A Mendelian Experiment with Aberdeenangus and West Highland
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A MENDELIAN EXPERIMENT WITH A BEI-~DEEN- ANGUS AND WEST HIGHLAND CATTLE. Br J. A. S. WATSON, B.Sc., M.C. (With Pt;~o XII.) WItILE Mendelian mlalysis has been very successfully ;~pplied to the study of the heredity of the smaller animals and of plants, very little progress has so fi~r been made in the investigation of the mode of in- hcritmme of the char~mters of the larger and more imporLant do,ncstieatcd ~mim~ls. This t~ct ix of course sufficiently explained by the obvious (lifticnlties--the large fimmeial outlay and the extended period of time necessary to obtain experimental results. It would appear, however, theft there is no alternative to the method of tedious breeding experi- ments it" the many and important problems connected with anim~l breeding ~re to be solved. A certain mnmmt of progress has indeed been made by the study of records conIa~ined in herd- ~md stud-books, but it is certain that the results of such investigations lack the scientific conclusiveness of those of earefi~lly planned and eritienl experiments. Thus such ml apparently simple question as that of the inheritance of the red, white and roan eolours in Shorthorn cattle, on which practically unlimited statistie~l evidence is available, has been investigated by sever~l workem, and three quite distinct Mendelian interpretations have been proposed--by Wilson (1), Laughlin (2), and Wentworth (3), respectively--no one of which gives a complete and satisfimtory expla- nt~tioH of the flints. The present experiment was commenced in 1910; the object laid down was to determine the mode of' inheritance, in crosses between Aberdeen-Angus and West Highland Cattle, of the horned and polled conditions, of eolour differences, of hair characters and of differences in eonformation. The two breeds may be briefly described. The Aberdeen- Angus is black in eolour, with the exception that a small amount of' white is permissible on the underline behind the umbilicus, and on the end of the bail. It is hornless, with a relatively short, smooth coaL, and is of the early-maturing beef type--i.e, short of leg, blocky, wide, heavily fleshed and small boned. With regard to the purity, in the Mendelian 60 Mendelian Expcrhne~t with Ccettle scllsc, of the colou,' and of bhe hornless condition, it is to be noted that red eah, es a,'e occasionally bo,'n li'om ])ure b,'ed black parents even in l)he most ea,'eft, lly selected he,'ds. White ,na,'ki,lgs, beyonil ~hose per- rail)ted by the b,'eed stand~u'd also occur al~ times, ,no,'e pa,'tieularly white feet. Ho,'ns, o,' ,no,'e gene,'ally what are called "sett,'s"--s,nall, firm or loose ho,'ny excrescences--were once eo,npa,'~ively common bu~ haw ~, now been all but eli,ninated by selecti~m. The general eha,'aete,' of West H ighl~md cattle is well known. They carry large sp,'eading ho,'ns, a long and shaggy coat, and a,'e of beef type, short~ of leg ~md blocky buI~ distinctly narrower in build ~md less hc~vily tleshed than the Aberdeen-Angus. They are also characteristically lal~er in reaching maturity and less readily ti~ttened. The eolom's are many-- red, black, yellow, dtm and brindled--'teeurate classification being some- what difficult in ~ percentage of eases. In the prescn~ experiment caLl;h; ot' only two eohmrs were ineluded--viz, red and dun. Four different pedigreed Angus bulls were employed in the experi- ment, and were ma~ed to seven different pure bred West Highland cows. Apart from ~he latter, two cows, which happened to be available, were included, the result of a cross between the Char~ley (a white horned breed, with black "points") and the West, Highhmd. One t}enlale of l~lle Angus x Chartley-I:Iighhmd cross was ret;~ined fbr breeding. The in- heritance of the individual characters may now be considered. (1) COAT AND CONFORMATION. Untbrtunately no data worth presenting were obtained with ,'egard to the inheritance of these characters. Attempts we,'e made dt,,'ing the earlier part of the experiment to reduce the descriptions of the coat to ~mtttal measurements of the length and dia,ne~e,' of the hai,'s. The main difllel,lty, apart from that of sampling, w'~s that the seasonal differences wu'ied greatly as between different anim'ds--e.g, an animal which had ~ relatively heavy winter co~t might have a relatively light summer cock Again the hal,' development