186 



THE GARDEN AND FIELD. 



September, l9l3 



ably be made that it was precisely 

 what a cock of that breed might 

 be expected to do by virtue of 

 his breed and irrespective of his 

 theoretical breeding value, but the 

 same results are reported, whether 

 the two breeds, Indian Game and 

 Plymouth Rock, were bred pure or 

 crossed or crossbreds bred toge- 

 ther. In any case it shows, as it 

 was intended to do, the depressive 

 inlluence a male can exercise on 

 the egg returns. 



— How the Theory Explains. — 



Writing last month we did so 

 assuming, from what we had 

 read, that the theory was based 

 on a simple Mendelian pair, such 

 as " rose " and " single " in combs, 



The following paragraph in the 

 Journal of the iiritish Board of 

 Agriculture, throws more light on 

 the subject : — 



" The hypothesis is that high 

 fecundity is determined by the pre- 

 sence of two unit characters (L2 

 and Li) with their corresponding 

 absences (I2 and li) ; that females 

 are Ff and males f f ; and that, 

 when L 2, I2, F and f are 'aU. pre- 

 sent in the zygote, the gametes 

 FI2 and fL2 must preponderate, 

 ence to FL2 and fl2. The allelo- 

 morphs Li and li, on the other 

 hand, form gametes in accordance 

 \vith the ordinary laws. The re- 

 sult is that hens laying qvtr thirt}- 

 eggs must all be taken as (Ff L2 

 I2 Li Li), or (Ff L2 I2 Li li), that 

 is to say, all must be heterozygous 

 for L2. It follows (as in the 

 classic case of Abraxas) that in 

 gametogenesis the combinations 

 FI2 and fl<5 must preponderate, 

 and that, consequently, the pre- 

 sence L2,^ is transmitted to sons 

 in preference to daughters." 



— The Difference. — 



Thus we have two pairs af con- 

 trasting characters, and they com- 



plicate the situation by acting on 

 different but definite lines. It would 

 appear that, in more ordinary 

 language, good laying depends on 

 the presence of two factors, ten- 

 dencies, attributes, call them either. 

 One, probably representing aver- 

 age laying, we can call Li. The 

 other representing the difference be- 

 tween that and high average lay- 

 ing, we can take to be L2. When 

 both are present the hen will be a 

 good layer, when one is present 

 she will be a, medium layer and 

 when neither are present she will 

 be a very bad layer. One is a 

 little puzzled why she should, lay 

 at all under those circumstances. 

 From our knowledge of facts, it is 

 evident that the number of egg 

 standard will vary, not only in 

 different breeds but in different 

 strains. As an illustration, if, say, 

 the average value of Li in a Hock 

 of Leghorns is 100 eggs, it mav be 

 60. eggs in Dorkings, and perhaps 

 30 in the Malay. Similarly the 

 egg value of L2 wLLL vary. Even 

 in closely bred strains we; should 

 imagine that, though the valjue of 

 say, Li, as inherited is the same, 

 there will be rather wide varia- 

 tions in actual number of eggs laid 

 even when care and feeding are the 

 sam'e for all. We don't pretend 

 to know why L2 won't pray in 

 the same yard, or rather cell, as 

 F, it is certainly ungallant, be- 

 cause in Mendelian phraseology F 

 stands for the factor femaleness, 

 so we must accept the fact and 

 merely deplore its bad taste and 

 the unnecessary trouble it puts 

 us to. In passing it may be men- 

 tioned that in up-to-date Mendel- 

 ism, sex, which the ordiinary per- 

 son would imagine as constant 

 and indivisable, is regarded with a 

 good deal of suspicion as being of 

 mixed, almost " mongrel " nature. 

 AVhat the breeder has to do, evi- 

 dently is to get his birds pure to 

 I/I, i.e., average egg production and 

 top up with L2 high ])roduction to 

 be passed on through the cocks. 



'R.oaHoro I you writ* us 



AOOiUCiD : somathmg about 

 your m«thods of breeding, rearing 

 and managing Live Stock ? Let 

 us have it if it vlli only fill the 

 baok mt a Peat card. 



As there is no apparent reason 

 why the result should not be the 

 heavy la)^er with a reasonable 

 degree of certainty instead of as a 

 more or less sporting chance as at 

 present, an}' one should be 

 glad to know how to do it. Dr. 

 Pearl, believes he can tell him how 

 but we are under no such illusions 

 — we mean, 6f course, as to our 

 own al>ility to do so — but we can 

 pass on a few explanatory cri'.imbs 

 from the Mendelian table. Just 

 here it will perhaps be as well to 

 say that we do not wish to father 

 any of our ideas, interpretations or 

 suggestions re Mendelism on to 

 anyone else — thev might not like 

 it. 



— Some Crumbs. — 



When two or more pairs of con- 

 trasting units are present, in this 

 case Li li and L2 I2 (the domin- 

 ant character is always expressed 

 in capitals, the recessive in small 

 type) each act independently of 

 each other, that is, each pair fol- 

 lows its appointed course without 

 reference to the other. Just how 

 far the following standard illus- 

 tration of these reactions will 

 hold good in this particular 

 case where sex distinction oper- 

 ates and the result is expressed in 

 product, we do not know. A strain 

 of peas is tall or dwarf, a^ horse 

 is chestnut or bay, a fowl is rose 

 or single combed, a cow is homed 

 or hornless, barley is bearded or 

 beardless, without respect to sex, 

 but, as readers may havu observed, 

 egg laving is peculiar to the fe- 

 male fowl. We could certainly 

 make ii guess Ijascd on somewhat 

 analogous but not identical cases, 

 but as readers will understand, we 



❖ 



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