GLOSSARY syy 



Hence Heterochromatin, parts of the chromosome which stain more 

 deeply or less deeply than the rest during the prophase of mitosis. Heitz, 

 1927 et al. 



[Heterogametic], producing gametes of two kinds in regard to their properties 

 of sex determination. Wilson, 19 10. 



Heterogamy, [(i)] differentiation of male and female types of gametes ; (ii) the 

 special differentiation by which in the hybrid (Enothera species two 

 kinds of gametes of both sexes are produced, but opposite kinds function 

 in opposite sexes. Renner, 1919. 



[Heteropycnosis], precocious condensation of certain chromosomes in the 

 prophase especially of meiosis {v. Precocity). Gutherz, 1906. 



Heterozygote, a zygote derived from the union of gametes dissimilar in respect 

 of the constitution of their chromosomes or from mutation in 

 a homozygote. Bateson, 1902. Used for narrower categories of hybrid, 

 as : Mendelian, Interchange, Reduplication, Fragmentation, Transloca- 

 tion, and Deficiency Heterozygotes (v. Text). 



Complex , one whose gametes have numerous differences which 



segregate as a unit. Renner, 191 7. 



Sex (a form of complex heterozygote), a zygote of the hetero- 

 zygous sex, y. y Chromosome. D., 1932. 



Heterozygous Sex {v. Y Chromosome). 



[Homogametic Sex], the homozygous sex, q.v. Wilson, 1910. 



Homology, the similarity of structures in different organisms which they 

 owe to the common ancestry of the organisms. Owen. 



Homozygote, a zygote derived from the union of gametes identical in respect 

 of their chromosomes. Bateson, 1902. 



Homozygous Sex {v. X and Y Chromosomes). 



Hybrid (used here sensu stricto as a Functional Hybrid), a heterozygote. 

 Used for the broader categories as : 



Numerical , one whose parental gametes differed in respect of the 



number of chromosomes. D., 1931 c. 



Structural , one whose parental gametes differed in respect oi the 



structure of their chromosomes. D., 1929 c. It is Eucentric when its 

 dislocated segments have the same linear sequence with respect to the 

 centromere, Dyscentric when they are relatively inverted. D., 1936 d. 



Hyperploids, diploids with an extra piece or pieces of chromosome. Mutter, 



i93f- 



Hypoploids, diploids lacking a piece or pieces of chromosome. Mutter, 1932. 



Hysteresis, a lag in the movement at one level of integration in response to 

 stress at another level, e.g., in the adjustment of the external form of a 

 chromosome to its internal stresses during the spiralisation cycle. D., 



1935. 



Interchange, an exchange of non-homologous terminal segments of chromo- 

 somes, V. Belling, 1927 h. May be symmetrical or asymmetrical with 

 respect to the centromere. (The term " segmental interchange " is 

 used by Belling to include crossing-over [q.v.], but the two are con- 

 veniently distinguished, v. Text). 



Interference, the property by which the occurrence of one crossing-over 

 reduces the chance of occurrence of another in its neighoourhood. 

 Midler, 191 6. 



Cytological , the same property as between chiasmata. Haldane, 



1931 b. 



Chromatid , the same property with respect to the chromatids 



taking part in two successive chiasmata. Haldane, 1931 b ; Mather, 1933. 



Interkinesis {v. Interphase, Resting Stage). Grigoire, 1905. 



R.A. CyTOLOGY. 19 



