CHAPTER 13 



The Autoploids 



13.1: Autotetraploids 



Oejiothera lamarckinua. var. gigas, discovered by Hugo de Vries 

 at the beginning of the twentieth century, proved to have twice the 

 number of chromosomes found in a rehued species. After colchicine 

 became known, this classic polyploid was repeated. -o'^ Plants with 

 the doubled number of chromosomes are not considered mutants, 

 even though originally the concept of mutation advanced by de Vries 

 was in part taken from his experiences with Oenothera. Increasing 

 the number of chromosomes increases the number of genes, not the 

 kind. No one would consider as nnitations the production of diploids 

 from monoploids,3i or of triploids from hybrids between tetraploids 

 and diploids. Colchicine is not a mutagenic agent in any sense, either 

 for production of chromosomal changes or in its capacity as a poly- 

 ploidizing agent. ^^ 



Without exception, the autoploids produce fewer seed than the 

 diploid from which they originated by doubling. Great variations in 

 fertility are found from species to species, from almost total sterility 

 to values as high as 75 per cent.-"'^ In subsequent generations the 

 fertility level can be raised. Among tetraploid Melilotus alba two 

 groups of tetraploids have been isolated, high-fertility and low- 

 fertility lines.91 



Many comparisons have been made between diploids and the re- 

 lated tetraploids, on a physiological, morphological, chemical, ana- 

 tomical, ecological, as well as cytogenetic basis. The differences are 

 well known, and the original gigas features have been demonstrated 

 over and over. 



Certain problems relating to chromosomal mechanisms and fer- 

 tility have not yet been solved. Less and less agreement is found on 

 the causes for lowered fertility in the autotetraploids. Autotetraj^loids 

 from homozygous lines of maize are less fertile than the correspond- 



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