MEANINGS OF GENETIC TERMS 



Every New Science Coins New Words or Gives New Meanings to Others- 

 Genetics Not an Exception to Rule — Scientific Workers Forced to 

 Use Modern Terms — Explanation of Terms Should 

 Help to Avoid Confusion^ 



A CQUIRED CHARACTER, a mo- 

 /\ dification of a. germinal trait. It 

 X \. is difficult to draw a line between 

 characters that are acquired and 

 those that are inborn. The idea in- 

 volved is as follows: in a standard en- 

 vironment, a given factor in the germ- 

 plasm will develop into a trait which 

 varies not verj^ widely about a certain 

 mean. The mean of this trait is taken 

 as representing the germinal trait in its 

 typical condition. But if the environ- 

 ment be not standard, if it be consider- 

 ably changed, the trait will develop a 

 variation far from the mean of that 

 trait in the species. Thus an Ameri- 

 can, whose skin in the standard envi- 

 ronment of the United States would be 

 blonde, may under the environment of 

 Cuba develop into a brunet. Such a 

 wide variation from the mean is called 

 an acquired character ; it is usually im- 

 pressed on the organism after the ger- 

 minal trait has reached a full, typical 

 development. 



Allelomorph, one of a pair of factors 

 which are alternative to each other in 

 Mendelian inheritance. Instead of a 

 single pair, there may be a group of 

 "multiple allelomorphs," each mem- 

 ber being alternative to every other 

 member of the group. 



Allelomorphism, a relation between 

 two or more factors, such that two which 

 are present in one zygote do not both 

 enter into the same gamete, but are 

 separated into sister gametes. 



Biometry, the study of biology by 

 statistical methods. 



Brachydactyly (short-fingeredness) , a 

 condition in which the bones, particu- 



larly of the fingers and toes, fail to 

 grow to their normal length. In well- 

 marked cases one phalanx or joint is 

 wholly lacking. 



Character (a contraction of "char- 

 acteristic), a term which is used, often 

 rather vaguely, to designate any func- 

 tion, feature, or organ of the body or 

 mind. 



Chromosome (so called from its affinity 

 for certain stains), a body of peculiar 

 protoplasm, generally cylindrical in the 

 nucleus of the cell. Each species has 

 its own characteristic number, the cells 

 of the human body contain 24 chromo- 

 somes each. 



Congenital, present at birth. The 

 term fails to distinguish between traits 

 which are actually inherited, and modi- 

 fications acquired during prenatal life. 

 In the interest of clear thinking its use 

 should be avoided so far as possible. 



Correlation, a relation between two 

 variables in a certain population, such 

 as that for every variation of one, there 

 is a corresponding variation of the 

 other. Mathematically, two correlated 

 variables are thus mutually dependent. 

 But a correlation is merely a statistical 

 description of a particular case, and in 

 some other population the same two 

 variables might be correlated in a 

 different way, other influences being at 

 work on them. 



Cytology, the study of the cell, the 

 constituent unit of organisms. 



Determiner, an element or condition 

 in a germ-cell, supposed to be essential 

 to the development of a particular 

 quality, feature or manner of reaction 

 of the organisms, which arises from the 



* Although material for this glossary has been borrowed liberally from many sources, it is 

 not to be supposed that the definitions will meet with universal acceptance. It is believed, 

 however, that they will at least help those who are not familiar with the vocabulary of genetics 

 to understand what is meant when a certain word is used. — The Editor. 



91 



