Meanings of Genetic Terms 



93 



defined as organic resemblance based 

 on descent, or tlie correlation between 

 relatives. But a better definition, based 

 on the results of genetics, looks at it 

 as a mechanism, not as an external 

 appearance. From this point of view, 

 heredity may be said to be "the per- 

 sistence of certain cell-constituents (in 

 the germ-cells) through an unending 

 number of cell-divisions." 



Heterosygote, a zygotic individual 

 which contains both rriembers of an 

 allelomorphic pair. 



Homozygote, an individual which con- 

 tains only one member of an allelo- 

 morphic pair, but contains that in 

 duplicate, having received it from both 

 parents. A homozygous individual, 

 having been formed by the union of 

 like gametes, in turn regularly produces 

 gametes of only one kind with respect 

 to any given factor, thus giving rise 

 to offspring which are, in this. regard, 

 like the parents; in other words, homo- 

 zygotes regularly "breed true." An in- 

 dividual may be a homozygote with 

 respect to one factor and a heterozygote 

 with respect to another. 



Hormones, the secretions of various 

 internal glands, which are carried in the 

 blood and have an important specific 

 influence on the growth and functioning 

 of various parts of the body. Their 

 exact nature is not yet understood. 



Inborn usually means germinal, as 

 applied to a trait. Strictly speaking, 

 however, any trait which appears in a 

 child at birth might be called inborn, 

 and some writers, particularly medical 

 men, thus refer to traits acquired in 

 prenatal life. Because of this ambiguity, 

 the word should be carefully defined 

 when used, or avoided. 



Inherent, synonymous with germinal. 



Induction, a change brought about 

 in the germ-plasm with the effect of 

 temporarily modifying the characters 

 of an individual produced from that 

 germ-plasm; but not of changing in a 

 definite and permanent way any such 

 germ-plasm and therefore any indi- 

 vidual inherited traits. 



Innate, synonymous with inborn or 

 germinal. 



Latent, a term applied to traits or 

 characters whose factors exist in the 



germ-plasm of an individual, but which 

 are not visible in his body. 



Law, in natural science means a con- 

 cise and comprehensive description of 

 an observed uniform sequence of events. 

 It is thus quite different from the law 

 of jurists, who mean a rule laid down for 

 the guidance of an intelligent being, by 

 an intelligent being having power over 

 him. 



Mendelism, a collection of laws of 

 heredity, so called after the discoverer 

 of the first of them to become known; 

 also the analytical study of heredity 

 with a view to learning the constitution 

 of the germ-cells of animals and plants. 



Mendelize, to follow Mendel's laws 

 of inheritance. 



Mores, the customs or unwritten laws 

 of a people; the conventions of society: 

 popular usage or folk- ways. 



Mutation has now two accepted mean- 

 ings: (1) a profound change in the 

 germ-plasm of an organism such as will 

 produce numerous changes in its prog- 

 eny; and (2) a discontinuous heritable 

 change in a Mendelian factor. It is 

 used in the first sense by De Vries and 

 other ' ' mutationists ' ' and in the second 

 sense by Morgan and other Mendelists ; 

 confusion has arisen from failure to 

 note the difference in usage. 



Normal Curve, a curve of distribution 

 of variations which are due to a multi- 

 plicity of independent causes acting 

 equally in both directions. 



Nucleus, a central, highly organized 

 part of every living cell, which seems to 

 play a directive role in cell-development 

 and contains, among other things, the 

 chromosomes. 



Patent, a term applied to traits which 

 are represented in the body as weU as 

 the germ- plasm of an individual. The 

 converse of "latent." 



Probability Curve, the same as normal 

 curve. Also called a Gaussian curve. 



Protoplasm, "the physical basis of 

 life" ; a chemical compound or probably 

 an emulsion of numerous compounds. 

 It contains proteins which differ slightly 

 in each species of organism. It con- 

 tains carbon, hydrogen, oxygen, nitro- 

 gen, sulphur and various salts, but is 

 so complex as to defy exhaustive 

 analysis. 



