322 CHROMOSOMES IN HEREDITY: PHYSIOLOGICAL 



Table 52 

 Effects of Abnormal Chromosome Constitution on Viability 



I. In Drosophila melanogaster (Fig. 12 ; cf. Li, 1927). 



Deficiency. 



Gametes {x—i). 



Nullo-J^ and -Y sperm function 



(Kuhn, 1929) and probably 



therefore all other aberrant types. 



All eggs probably fertilised. 



Zygotes (2Ar— i). 



(i) Sections : some have no effect. 



Others are lethal to larva, 

 (ii) Haplo-7F : development 



retarded, not lethal, 

 (iii) Haplo-7/ and III : lethal in 



egg stage, 

 (iv) Haplo-^ : viable male (sterile). 



Zygotes (2Ar — 2). 



(i) Sections : homozygous 



deficiencies lethal in prelarval 

 stages (including deficiencies in 



a: of J). 



(ii) Nullo-7F: little or no develop- 

 ment, 

 (iii) Nullo-X : no development 

 (similarly nullo-77 or 777). 



Reduplication. 



{X + I). 



All types of egg and sperm capable 

 of fertilisation. 



(2^+1). 

 (i) Section : no deleterious effect. 



viability slightly 

 usually 



(ii) Triplo-IV 



reduced, 

 (iii) Triplo-77 and 777 



lethal to larva, 

 (iv) Triplo-A" : usually lethal to 



larva or pupa (" super-female"). 



{2X-\-2). 



(i) Sections : " P III " lethal to 

 larva. 



(ii) Tetra-7F : lethal to young 



larva. 

 (iii) Tetra-X, 77 or 777 : cannot 



occur. 



II. In various plant species referred to in earlier tables (for 

 deficiencies, cf. Monosomies). 



The following table summarises the effect of single-section and 

 single-chromosome differences from the normal on various stages of 

 the life cycle in certain animal and plant species. 



Gametes, x -}- 1. 



Pollen (i) Fragments : viability probably slightly reduced. 



(ii) Whole chromosomes : largely eliminated but to a 



varying extent according to the chromosome, 

 (iii) Several chromosomes : all eliminated. 

 Eggs (i) Fragments / 



(ii) Whole chromosomes \ 



Unaffected. 



