64 SEX-DETERMINATION 



OOGENESIS. Gametogenesis in the female. 



PARTHENOGENESIS. Parthetios, a virgin. The development of an egg 



without activation of a sperm. 

 PATRICULINOUS. Pater, a father. Inclining heredity toward the 



paternal side. 

 PHENOTYPE. Phainein, to appear; typos, an image, (i) The sum of 



the characters exhibited by an individual. (2) A group or class 



composed of individuals all of whose characters are alike. 

 POLAR BODY. The expelled products of the two divisions of the 



oocyte nucleus in animals. 

 POLYPLOID. Polys, many; aploos, one-fold; eidos, form. An organism 



with more than two sets of homologous chromosomes. 

 REDUCTION. The halving of the chromosome number at meiosis. 

 SEGREGATION. The separation of chromosomes of paternal and 



maternal origin at meiosis. Genetically, the separation during 



the course of a breeding experiment of the alternative allelo- 



morphic characters involved. 

 SEX-CHROMOSOMES. Chromosomcs in respect of which the sexes 



differ. 

 SPERMATOCYTE. Sperma, a seed; hytos, a cell. 

 SPERM, SPERMATOZOON. The male gamete in animals. 

 SPERMATOGENESIS. Gametogenesis in the male. 

 SYNAPSIS. Synapto, to fuse together. Chromosome pairing at 



zygotene. 

 TETRAD. Tetras, four, (i) A quartet of cells formed by meiosis in a 



mother-cell. (2) The four chromatids making up a bivalent at 



meiosis. 

 TRIPLOID. An organism having three sets of chromosomes. 

 UNIVALENT. A body at the first meiotic division corresponding with 



a single chromosome. 

 x-CHROMOSOME. A sex-chromosome of which one sex possesses 



one, the other two. 

 Y-CHROMOSOME. The sex-chromosome which is the mate of the 



single X in the heterogametic sex. 

 ZYGOTE. Zygotes, yolked. (i) The cell formed by the union of the 



gametes in the fertilized egg. (2) The individual derived 



therefrom. 

 ZYGOTENE. Zygoti, yolk; taenia, a thread. The pairing threads and 



the stage at which they occur in the prophase of meiosis. 



