354 Colchicine 



the designation ot male or female remains unknown. Crossing these 

 tetraploids gives three types ol offspring, XXXX, XXXY, and XXYY. 

 About 5 males to 1 female are ol^tained. The female is tested by 

 making triploids, mating tetraploids with diploids. A female XXXX, 

 the 3» pojndation crossed to male XY, should be 1:1, male, female. 

 If the -hi population is 5 males to 1 female the constitution would be 

 XXYY. The tests showed 1:1 ratios; thus females were homogametic 

 as in Mehnidriinn. 



14.5: Aneuploids and Colchicine 



Aneuploids can be created by colchicine in two ways. One pro- 

 cedure involves direct action on dividing cells in meristems.^ The 

 other method is indirect, following specific breeding procedures after 

 polyploids have been made. Until ccjlchicine was discovered, the first 

 types were very rarely seen, particularly the diploid deficient plants, 

 2?? — 1. These were discussed on page 347. In this section ihe Ijetter- 

 known, indirect method for developing aneuploids is discussed. 



The scope has been expanded to more species because colchicine 

 has stinudated the production of tetraploids. It is well known that 

 tetraploids crossed with diploids create triploids. These in turn, 

 when crossed back to diploids, become a rich source for off-type 

 plants, those with extra chromosomes. Among the higher levels, 

 pentaploids are excellent sources for aneuploids. Propagating auto- 

 tetrajiloids regularly throws plants with somatic numbers deviating 

 from the euploid value. 



Distribution being unequal at meiosis, the chromosomes in the 

 megaspore mother cell and the pollen mother cell cause the numeric- 

 ally different types. Sometimes transmission of extra types can be 

 done through the seed parent only. In other cases the transmission 

 of certain aneuploids is known only at high levels of polvploidv. If 

 a particular morjjhology of the plant can be identified -with aneu- 

 ploidy, spontaneously 'occurring cases are usually high enough to 

 create a large reservoir of extrachromosomal types. 



Aneuploids among Datura. Zea, Nicotiana. Tyitiruin, and other 

 genera have been studied extensively and have i)een used for specific 

 genetical tests before colchicine methods came into prominence. In 

 other instances, such as Gassy pi iim.^- ^^ their isolation in large num- 

 bers began when this ready method for producing polyploids was 

 discovered. 



14.=^-!: Trisomies and tetrasomics. In 1915, A. F. Blakeslee found 

 a mutant in the cultures of Datura stramonium. This was called the 

 "Glofje nuitant" because this plant had a globose capsule distinct 

 from the usual patterns. Five years later, in 1920, John Belling 



