Scrub — 133 — Semen 



Segregation. — The separation of genes, or of chromosomes, 



of paternal and maternal origin at meiosis. See Secondary ; 



Somatic . 



Segregation, Effective. — That which gives viable gametic 

 or zygotic combinations (especially following multiple associa- 

 tion in structural hybrids) (Darlington). 



Selection. — The choosing of individuals with any specified 

 desired characters from a population, with the object of im- 

 proving or altering the average type. See Inter-specific Selec- 

 tion; Intra-Specific Selection; Intra-sexual Selection. 



Selection, Darwin's Theory of Sexual. — Darwin postu- 

 lated: (i) that under certain circumstances there would occur 

 a struggle between males for mates, and that the characters 

 giving success in such a struggle would have sexually-selective 

 value and would be perpetuated irrespective of their natural- 

 selective value in the struggle for existence; (ii) that these 

 characters would be of two main types, (a) those sub-serving 

 male display, {b) those sub-serving combat between rival 

 males. In addition Darwin's theory postulates a rudimentary 

 esthetic sense in females and a process of female choice as 

 between rival males (c/. Huxley, 1938). 



Selection, Epigamic. — Selection involving display charac- 

 ters common to both sexes (Huxley, 1938). 



Selection, Intra-sexual. — All selection involving competi- 

 tion between individuals of one sex in the struggle for re- 

 production (Huxley, 1938). 



Selective Fertilization. — A preferential fertilization in which 

 certain types of gametes are more frequently fertilized than 

 would be expected on a chance basis. 



Selective Maturation. — Modified meiosis in which chromo- 

 somes derived from one parent go to one pole and those from 

 the other parent to the other pole. 



Self-bred. — Arising from an ovule, or ovules, fertilized by 

 pollen from the same plant or from within the same clone. 



Self-compatible. — Capable of fertilizing itself. 



Self-fertilization. — The fertilization resulting from self- 

 pollination. 



Self-incompatible. — Incapable of self-fertilization. 



Self-pollination. — Pollination between the pollen and stigmas 

 of the same flower or within a clone. 



Sematic Coloration. — Coloration promoting conspicuousness 

 and used for warning or signalling purposes. 



Semen. — The sperm-containing fluid ejaculated by male ani- 

 mals during coitus. 