is influenced by causes other than heredity, notably by the "condition" or degree of t~t,mss, and pregnancy. The value of' t,hese ,neast,,'ements was therefb,'e doubtful, but frequent mad regula,' exa,nination ,night still have yiehled something of interest. The ~mtho,', howeve,', was able to see the cattle only at ,'a,'e and i,','egula,' intervals du,'ing l~lle pe,'iod of the w'u', and this line of investigation w~ of necessity given t,p. The gene,'al imp,'ession ,nade by the cattle wa.s that the first hyb,'id generation w~ inte,',nediate with ,'ega,'d to coat. J. A. S. WATSON 61 The individuals were similar in coat cliaracter, with one exception ( ~ No. 8), which was distinctly shorter haired. In F. there was certainly some tbrm of segregation, individuals being obtained which approached somewhat the Highbred type and others which were almost or perhaps quite as smooth as the average Angus (cf. P1. XII, fig'. 2). The distribu- tion, however, suggested a ratio considerably more complex than the simple monohybrid one of 1 Rough:2 Intermediate :1 Smooth. With l'eg;~rd to conformation, certain of the F., suggested rai;hev strongly, in one or other point, one of the parental ~ypes; but no statement beyond this woukl be justifiable. (2) HoaNs .m) COLOUR. Below tbllows a descriptive lisb of all the animals bred during the course of l~he experiment. 60 1toms. The existing true breeding types of cattle arc either (a) horned in both sexes, or (b) polled in both. The third possible condition, which is fbund for example in certain breeds of sheep, in which the males bear horns while the females arc hornless, is not known among living cattle, though Major (4) has described this condition in skulls fl'om the tertiary deposits in Italy. It"l Generation. SIRE ~)A~I Ref. B-ef. Breed and Itef. Breed and Date No, Sex No. description No. DeSel'|l)tiOll born Itorns Coh)ur I~elllarks le, 1 AA 1 Angus-Black- H 1 W. Highland Dec. 1911 Short Black Polled Dm'k Red, horns Horned 1,', 2 9 AA 3 ,, H, C 3 Highland x Feb. 1912 Polled Dun Charfley Reddish Dmb Horned F, 3 c? AA 3 ,. H, C 4 Highland x Apr. 1912 Polled Red Sold ~A 3 Chartley months old Reddish Dun, Hornet] F, 4 AA 1 ,, H 2 Highland Dark May, 1912 .9 Black.9 Still born Red, Horned F, 5 AA 2 ,~ H 5 Highland Jan. 1912 Polled Dun Yellow Dun, Horned Ft 6 AA 2 ,, H 6 Red Horned Dec. 1911 Polled Black F, 7 AA 2 ,, H 7 Red Itorned Jan. 1912 Polled Black I"1 8 AA 4 ,, H 9 ?* Horned Jmm, 19117 Polled 1]lack y, 9 AA 4 ,, H 9 ? ~ Horned Feb. 19127 Polled Black 1'~1 No. 8 and No. 9 were purchased its yearlings. Their deseenL from a pedigreed Angus bull and pure bred Highland cows was nnquesLionable, but their parLieular dams conld not be identified wifll certainty. The latter were probably red. 62 Mendelian Experiment with Cattle It'.. Generation. Ref. Nc~ Sh'e Dam Calved Sex 11ortm Colour F2 1 Fl 1 I"1 2 1914 Female Polled Black 1",, 6 .... 1915 Female Horned Dun 1;2 iI .... 1916 Female Polled Dun I; 2 17 .... 1917 Female Polled Silver Dun I; 2 23 .... 1918 Female Polled Bed I,'~ 2 1"1 1 1,"1 5 1914 Female Polled Black 1,'., 7 .... 1915 Female Polled Dun I,',~ 12 .... 1916 Male (east.) Polled Red I,'~ 18 .... 1917 Female Polled Dun 1,'~ 3 Fx 1 1"1 6 1914 Female Polled Black 1,',, 13 .... 1916 Male (east.) Horned Black I,',, 19 .... 1917 Femlfle Horned Red I"2 24 .... 1918 Female Polled lled 1,'., 4 1"1 1 1"1 7 1914 Male (cast.) Hardseurs Bh~ck under hair 1,'., 8 .... 1915 Male (east.) Horned Black 1,'., 14 ,, ,, 1916 Female Horned Black F., 20 ,, ,, 1917 Fenmle Polled Red 1,~ 25 ,, ,, 1918 Female Polled Black 1,'., 5 l,'l 1 1"1 8 1914 Female Polled Black 1,'., 9 .... 1915 Male (cast.) Horned Black F~ 15 .... 1916 Male (cast.) Horned Black I; 2 21 ,, ,, 1917 Female Polled Black 1,',, 22 .... 1918 Male Polled Black F., 10 l"l 1 1"1 9 1915 Female Polled Black I,'~ 16 .... 1916 Female Polled Black Note. There is some doubt about the respective dams of F2 13 and 14 and 19 and 20. It is possible that the dams are reversed in either case or both, i.e. 13 and 19 may be from 1,'j 7 and 14 and 20 fl'om 1"1 6. In the present experiment the F~ generation females were all "clean polled," i.e. without any trace of horn development. F~ No. 3, a bull calf, was sold for slaughter at three months of age, at which time no horn development had occurred. The bull F~ No. 1 (PI. XII, fig. 1) developed peculiar short stout horns, which grew at an abnormally slow rate.