APPENDIX I 



Localization, the gcnotypic property of restriction of crossing-over and 

 chiasma formation to certain corresponding parts of all the chromo- 

 somes. It may be proccntric or proterminal according to whether 

 the Contact Points are near the centromere or near the ends. 

 Darlington 193 1. 



Locus, the position occupied by a gene in a chromosome, with regard 

 to its linear order. 



M I and Mil, Metaphase of first and second division of Meiosis. Similarly 

 A I, A II, T I and T II for Anaphase and Telophase. 



Macronucleus, v. Micronucleus. 



Macrospore, Megaspore. 



Major Genes, genes whose differences or mutations are large enough to 

 be identified by their individual effects in individuals, and wliich 

 are therefore presumed to have a large effect on the selective 

 advantage of the individuals. Cf. Polygenes. 



Male, v. Sex. 



Malthusian Parameter (of Population Increase), a measure of the 

 relative rate of increase or decrease of a population when in the 

 appropriate steady state. Fisher 1930. 



Maternal Effect, Delayed Inlieritance. 



Maternal Inheritance, v. hiheritance. 



Mating, the assortment of individuals, usually zygotes, in couples leading 

 to sexual reproduction; by extension includes self-mating. 

 Mating Continuum, an aggregate of individuals whose genes system- 

 atically recombine. 

 Illegitimate Mating, any mating normally precluded by the breeding 

 system of the organism {e.g. self-polHnation in incompatible or 

 heterostyled plants, or the crossing of species). 

 Mating Group, a group of individuals, haploid or diploid, within 

 which mating is favoured at the expense of mating outside the group, 

 by genetic or environmental conditions characteristic of the group. 



Matroclinal Inheritance, v. Inheritance. 



Maturation, the formation of gametes or spores by meiosis. 

 Maturation Divisions, Meiosis. 



Mean (arithmetic), the arithmetic average of a scries of observations, 

 or quantities. 

 Weighted Mean, a mean obtained when different classes of observa- 

 tions or quantities are given different weights in the calculation. 



402 



