The Inheritance of Red, Roan and White Coat Colour in Dairy Shorthorn Cattle

THE INHEI%ITANCE OF ~ED, ROAN AND I~q-IITE COAT COLOUP~ IN DAIRY SHORTHORN CATTLE ]3Y I. CHESTER JONES, Del~ar~ment of Zoology, University of IAver2ool (With Plates 6 and 7) I. INTRODUCTION In Shorthorns, in the vast majority of cases, both red and white animals breed true for co]our and crosses between them give roans. The simplest explanation is that red and white are allelomorphs, the heterozygote giving roan (Wilson, 1908; Smith, 1925; Roberts, 1937). Some workers, recognizing the fundamental redness of Shorthorns, have suggested theories to meet this. Walther (1913) argued that the oolour must. be 'a fixed red', the white 'moving over a large area'. He postulated one ]?air of allelomorphs, therefore, white and the absence of white. Crew (1925) suggested that 'all Shorthorns may be reds...' and looked upon white as due to a modifying factor. Wright (i917), considering, the production of some animals with red pigment in the F 2 generation of white Shorthorn by Galloway crosses, postulated two pairs of altelomorphs--E, a factor for black allelomorpkic with e, a factor for red, and W, white, atlelomorphic with w, the absence of white, the heterozygote Ww g/~,-ing roan. Ibsen (1933), also concerned with ~he Shorthorn by Galloway crosses, posttflates two pairs of aUelomorphs--B, black, allelomorphic with b, absence of black and N, white, ailelo- morphic with n, absence of white..He further postulates hypostatic red (R) homozygous in abl cattle. There are certain exceptions to the general plan of inheritance which appear in all da~a whether taken from the herd books or collected directly in the field. Roans are occasionally recorded from red x red crosses and from white >: white, and both reds and whites occasionally appear from red x white and whites from red x roan. Such anomalous results have been explained in varioths ways. Those workers who have postulated theories to account for the genm'al plan of inherit a.nce, as mentioned above, have sometimes dismissed the except.ion,s as due [,o errors in recording or in identification (Wilson, ].908; WaIther, 1913; Smith, 1925); in other cases they have offered subsidiary hypotheses to account for them. Walther (1.913) and Smith 0925) suggest that roa.ning may be lost wi~h age and so lead to wrong ideritificat.ion. Wal~her (1913) suggests thai; the factors themselves may change quantitatively. Ibsen (1933) postulates a roan modifier, rm, which is recessive and which changes roan to red in t/he homozygo~.,s condition. Other workers, a.eeepting a~ least some exceptions as valid, have attempted to frame theories to embrace the complete data (Laughlia, 1911; Lloyd Joues & Evvard, 1916; Duck, ].923; Evvard, Shearer, Lindstrom & Stair.h, 1930). All such theories are tin- satisfactory in one way or another. Az pointed o~lt by other workers, some break down statistically, some demand genotypes which do nut exist (Wright, 1917; Crew, 1925; Smith, ].925; Gowen, 1927; Ibsen, 1933). Such theories need no~ be discussed here because the new facts, given below, show beyond all reasonable de,ubt that records which cq)l)ea,r 156 Inheritance of coat colour in dairy shorthorn cattle to be exceptional a.re in fiwt exceptional, b1~t that they have a very simple explanation which brings ~hem into the general scheme of inheritance. II. N~w DATA Ia the 1)resent investigation the Duke of Westminster's Eaton Herd of Pedigree Dairy Shorthorn cattle has been studied: both in the fiek'[ and from the herd books as well as from private records and photographs. The ancestry of the existing herd w is taken back five generations. Two generations, and often a thirc[, are still in the herd and available for examination; fud&ermore, the majority of ~he recorded matings used herein are within the memory of the bailiff, Mr Pakenham HamiIton. Ever), combination of colours has been made in the matings and alI colour types have been produced, but breeders have a predilection in favour of some colours, and the numbers in these cases are over~veighted in the ~:ecorded results. Hence ~he ratios of the colours obtained iu the records have no significance. Reds and red-and-whites are here recorded as such but, for purpose of analysis, the red-and-whites are treated as reds, whi~e spotting being inherited as a separate character (Smith, 1925). Similarly, the roan-and-whites are treated as roans--to avoid confusion they are also recorded as roans~ for a small amount of white spotting on a light roan is not easy to identify with cergainty. A summary of the da~a obtained in the presen~ study is given in Table 1. The sex is not