Glossary I 325 



Linkage the association of genes as a result of their occurrence in the 

 same chromosome. 



Locus the position of a gene on a chromosome; the location of equiva- 

 lent genes (alleles) on chromosomes of homologous sets. 



Lysogenic referring to those bacteria that carry temperate phages. 



Macroevolution evolutionary events usually viewed through the perspec- 

 tive of geologic time, such as the evolution of the horse from a dog- 

 sized mammal to Equiis cahallus. 



Megaspores those spores which, in vascular plants, divide to produce 

 the female gametophytic generation. 



Meiocyte a cell, the nucleus of which divides by meiosis. 



Meiotic drive a higher probability of one allele at a locus being in- 

 cluded in the gametes than that of the others. 



Melanic black, dark brown, dark-colored. 



Mendelian population a reproductive group sharing a common gene 

 pool. 



Mesozoic the age of reptiles; beginning about 200 million years ago 

 and ending about 70 million years ago. 



Metacentric chromosome a chromosome in which the centromere is 

 about midway in its length, the arms therefore equal. 



Metalloenzyme a protein associated with a metal atom or complexes of 

 metal atoms and functioning as an enzyme. 



Microevolution evolutionary events usually viewed over a short period 

 of time, such as changes in gene frequency within a population over a 

 few generations. 



Microsome a cytoplasmic constituent, obtained upon centrifugation of 

 homogenized cells, thought to consist of ribosomes and portions of the 

 endoplasmic reticulum (now largely replaced by the latter terms). 



Migration the transfer of genetic information among populations; or the 

 dispersal and establishment of organisms beyond their place of origin; 

 or a periodic movement of individuals. 



Mimicry the superficial resemblance of one organism by another, pre- 

 sumably affecting the actions of predators. 



Mitochondria cytoplasmic organelles, filamentous or spherical, composed 

 of two membranes, the innermost of which is convoluted, that are the 

 site of many reactions of cellular respiration. 



Miocene a middle epoch of the Tertiary period, beginning about 26 

 million vears ago and ending about 11 million years ago. 



Modifier genes genes whose major obvious phenotypic effect is to modify 

 the expression of other genes. 



Morphogenesis the process leading to the development of the character- 

 istic mature form of an organism. 



Multiple allelomorph an allele occurring at a locus at which at least two 

 other alleles are known to occur. 



Multivalent an association of more than two chromosomes whose homol- 

 ogous regions are synapsed by pairs. 



