Sex Limited Inheritance in Drosophila 



T. H. MORGAN 



Reprinted by publisher's permission from Sci- 

 ence, vol. 32, 1910, pp. 120-122. 



Perhaps no other organism has contributed quite so much to man's 

 kfiowledge of genetics as has the common fruit fly, Drosophila 

 melanogaster. T. H. Morgafi recognized the virtues of this animal 

 as a subject of genetic experiments at an early date, and began to 

 breed pure cultures shortly after the turn of the cefitury. After a 

 short period one of the most momentous occassions in the history 

 of genetics took place. A white-eyed male appeared in a pure culture, 

 and the study of genetic variation and its causes begafi. Morgarfs 

 paper discusses the experimental results of breeding tests usi?ig this 

 male and his offspring. 



Again the specter of terminology causes difficulties. What Morgan 

 refers to as ''sex limited'''' is fiozu known as sex linked. The term sex 

 limited is now restricted to characteristics that occur only in a single 

 sex. Morgan also discusses the occurrence of a ''sex factor X" and, as 

 in Bateson and Punnett, refers to the characteristic as be'mg "X" or 

 "710 X." Other authors at much the same time had de?nonstrated that 

 sex i?i the fruit fly was a consequence of imequal distributiofi of 

 chromosomes, and Morgan actually demo?istrates the prese?ice of 

 genes on the sex chromosome. At no time does he say this in his 

 paper, however. 



Two very i?nportant cofitributions are made in this paper. First 

 is the discovery of a striking variant which breeds true in successive 

 gejierations. Second is the possibility of assignment of a specific gene 

 locus to a specific chromosome. An enormous and fertile field of 

 'i7ivestigation opeiied up as a result, as we shall see i?i subseque?it 

 papers. 



In a pedigree culture of Drosoph- red-eyed sisters, produced 1,237 red- 



ila which had been running for nearly eyed offspring, (Fi), and 3 white-eyed 



a year through a considerable number males. The occurrence of these three 



of generations, a male appeared with white-eyed males (Fi) (due evidently 



white eyes. The normal flies have to further sporting) will, in the pres- 



brilliant red eyes. ent communication, be ignored. 



The white-eyed male, bred to his The Fi hybrids, inbred, produced: 



63 



