Induction — 81 — Interspecific Selection 



genotype is dependent upon all the other factors present, 

 the visible effect of a certain factor being smaller the greater 

 the number of factors acting in the same direction (Ramus- 

 son). 



Intercalary Trabant. — See Trabant. 



Interchange. — An exchange of segments between non-homo- 

 logous chromosomes. 



Interference. — The effect whereby one crossing-over lessens 

 the probability of another occurring in its vicinity. 



Interference Distance. — See under Differential and Inter- 

 ference Distances. 



Inter-genic Changes. — Mutational changes involving more 

 than one locus, e.g. inversions, deletions, translocations, dupli- 

 cations. 



Intergradation. — This occurs where "two reasonably distinct 

 units come into contact and gradually merge in the area under 

 consideration". Primary Intergradation "exists if the steep- 

 ening of the slope developed gradually and took place while 

 all the populations involved were in continuous contact". Sec- 

 ondary Intergradation "refers to cases in which the two 

 units, now connected by a steeply sloping character gradient, 

 were separated completely at one time and have now come into 

 contact again, after a number of differences have evolved" 

 (Mayr, 1942). 



Interkinesis. — See Interphase. 



Intermediate. — A heterozygote whose phenotypic characters 

 (or any specified character) are not identical with those of 

 either parent but partake of the appearance of both. 



Intermitosis. — The resting stage which often occurs between 

 two mitotic divisions; interphase. 



Interphase. — The resting phase in meiosis ; the phase between 

 the two meiotic divisions when the nucleus is at rest in the 

 sense of not dividing; intermitosis; interkinesis. 



Intersexes. — (i) Individuals intermediate between male and 

 female but not functionally hermaproditic and differing from 

 gynandromorphs in that they are not made up of a mixture 

 of male and female sectors but are truly intermediate, (ii) A 

 sexual abnormality in which the individual develops first as 

 one sex and then the other. See Gynergate, Ergatomorphic 

 Male, Dinergatandromorph, and Phenotypic Intersex. 



Interspecific Selection. — Selection which operates to im- 

 prove the competitive power of one species in relation to other 

 species, as distinct from Intraspecific Selection, q.v. 



