APPENDIX I 



Selective Advantage, that genotypic condition of a cell or individual 

 or genetic class of individuals which increases its chances, relative 

 to others, of representation in later generations of cells or individuals, 



Self-Fertilization (SELnNc), V. Fertihzation. 



Self-Propagation, Reproduction. 



Self-Sterility, self-incompatibihty. v. Incompatibihty. Sometimes in- 

 correctly deduced from mere sterility and vice versa. 



Semi-Heterotypic Division, a first division of meiosis which gives rise 

 to a Restitution Nucleus following defective pairing. Rosenberg 1927. 



Semi-Lethal Gene, v. Lethal Gene. 



Semi-Sterile, of gene heterozygotes or structural hybrids in which 

 approximately half the male and female gametes are inviable. Belling 

 1914. 



Sensitive Period, the period of development during which the action 

 of a gene is sensitive to the influence of external conditions. 



Sensitive Volume, that hypothetical volume in which the occurrence 

 of an ionization must produce a given mutation. Timofeeff-Ressovsky 

 et al. 1939 



Separation, v. Reductional Separation. 



Set of Chromosomes, v. Chromosome Set. 



Sex (Sexual Differentiation), the production by an individual or 

 group of individuals, of gametes of two types, differing in size 

 and mobihty (Eggs and Sperm) such that the one can fuse only 

 with the other. The individual or organ producing eggs is Female, 

 and that producing sperm is Male. v. also Dioecy, Incompatibihty, 

 Relative Sexuality. 



Sex Chromosome, one whose distribution to one and not to another 

 of the products of meiosis determines the difference in sex of the 

 offspring. Wilson 1906. 



Sex Determination, the process by which a spore (haploid) or egg (hap- 

 loid or diploid) comes to develop the properties of one or other sex. 

 Environmental Sex Determination, where the determining con- 

 ditions are external to the spore or egg, e.g. Bonellia. 

 Genotypic Sex Determination, where the determination is by the 



genotype of the spore or egg. 

 Haplo-diploid Sex Determination, where the male arises from a 



haploid egg and the female from a diploid, e.g. in Hymenoptera. 

 Maternal Sex Determination, where the determination is by the 



genotype of the mother, e.g. Sciara. 

 Progamic Sex Determination, where the determination is by a size 

 difference of the eggs, e.g. Dinophilus. 



Elements of Getietics 4-17 DD 



