CELL GENETICS 



three types of reproductive cycle, according to the importance of 

 the diploid or haploid phase, as follows : 



(a) Meiosis immediately follows fertilisation (" zygotic 

 reduction "). The organism is then always haploid, apart from the 

 zygote. 



(b) Fertilisation immediately follows meiosis (" gametic 



Table i 

 Variation in the Haploid and Diploid Generations 



* Most are non-sexual. 



* Subordinate phase parasitic on predominant phase. 



* Some have one mitosis in the haploid phase . 



* V, Infra. 



* Except males of those with haplo-diploid sex-differentiation [v. Ch. IX.). 



* One (female) and four (male) mitoses in the haploid phase. 



reduction "). The organism is then always diploid, apart from the 

 gametes. 



(c) A mitotic generation is intercalated after each process. 

 There is then an alternation of haploid and diploid generations. 

 The single cell from which the haploid generation is derived, follow- 

 ing meiosis in the diploid, is called a spore. The spore mother-cell 

 of the diploid plant, the sporophyte, produces haploid spores from 

 which the haploid gametophytes, known as " prothaUia " in the 



