CHAPTER XII 

 HETEROPLOIDS 



IRREGULARITIES in the division or the separa- 

 tion of the chromosomes occasionally cause a single 

 chromosome to be added to the group. Conversely, 

 one may be lost from the group. In so far as the addition 

 of one or more chromosomes to, or loss from, a given 

 group produces a new number, the word heteroploid has 

 been used. Another word, trisomic, has also been used 

 for cases where three of one kind are present (in contrast 

 to triploid, where there are three of each kind present) 

 and the word triplo combined with the name of the par- 

 ticular chromosome in triplicate has also been used, as 

 triplo-IV in Drosophila. Still earlier, an extra chromo- 

 some was called a supernumerary or m-chromosome, etc. 

 The loss of one member of a pair is designated by the 

 term haplo- combined with the name of the particular 

 chromosome, as in the haplo-IV type in Drosophila. 



Certain mutant types of Oenothera have been found to 

 be associated with the addition of a fifteenth chromosome. 



Normally Lamarck's evening primrose has 14 chromo- 

 somes. Certain mutant types, known as lata and semi- 

 lata, have 15 chromosomes, i.e., one additional chromo- 

 some (Fig. 100). The lata plants differ from Lamarckiana 

 in many small details, although most of the differences 

 are so slight that only an expert would notice them. Ac- 

 cording to Gates, one of the lata mutants is almost com- 

 pletely male-sterile, and its production of seed is also 

 greatly reduced. In one of the semi-lata types some good 

 pollen is produced. 



