BASILS OI- CHANGE 



gamete. The abnormality is not seen in respect of the larger chromo- 

 somes, whose unbalance presumably leads to too great a disturbance 

 for the fly to live. Except, that is, for the Y. An extra Y does no 

 harm and lack of the Y, as we saw, does not kill the fly, but produces 

 a male with immobile sperm. 



TABLE 8 



THE TYPES OF BALANCED AND UNBALANCED CHROMO- 

 SOME COMPLEMENTS WHERE ABCD STAND FOR A 

 SET OF FOUR 



Haploid 

 X ABCD 



Diploid ABCD 

 2x ABCD 



Triploid ABCD 



3x ABCD 



ABCD 



Autotetraploid 



4x ABCD 



ABCD 



ABCD 



ABCD 



Allotetraploid 

 4x ABCD 

 ABCD 

 A'B'C'D' 

 A'B'C'D' 



Deficient Gamete 

 X - 1 ABC - 



Monosomic Diploid 

 2x - I ABCD 

 ABC- 



Trisoniic Diploid 

 2x + 1 ABCD 

 ABCD 

 D 



Tetrasomic Diploid 

 2x + 2 ABCD 

 ABCD 



D 



D 



Doubly Trisomic Diploid 

 2x + 1 + 1 ABCD 

 ABCD 

 A--D 

 Unbalanced or Secondary 

 Polyploid ABCD 

 ABCD 

 A'B'C'D' 

 A'B'C'D' 

 A''B' 

 A"B" 



No such change of balance occurs in another whole-nucleus 

 variation, that due to the development ot an egg without fertiliza- 

 tion. Such parthenogenesis gives a haploid individual which, with 

 inbreeding and therefore nearly homozygous stocks, often develops 

 to maturity, though of reduced size. We have already seen one 

 produced artificially in a sea-urchin (Fig. 2). At meiosis in haploids 

 the chromosomes, lacking any regular partners, are scattered like the 



98 



