THE TKOBLEMS OF HEKEDITY AND THEIR SOLUTION. 573 



redistrilnition will uccur in such :i way that of the li-aiiictes j)r<)(lucod 

 b}^ such ^I^^s, on an average ihoro will ])e e(iual miinlxn-s of .1 o'ainete.s 

 and of a g-ametes. 



Consequent!}' if Acrs breed together, the ikmv .1 ganietes niav meet 

 each other in fertilization, forming a zygote ^1^1, namely, the pure ^1 

 variety again. Similarly two </ gametes may meet and form aa^ or the 

 pure (f variety again. But if an ^1 gamete meets an </, it will once 

 more form At(^ with its special character. This Aa is the hybrid or 

 "mule'' form, or, as I have elsewhere called it, the heterozygote, a« 

 distinguished fi'om A^l or (/(f the homozygotes. 



Similarlv if the two gametes of two varieties distinguished l)v char- 

 acters A and /). which can not be described in tin-ms of any com- 

 mon scale — such as, for example, the '"rost^" and "" single" combs of 

 fowls — imite in fertilization, again the character of the nude form can 

 not l)e predicted. Before the experiment is made the •'nud(^" may 

 present any form. Its character or properties can as yet l)e no more 

 predicted than could those of the compounds of unknown (diMuents 

 before the discovery of the periodic law. 



But again — if the case be Mendelian — the gametes ])orne ])y AB will 

 be either ^I's or ^'s," and the cross-bred .l/>'s breeding together will 

 form viol's, ^UTh, and BB\. Moreover, if, as in the normal Mende- 

 lian case, AB\ bear on an tiverage e(pial numbers of ^1 gametes and 

 B gametes, the munerical ratio of these resulting zygotes to each 

 other w ill be 



l.Ll :!^.l/; : 1 BB. 



We have seen that Mendel makes no prediction as to the outward 

 and \ isible characters of ^Itj, but only as to the essential constitution 

 and statistical condition of its gametes in regard to the characters A 

 and B. Ne\ertheless in a large luimber of cases the character of AB 

 is known to fall into one of three categories (omitting mosaics). 



(1) The cross-l)red may almost alw^ays resemble one of its pure par- 

 ents so closely as to be i^ractically indistinguishable from that pure 

 form, as in the case of the yellow cotyledon-color of certain varieties 

 of peas when crossed with green-cotyledoned varieties; in w Inch case 

 the parental chara»-ter, yellow, thus manifested by the cross bred is 

 called "dominant," and the parental character, green, not manifested, 

 is called recessi\(\ 



(2) The crossbred may present some condition interU'cdiate between 

 the two parental forms, in which case we may still retain the term 

 "blend" as applied to the zygote. 



Such an '* intermediate" may ])e the appariMit mean betwecMi the two 

 parental forms, or be nearer to one or other in any degree. Such a 



«ThiH conception was clearly formed by Nandin sinuiltaneously with Mendel, but 

 it was not wor]«Mt out by him and remained a mere suggestion. In one jilace also 

 Focke came very near to the same idea. (See Bibliography. ) 



