Knight — 90 — Dictionary 



in nuclei of the germ-line and never in somatic nuclei. (Such 

 cases have been reported in Sciara by Metz). 

 Line Breeding. — A special form of inbreeding to one an- 

 cestor, in which the mating of animals related in a lesser 

 degree than that described as in-breeding is practiced. No hard 

 and fast line can be drawn between line-breeding and in- 

 breeding. 

 Line of Breeding. — A rather indefinite term used somewhat 

 loosely, applied to a group of individuals which have descended 

 from one individual; used more frequently and correctly with 

 reference to male lines of descent (Winters). 

 Linin. — A vague term designating one or more particular 



structural components of the nucleus. 

 Linkage. — Association of genetic factors, due to the genes 

 being in the same chromosome. See, also. Sex Linkage, Com- 

 plete Sex Linkage and Partial Sex Linkage. 

 Linkage Map. — Chromosome map; a diagram of the relative 



position of the genes in a chromosome. 

 Linkage Value. — Recombination Fraction, q.v. 

 Liquor folliculi. — An albuminous, alkaline, yellowish fluid 

 filling the space between the ovum and the epithelial cells 

 of the Graafian follicle. 

 Localization. — The limiting of chiasma formation to a 



particular portion of the paired chromosome. 

 Lock and Key Theory. — The theory, propounded by Du- 

 FOUR, that the female and the male genitalia of the same species 

 (at least in insects) are so exactly fitted to each other that 

 even slight deviations in the structure of either make copu- 

 lation physically impossible (c/. Dobzhansky, 1941). 

 Locus. — The fixed position of a gene in its chromosome. 

 Long-day Plants. — Plants whose flowering-time is hastened 

 by an increased period of daylight (normally more than 

 twelve hours). Opp. Short-day Plants. 

 Loss, Arber's Lav7 of. — See under Arber. 

 Luploidion. — A species whose individuals are sexually re- 

 productive and which is composed of segments with a common 

 origin arranged in a euploid series; the segments are mor- 

 phologically separable although similar in appearance but, 

 because of differential responses in various environmentals, 

 appear to intergrade (Camp & Gilly). 

 Luteal Hormone. — Progesterone; a sex hormone which has 



a specific action on the uterine endometrium. 

 Luteinisation. — The formation, in large amount, of corpora 

 lutea in the ovary (Mottram, 1944). 



