132 The Nucleus and Cytoplasm in Development 



Table 6. Methods for Production of Haploid Embryos 



TYPE OF EXPERIMENT 



PROCEDURES 



ORIGIN OF MITOTIC 

 APPARATUS ASSURING 

 NORMAL CLEAVAGE 



Parthenogenesis (activation of 



unfertilized egg by an agent 



Other than sperm) 

 Gynogenesis (development of a 



fertilized egg with maternal 



chromosomes alone) 



Gyno-merogony (development 

 of fragment of fertilized egg 

 containing egg nucleus alone) 



Androgenesis (development of 

 fertilized egg with sperm 

 nucleus alone) 



Andro-merogony (development 

 of an egg fragment with the 

 sperm nucleus alone) 



Hyper- and hypotonic solutions; punc- 

 ture with needle; high or low tem- 

 peratures; etc. 



Hybridization; radiation of sperm fluid 

 with x-rays, etc.; treatment of sperm 

 fluid with chemicals such as acri- 

 flavine, or toluidine blue; low or 

 high temperature acting during fer- 

 tilization; also occurs spontaneously 



Fragmentation of fertilized egg isolat- 

 ing egg nucleus in one half 



Radiation of egg before fertilization; 

 mechanical removal of egg nucleus; 

 low or high temperature acting dur- 

 ing fertilization; also occurs spon- 

 taneously 



Fragmentation of unfertilized egg and 

 fertilization of non-nucleated half, 

 or division of fertilized egg isolating 

 sperm nucleus in one half 



New division center (centrosome) 

 arises in egg cytoplasm 



Division 

 sperm 



center contributed by 

 is in normal fertilization 



New division center may arise in 

 cytoplasm 



Division center contributed by 

 sperm as in normal fertilization 



Same 



increase in cell number. In some glands, 

 however, almost normal size was obtained 

 either through an increase in the size of the 

 individvxal tubules, as in the lacrymal glands, 

 or through an increase in the number of 

 units, as in the thyroid. 



The fact that the most normal haploid 

 amphibian produced so far developed from 

 an egg fragment suggested that the re- 



duction of the initial amount of cytoplasm 

 and yolk, resulting in a more normal nucleo- 

 plasmic ratio at the beginning of develop- 

 ment, may have a beneficial effect. Recent 

 observations of Briggs ('49) on haploid frog 

 embryos developed from large and small eggs 

 (volume ratio 1.73 to 1) support this view. 

 Those from large eggs showed the symptoms 

 typical for anuran haploids: the heart was 



Fig. 29. Three types of haploid salamander larvae, a, Almost normal larva of Triturus pyrrhogaster, from 

 a heat-treated egg. b, Another larva of the same species, also from heat-treated egg, showing typical symp 

 toms of haploidy (stunted growth, microcephaly, edema), c. More abnormal larva of axolotl, from cold- 

 treated egg, with extreme edema and poorly developed gills. 



