18 



The Journal of Heredity 



from \-arious colors of marcs may be 

 comj^arcd to another roan Belgian 

 therein mentioned that produced about 

 half roan colts and the other half grays, 

 bays, browns, blacks and chestnuts. 

 Obviously the first horse was the more 

 prc]jotent of the two. He must have 

 transmitted red roan in every germ cell. 

 To do this, he must have been homo- 

 zygous or pure for the dominant char- 

 acters of roan pattern and bay color; 

 that is, he must have received both roan 

 and bay from sire and from dam. While 

 there is no way of exactly determining 

 what was transmitted in the germ cell, 

 the fact that both ])arcnts were bay 

 (red) roans ^ and that only bay roan 

 colts were produced would show that 

 there was onlv one chance out of ap- 

 proximately 18,062,500,000,000,000.000 

 that the assumption is wrong. 



The second horse, on the other hand, 

 was sired by a blue roan stallion out of 

 a bay marc. This indicates at once 

 that he cannot be homozygous for roan 

 since he received it from only one 

 parent, nor could he be pure for bay 

 since it came only from the dam. Yet 

 he sired about 50% of red roans and 

 blue roans, a performance which some 

 breeders might also consider prepotent. 



PREPOTENCY AND PURE BREEDING. 



This indicates the first essential of 

 prepotency, homozygosis in a dominant 

 character. Of course, the breeder be- 

 lieves that prej^otency is a property of 

 the individual and not of the character. 

 But in almost every instance the idea of 

 l)repotcncy is based on some superficial 

 and striking character like color, and 

 it is assumed that .since this character 

 a])])ears with fair unifomiity, the rest 

 of the characters must ai)pear also. As 

 a matter of fact, it is highly improbable 

 that there ever occurred ihe ideally 

 l)rei)otcnl animal described by the 

 breeder; that is, one which is able to 

 im])ress most of his characters upon his 

 l)rogeny in s])itc of the females to which 

 he is mated. The livestock man reads 

 with interest of that great line of 

 (']\(les(lale sires from Darnley down 

 Ihrovigh Topgallant, Sir i'^N'enird, the 



' There arc two cla.sses of red roans corresponding; to hays and cheslnuls, l)ul each carrying 

 the roan pattern. 



\\'hile this idea is wideh' held by 

 animal husbandmen, the man who has 

 conducted genetic experiments and 

 watched the segregation of individual 

 factors cannot help but feel that the 

 conception is manifestly outside of the 

 facts. The behavior of hereditary char- 

 acters as though controlled b\^ unit 

 factors in the germ plasm leaves no room 

 for a cumulative effect of ancestry 

 (unless the increased opportunities tc 

 bring about homozygosis through selec- 

 tion in hereditarily limited stock be 

 thus considered). 



NATURE OF THE GERM PLASM. 



Even the parent himself has no effect 

 on his progeny in an hereditary way, 

 as inheritance does not really consist in 

 the passing on of characters from one 

 generation to the next. The similar 

 characters of ])arent and progeny devel- 

 op because both parent and progeny 

 arise from qualitatively the same germ- 

 plasm (as far as the ])articular characters 

 are concerned). When one mixes lime 

 chloride and suli)huric acid he will 

 obtain lime sulphate and muriatic acid. 

 These are the end products of the 

 reaction. If he sets apart a portion of 

 the lime chloride and sulphuric acid 

 the first day and a few days later mixes 

 them, he will get the same result. The 

 results of the first day have no effect on 

 the results of the later day. When the 

 germ cell of the animal begins develop- 

 ment it corresjjonds to the first chem- 

 icals, the developed body to the end- 

 product of the reaction. Characters 

 that are alike in parent and offspring 

 arise because they come from similar 

 origin, but the body, an end-]:)roduct of 

 dcvelo])ment, no more affects the germ 

 cells that ])ro(luce the progeny, than the 

 end-])roducts of the chemical reaction 

 affected the reaction of the later day. 

 This shows by analogy how far outside 

 the facts of inheritance the conception 

 of a cumulative ancestry lies. 



To indicate the principal difference 

 between the ijrej)()tent and non-pre- 

 potent sire, the roan Belgian referred 

 to by the writer in a ])revi()us i)a])er. that 

 sired only red njan colts (256 in numbi-r) 



