Transgenation — • 151 — Tube Nucleus 



Triplex. — A tetraploid zygote in which a particular dominant 

 gene is represented three times (AAAa). 



Triplicate Genes. — t Three, non-cumulative, identical, but 

 non-allelic genes. 



Triple-. — The term triplo-, folowed by a symbol designating 

 a particular chromosome, indicates an individual in whose 

 somatic cells there are three members of this particular chromo- 

 some, cf. Hapio- ; Diplo-. 



Triploid. — Having three haploid sets of chromosomes in the 

 somatic cells. 



Trisomic. — An organism with three chromosomes of one 

 type; usually otherwise diploid (2x -|- 1). A diploid organism 

 is said to be doubly trisomic, not tetrasomic, when it has the 

 two extra chromosomes of two different types (2x -}- 1 -j- 1) 



(Darlington). Secondary . A trisomic organism in 



which the extra chromosome has two identical ends. Tertiary 



. A trisomic organism in which the extra chromosome 



is made up of halves corresponding with the halves of differ- 

 ent chromosomes in the normal set (Belling; Darlington). 



Trisomy. — The state of having one, or more, chromosomes 

 present three times in the somatic cells, the other chromosomes 

 being present only twice. 



Trivalent. — An association of three chromosomes held to- 

 gether by chiasmata between the diplotene stage and metaphase 

 of the first meiotic division. 



Trophic Nucleus. — The larger of two nuclei in a cell; vege- 

 tative nucleus ; macronucleus ; trophonucleus. 



Trophochromatin. — Chromatin which governs the nutritive 

 functions of the cell. 



Trophochromidia. — Chromidia which are mainly concerned 

 with the nutritive functions of the cell. 



Trophonucleus. — The larger or 'vegetative' nucleus in cer- 

 tain Protozoa. 



Trophoplasm. — 'Vegetative' or nutritive protoplasm. Un- 

 modified cytoplasm as distinct from kinoplasm. 



Trophoplast. — Plastid, q.v. 



Tropokinesis. — Rotation of the spindle axis, usually as a 

 result of treatment with colchicine or some other aberration- 

 inducing substance. 



Tube Nucleus. — The nucleus which occurs in any growing 

 pollen tube and which does not take part in fertilization but 

 is concerned with regulating the growth and behaviour of the 

 tube. 



