184 Number of Chromosomes in Latliyriis 



species, than corresponds to the haploid chromosome number. Even a 

 species with but a single chromosome in the haplophase, and two in the 

 diplophase, might be allowed to contain an unlimited number of inde- 

 pendently segregating genes, as the two chromosomes in the diplophase 

 might very well be genotypically different between individuals within 

 the species. The point is, that according to the theory, there must not 

 be more independently mendlihg pairs of factors in a given biotype 

 (individual or clone) than the chromosome number of the biotype indi- 

 cates. As soon as two individuals (not to speak of more) not belonging 

 to the same biotype are introduced into the experiment, the possibility 

 of new combinations is considerably increased, unless the two original 

 individuals are homozygotic. 



An organism with only one chromosome in the haplophase (^=1) 

 will naturally only be able to have two different chromosomes at the 

 outside in the diplophase. Let us call these A and a. Two different 

 types of gamete can then arise, viz. A and a, and these can form three 

 different types of zygote: A A, Aa, and aa, of which two are homo- 

 zygotic. 



With ^= 2, a given biotype can be doubly heterozygotic ; i.e. AaBb, 

 and four kinds of gametes can be formed, viz. AB, Ah, dB and ab, of 

 which in F^ it will be possible to obtain nine diploid combinations, 

 AABB, AABb, AAbb, AaBB, AaBb, Aabb, aaBB, aaBb, and aabb, of 

 w^hich four will be homozygotic in both characters. 



Where a; = 3, 8 different gametes can be formed, giving 27 different 

 diploid combinations, of which 8 are homozygotic. 



In a word : With a given haploid chromosome number, x, we can by 

 self-fertilisation and segregation of a single individual obtain, theoretically 

 speaking, at the outside 2^ different gamete types and 3* different diploid 

 biotypes, of which 2* will be homozygotic in all characters. 



If we are to entertain any hope of controverting the theory of identity 

 between reduction division and segregation, then naturally it will be 

 necessary to work with organisms having a low chromosome number, 

 and capable of self-fertilisation. A plant with only eight chromosomes 

 (a? = 8) will on self-fertilisation be capable of forming 256 different 

 gametes, and will in F^ segregate 6561 different types. 



If the segregation experiments be commenced with more than one 

 biotype, which of course will as a rule be necessary when working with 

 species not capable of self-fertilisation, the question becomes more 

 complicated. 



Two individuals with x=l can in the diplophase differ in both 



