Book is great, and involves risk of error. For 

 such reasons as these, the number of sires classed as DD is certainly rather 



