Genotype. — The constitution of an organism with re- 

 spect to the factors of which it is made up; the sum of all the 

 genes of an organism. 



Germ-plasm. — That part of the cell-protoplasm which 

 is the material basis of heredity and is transferred from one 

 generation to another. 



Gamete. — A name for the reproductive cell, whether 

 male or female, in both animals and plants. 



Haploid. — The number of chromosomes normally 

 found in the gametes of an individual; one-half the somatic 

 or diploid number. 



Heterozygosis.- — The condition of an organism due to the 

 fact that it is a heterozygote. 



Heterozygote. — A zygote resulting from the union of 

 two gametes bearing dissimilar factors — one a dominant, 

 the other a recessive. 



Homozygote. — A zygote resulting from the union of two 

 gametes bearing similar factors, which may be either both 

 dominant, producing a dominant homozygote or both re- 

 cessive, producing a recessive homozygote. 



Hormone.- — A substance secreted or found in some or- 

 gan or tissue and carried thence in the blood to another, 

 organ or tissue which it stimulates to functional activity or 

 whose functions it inhibits. 



Hybrid. — The offspring of animals or plants of differ- 

 ent genotypes, varieties, species or genera. 



Lethal. — Destructive of Life. 



Linkage. — That type of inheritance in which the fac- 

 tors tend to remain together in the general process of segre- 

 gation; "gametic coupling" of the older terminology. 



Locus {pi. loci). — A definite point or region in a chro- 

 mosome at which is located a genetic factor or gene. 



Multiple Allelomorphs. — Factors occupying the same 

 locus of homologous chromosomes. 



Mutant. — An individual of a genotypic character dif- 

 fering from that of its parent, or those of its parents, and 

 not derived from them by a normal process of segregation or 

 by crossing-over. 



Ontogeny. — The development of the individual as op- 

 posed to phylogeny. 



Phenotype.— The sum of the externally obvious charac- 

 ters of an individual or a group of individuals. 



179 



