94 



The Journal of Heredity 



Psychiatry, the study of diseases of 

 the mind. 



Recessive, the converse of dominant; 

 applied to one of a pair of contrasted 

 Mendelian characters which cannot ap- 

 pear in the presence of the other. 



Regression, the average variation of 

 one variable for a unit variation of a 

 correlated variable. 



Segregation, (1) as used in eugenics 

 means the policy of isolating feeble- 

 minded and other anti-social individuals 

 from the normal population into in- 

 stitutions, colonies, etc. Within these 

 the two sexes are usually (and should 

 always be) segregated from each other 

 (2) The term is also used technically in 

 genetics, rather \'aguely and with various 

 meanings, but jirimarily to refer to the 

 separation of Mcndelian factors through 

 the independent distribution of such 

 factors before or at the time of formation 

 of the gametes. 



Selection, the choice (for perpetuation 

 by reproduction) from a mixed popula- 

 tion of the individuals possessing in 

 common a certain character or a certain 

 degree of some character. Two kinds 

 of selection may be distinguished: (1) 

 natural selection, in which choice is 

 made automatically by the failure to 

 reproduce (through death or some other 

 cause) of the individuals who are not 

 "fit" to pass the tests of the environ- 

 ment (vitality, disease resistance, speed, 

 success in mating or what not) ; and (2) 

 artificial selection, in which the choice 

 is made consciously by man, as a live- 

 stock breeder. 



Sex-limited, a term applied to traits 

 which differ in the two sexes, because 

 influenced by the hormones of the re- 

 productive glands. Baldness is possi- 

 bly an example in man. 



Sex-linked, a term applied to traits 

 which are connected with sex acci- 

 dentally and not physiologically in de- 

 velo])ment. The current exjilanation is 

 that such traits happen to be in the 

 same chromosome as the determiner 

 of maleness or femaleness, as the case 

 may be. Color-blindness is the classical 

 example in man. 



Sexual selection, the conscious or un- 

 conscious preference by individuals of 

 one sex, or by that sex as a whole, for 

 indi\'iduals of the other sex who possess 

 some particular attribute or attributes 

 in a degree above or below the average 

 of their sex. If the deviation of the 

 chosen character is in the same direc- 

 tion (plus or minus) as in the chooser, 

 the mating is called assortative; if in 

 one direction independent of the char- 

 acteristics of the chooser, it is called 

 preferential. 



Soma, the body as distinguished from 

 the germ-plasm. From this point of 

 view every individual consists of only 

 two parts — germ-plasm and soma or 

 somatoplasm. 



Trait, a term used by geneticists as a 

 synon\Tn of "character." 



Unit-character, in Mendelian heredity 

 a character or alternative difTercnce of 

 any kind, which is apparently not 

 capable of subdivision in heredity, but 

 is inherited as a whole, and which is 

 capable of becoming associated in new 

 combinations with other characters. 

 The term is now going out of use, as 

 it makes for clearer thinking about 

 heredity to fix the attention on the fac- 

 tors of the germ-cells instead of on the 

 characters of the adult. 



Variation, a deviation in the size, 

 shape, or other feature of a character 

 or trait, from the mean or average of 

 that character in the species. 



\'estigial, a term applied to a char- 

 acter which at some time in the evolu- 

 tionary history of the s])ccies ]Dossessed 

 importance, or functioned fully, but 

 which has now lost its importance or its 

 original use, so that it remains a mere 

 souvenir of the past, in a degenerated 

 or rudimentary condition. Example, 

 the muscles which move a man's ears. 



Zygote, the fertilized cgg-ccll, the 

 united cell formed by the union of the 

 ovum and si)crmatozoon after fertiliza- 

 tion. 



Zymotic, caused by a microorganism. 

 A term applied to diseases. Example, 

 tuberculosis. 



