Dam — 39 — Diallel Crossing 



Deletion Heterozygote. — An individual heterozygous for 

 the absence of an internal segment of one of its chromosomes. 



Deme. — Any specified assemblage of taxonomically closely 

 related individuals (Gilmour & Gregor). 



Derivative Hybrid. — A hybrid arising from a cross between 

 two hybrids. 



Desmones. — Hormones which are supposed to induce mitosis 

 (Fischer, 1945). 



Desoxycorticosterone. — A steroid, produced by the supra- 

 renal cortex which has a progesterone-like action and possibly 

 androgenic properties also. 



Desynapsis. — The falling apart of synapsing chromosomes 

 before metaphase (synapsis having first occurred during the 

 meiotic prophase). 



Detachment. — The separation of a single X-chromosome 

 from attached X-chromosomes, as a result of crossing-over 

 between the X and Y-chromosomes near the centromere. 



Determinate Variation. — Orthogenesis, q.v. 



Determiner, Determinant. — Archaic synonyms for gene. 



Deuterotoky. — Parthenogenesis in which both males and 

 females are formed. 



Deuthyalosome. — The nucleus of the immature ovum after 

 the second meiotic division. 



Deviation. — (i) A variation from the mean, (ii) An evolu- 

 tionary change arising in the middle of ontogeny. 



Deviation, Progressive. — The progressive divergence of an 

 animal, during its ontogeny, from the ontogenetic stages of 

 the ancestor. 



Deviation, Standard. — See Appendix 1. 



Devolution. — Retrogressive evolution. 



Diad. — (i) Two daughter cells arising from a spore mother- 

 cell, as a result of meiotic irregularities, instead of a tetrad, 

 (ii) An univalent chromosome (two chromatids) at meiosis. 



Diadelphous. — Having the filaments of the stamens fused 

 into two bundles, or having one stamen solitary and the re- 

 mainder fused. 



Diagenic. — Of a genetic character: passing from male to 

 male through the female by way of the sex chromosome. 



Diakinesis. — The later stages in the prophase of meiosis 

 between diplotene and prometaphase and immediately prior 

 to the dissolution of the nuclear membrane. 



Diallel Crossing. — (i) The crossing of different (inbred) 

 lines together in pairs, (ii) A method of comparing the breed- 



