HetCTogenetic Association — 71 — Heterozygote 



Heteropolar. — Of pairing chromosomes : having the attrac- 

 tion force unevenly distributed throughout the length of the 

 chromosome (as at pachytene). 



Heteropycnosis. — Differential contraction or condensation 

 of a sex chromosome vis a vis the autosomes. This property 

 is called Negative Heteropycnosis when condensation is 

 slower in the sex chromosome than in the others and Positive 

 Heteropycnosis when the sex chromosome shows precocious 

 condensation as compared with the other chromosomes. The 

 property of heteropycnosis is not entirely limited to the sex 

 chromosomes. 



Heteropycnotic Chromosome. — A chromosome which has 

 thickened (condensed) to a greater or less extent than the re- 

 mainder of the chromosome complement. 



Heterosomes. — The sex chromosomes. See Heterochromo- 

 somes. 



Heterosis. — (i) The increased vigour often exhibited by 

 hybrid individuals, (ii) The state of being formed from the 

 union of gametes of dissimilar genetic constitution; hetero- 

 zygosis. Adj. Heterotic. 



Heterostylous. — (i) Differentiated into long- and short- 

 styled plants, (ii) Bearing two, or more, kinds of flowers 

 on the one inflorescence, generally a peripheral strap-like 

 group of neuter or male flowers and an inner group of herma- 

 phrodite flowers as in Compositae; heterostyled ; heterogam- 

 ous. 



Heterostyly. — Differentiation into long- and short-styled 

 plants. 



Heterosynapsis. — Pairing between unlike chromosomes, cf. 

 Homosynapsis. 



Heterotetraploid. — (i) Having four complete sets of chromo- 

 somes plus one or more additional chromosomes, (ii) An or- 

 ganism whose somatic nuclei are of this type. 



Heterothally. — Genetically controlled incompatibility in fungi. 



Heterotic Vigour. — Hybrid vigour. 



Heterotropic Chromosome. — A sex chromosome ; a chromo- 

 some which has no truly similar homologue in the heterozy- 

 gous sex. See W-, X- and Y-Chromosomes. 



Heterotype, or Heterotypic, Division. — The first division 

 in meiosis. 



Heterozygosis. — The state of being formed from the union 

 of gametes of dissimilar genetic constitution. 



Heterozygote. — An organism derived from the union of 

 gametes of dissimilar genetic constitution. 



