APPENDIX I 



Interference {continued) 



3. Chromatid Interference, as measured by the relations of 



chromatids exchanging partners in successive Chiasmata, i.e. whether 



complementary, reciprocal or disparate. Haldatie 1931. 

 Interphase (Interkinesis), the resting stage that may occur between the 



first and second division of mciosis. Should not be apphed to the 



resting stage in general. Lundcgard 191 5. 

 Intersex, an individual of a dioecious species in which the reproductive 



organs are partly of one sex and partly of the other. Goldschmidt 1915. 

 Invariance, the reciprocal of the Variance. 

 Inversion, the reversal of the linear sequence of the genes in a segment 



of a chromosome especially in relation to the centromere. Sturtevant 



1926. 



An inversion including the centromere (Pericentric, Muller) is 



equivalent to an Interchange of the two arms of the chromosome. 



V. Structural Change. 

 IsoCHROMOSOME, a cliromosome with two homologous arms derived 



from sister chromatids by sister reunion within a terminal centromere. 



Darlington 1940 

 IsOGAMY, I . The absence of differentiation of the gametes into male and 



female. 

 2. Absence of Heterogamy. 

 Isolating Mechanism, any agency which results in isolation. Dobzhansky 



1937- 

 Can be classified [Mtiller 1942) into: i. Bars to crossing. 2. Hybrid 



incapacity. 

 Isolation, i. The condition in which individuals of common ancestry 



are separated into two mating groups. Darwin 1859. Ol two kinds: — 

 Geographic, depending merely on position. 

 Genetic, depending merely on genotype. Darlington 1933. 



These may arise successively and occur simultaneously to give 



combined geographic and genetic, which includes ecological, 



isolation. 

 2. The condition in which chromosomes or parts of chromosomes 



of common ancestry (as in Complex Heterozygotes) arc prevented 



from undergoing effective recombination. 



Karyokinesis, Mitosis. Schleicher 1878. 

 Karyology, nuclear cytology. Trow 1895. 



Karyotype, the character of a nucleus as defined by the size, shape and 

 number of the mitotic chromosomes. 



400 