recorded, as reciprocal crosses give exactly similar results. Table 1 Roan includes roan-and-whlte. Results Red and Type of cross Red white Roan White TerMs Red x red 16 12 2~ -- 30 Red x red-and-white 16 13 45 -- 33 Red-and-white x red- and-white 2 12 25 -- 16 White • red I$ -- 27 -- 28 White x red-and-white -- --- 16 -- 16 White • white Roan x red 66 31 126 15 224 Roan x red-and-white 27 52 98 I$ 178 ]~aIl X roall 28 45 177 47 297 Roan • white -- -- 21 12 33 Tonsils 156 165 473 62 856 ++ Unexpected on any monohybrid theory of roan. Counting red-and-whites as reds and roan-and-whites as roans, the crosses examined yield the results shown in Table 2. Table 2 Resldts A Type of cross 'Red Roan White Tot~s Red x red 71 85 -- 79 White x red lJ; 43 -- 44 White x white -- -- 1 1 Roan x red 176 224 2~: 402 Roan xroan 73 177 47 297 Roan • white -- 21 12 33 Totals 321 473 62 856 :~ Unexpected on any monohybrid theory of roam w Tn 193.9. I. CHESTER Jo_~Es 157 IlI. DlscrJssm~ OF rxE GENE]~AL 8CttEI~{E OF INtIERrrA~NCE These data. correspond closely with those collected by ethel workers. Apart from the exceptions to be discussed below, they could be explained by considering red and white as a.llelomorphs. This theory, however, deman&~ the absence of red in white animals and, as many workers have realized, is unsatisfa.ctory in the light of white Shorthorn by Galloway crosses. Further, it is entirely out of halanony with the observed facts of pigment distribution. White Shorthorns are never without visible i'ed in the coat--about the ears and in the eyelashes--and microscopically the white hairs themselves all show some small amount of red pigment (unpublished data). It seems eddent, therefore, that all Shorthorns are red, as Crew (1925) suggested, and the only remaining question is whether their red is the allele of the black of black breeds, as postulated by Wright (1917), or whether red is hypostatic as postulated by Ibsen (1933). From Bogart & Ibsea's observa- tions (1937) and from o~r own (unpublished), it is ceAain that homozygous black hair contains red pigment so that black and. red cannot be allelomorphs. It seems most probable, therefore, that both black breeds and Shorthorns contain hypostatic red. The scheme of inheritance therefore which most satisfactorily meets our own observed fact~ is that put forward by Ibsen in 1933: R =red--always homozygous. N =white--causes hair of any colonr to become devoid of pigment, incompletely dominant. n = not white--leaves the hair pigmented. Thus, red = RRma, roan =RRNn, white =RRNN. For the black of Gatloways Ibsen postulates a factol' B, allelomorphic with b, which gives absence of black. Thus the feminine for the main colour types involved in the white Shorthorn x Galloway croas ~dll be: Black BBnn or Bbma "] Red bbma I White hbNN ~. with red (R) homozygous in all cases. Red roan bbNn [ Blue roan BBNn or BbNn J This scheme takes no aceount of ~he variaLions in shade of red in Shorthorns--variations which are of even wider range in cattle as a whole. The constitution of red is by no means fully understood, and the absence of a known allele presents difficulty. But that red is present seems beyond doubt and the postulate of homozygous hypos~atie red (R) meets the case, though only in the nature of a first ap]?roxhn-'~tion. Ibsen's 1933 theory of colour inLeritance was modified by Bogart & Ibsen in 1937 because they believed that they had demoJis~i'a.ted black pigment in red and white hair. Microscopic studies similar to theirs ha.re been ma~te in the course of the. present investigation and have entirely failed to reveal any black pigu'ient in either red or white hair of Shorthorns. Furthermore, results exactly similar to theirs, but, in our case certainly false, can be obtained readily by certah~ metho& of examination and this, we believe, is the explanation of their findings. We hope to publish the results of our own studies of piginentation shortly, when the question of both black and red pigment will be more fully discussed. 158 Inheritanc~ of coat colour in dairy shorthorn cattle IV. E:KOEI~TIONS" .~NALYSIS AND DISCUSSION On the theory here postulated there are eleven uaexpected result~ show~ in Table I" Red • red gave roan in 2 c~sea l~ed x red-and-white gave roan in 4 c~es Red-and-white x red-and-white gave roan in 2 cases Red x white gave red in 1 case Red x roan gave white in 1 ease l~ed-and-white x roart gave white in 1 case In view of the possibility of herd-book errors (o[ the clerical type), the eleven unexpected animals, recorded above, have been exambaed as far as possible to check the colonr.

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