Vererbung, Variation, Mutation. 451 



1193) Siirface, F. M., The fourth International genetics Conference. In: Amer. 

 Natural, Bd. 47, S. 636—640, 191Ö. 



An account of the Paria meeting in 1911. Gates. 



1 194) Emerson, K.A., The simultaneous modification of distinct Men- 

 delian factors. In: Amer. Natural., Bd. 47, S. 633—636, 1913. 



The author describes an interesting case in which two apparently indepen- 

 dent factors change simultaneously from the homozygous to the heterozygous 

 conditio!! through vvhat maj^ be called a somatic mutation. That is, the formula VV 

 (duplex for variegation in maize) becomes VS (S = self-coloured red). The nature 

 of the inheritance indicates that there are separate factors Vc and Vp for varie- 

 gation of cob and pericarp, and that these simultaneously become Sc and Sp. 

 An explanation of this condition is offered on the basis of Morgan 's hypothesis 

 to explain "linkage" of characters by their being represented by adjacent por- 

 tions of the same chromosoiüe, homologous chromosomes being twisted around 

 each other in synapsis according to the observations of Janssens. This would 

 explain not only the complete linkage of characters for cob colour and pericarp 

 colour, but also the fact of their simultaneous change from one condition to the 

 other. A cytological study of the maize is much to be desired in connection 

 with these and other questions. Gates. 



1195) Pearl, R., A contribution towards an analysis of the probleni of 

 inbreeding. In: Amer. Natural., Bd. 47, S. 577—614, 1913). 



In this paper the writer developes a general theory of inbreeding, and he 

 begins with the conception of inbreeding as a narrowing in the netv.ork of des- 

 cent owing to the mating together of individuals already related to each other 

 in some degree. The inbred individual possesses fewer different ancestors in any 

 generation than the maximum number possible, and a coefficient of inbreeding 

 (Zn) is set down as follows: In the genetic passage from the n -f- 1*^ generation 

 to the n"^ generation, or in other words the contribution of the !natings of the 

 jj _]_ ^th generation to the total amount of inbreeding involved in the production of 

 an individual, the degree of inbreeding involved will be measured by the expression 



Zn == ^ -^, where Pn + i denotes the maximum possible number of 



Pb+I 



different individuals involved in the matings of the n -f 1 generation, qn + i the 

 actual number of different individuals involved in these matings. — Thus in 

 continued brother and sister matings the amount of inbreeding in four generations 

 is 87.5^ Q. In parent and offspring breeding the amount of inbreeding in three 

 generations is 81.25°,q. The pedigrees of several horses and cattle are used to 

 illustrate in detail the manner of working out the degree of inbreeding which 

 has occurred. It is concluded that there is no automatic increase in the pro- 

 portion of homozygotes in a population following any type of inbreeding except 

 self-fertilization. Gates. 



1196) Pearl, K., On the results of inbreeding a Mendelian population: 

 a correction and extension of previous conclusions. In: Amer. Natural., 

 Bd. 48, S. 57—62, 1914. 



The present note points out an error in a previous paper by the writer 

 ("A contribution towards an analysis of the problem of inbreeding", Amer. Na- 

 tural. Bd. 47, S. 577 — 614, 1913) in which it was concluded that no increase in 

 the Proportion of homozygotes in a population follows inbreeding save under 

 conditions of 1. continued self-fertilization, 2. some form of gametic assortative 



