n, 2n — 103 — Non-recurrent Parent 



Neoteny. — The retention of phylogenetic larval characters 



in adult life {e.g. Amphibia) ; the retention of juvenile charac- 

 ters in the adult; paedogenesis. Adj. Neotenous. 

 Net-knots. — Karyosomes. 

 Netrum. — See Initial Spindle. 

 Neurobiotaxis. — A change in the position of nerve centres 



in the brain during phylogenetic evolution due to a change in 



the nerve-fibres from which any given nerve-centre habitually 



receives its impulses. 

 Neutrophilic. — Staining readily with neutral stains. 

 New Place Effect. — The effect whereby seed from one locality 



produces different results when grown in a different locality. 

 New Reunion (of chromosomes). — Rejoining between a 



broken end and any other broken end except the one to which 



it was originally attached (Newcombe). 

 Niacin. — A component of the vitamin Bg complex. 

 Nicking. — A fortunate combination of genes which produces 



a more positive effect than the sum total of the single gene 



effects (PiNCHER, 1946). 

 Nicotinamide. — One of the components of the vitamin B2 



complex. 

 Nicotinic Acid. — CjjH^N COOH, one of the components of 



the vitamin Bg complex. 

 Nidation. — The embedding of a fertilized ovum in the uterine 



wall. 

 Nomogenesis. — The theory that the evolution of organisms 



is the result of certain processes inherent in them and that it 



follows definite laws. 

 Non-adaptive Radiation. — The evolution of several closely 



related and morphologically divergent forms without apparent 



ecological diversification (Cain, 1944). 

 Non-conjunction. — Failure of metaphase pairing. 

 Non-disjunction. — The failure of a paired chromosome to 



separate at meiosis so that both members of the pair are 



carried to the same daughter nucleus. 

 Non-homologous Pairing. — Association of non-homologous 



parts of chromosomes at pachytene; cf. Torsion Pairing (Mc- 



Clintock; Darlington). 

 Non-recurrent Parent. — Donor parent; that parent from 



which, by backcrossing, one or more genes are transferred to 



the backcross parent (recurrent parent). That parent of a 



hybrid which is not again utilized as a parent in backcrossing. 



