CHROMOSOMES OF DROSOPHILA 



Chromosome Relationships and Genetic Behavior in the Genus 



Drosophila: I. A Comparison of the Chromosomes 



of Different Species of Drosophila 



Charles W. jMetz and Mildred S. Moses 

 Canicf/ic Institution of IVasJiiiujtoti, Department of Gencties 



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THE CARRIERS OF HEREDITY IN DROSOPHILA 



Figure 1. Photographs of chromosome groups of three species of 

 Drosophila, magnified about 1,000 diameters. The heavily stained bodies 

 are the chromosomes, which in these flies are arranged in pairs with al- 

 most diagrammatic precision. These minute objects play the principal role 

 in inheritance. The figures are from ovarian cells of Drosophila virilis 

 (left), Drosopliila fiincbris (middle), and Drosophila ramsdcni (right). 

 The photographs were made from our preparations by Professor E. B. 

 Wilson and were used by him in the Croonian Lecture of 1914, but have 

 not been published heretofore. They are reproduced here with his kind 

 permission. 



OWING to the ease with which 

 many species of Drosophila may 

 be iDred in the laboratory and to 

 the fact that a wide range of chromo- 

 some groups is represented within the 

 genus, species of this group have come 

 to be used extensively for comparative 

 genetical studies. The purpose of such 

 studies is two-fold. In the first place 

 it is desired to ascertain to what extent 

 different species will give rise to similar 

 ir.utations and whether or not similar 

 mutant characters are inherited in a 

 corresponding manner in the different 

 species. In the second place it is de- 

 sired to analyze the genetic make-up 

 of the chromosomes in different spe- 

 cies by means of linkage studies, and 

 on the basis of such analyses to com- 

 pare the chromosomes of the different 

 species with respect to their genetic 

 composition. In this way it may be 

 possible to correlate the genetic struc- 

 ture, so to speak, of the chromosomes, 

 with their morphological appearance, 



and thus to learn something of the evo- 

 lution of the chromosomes. 



It is our purpose to review in the 

 present and a later paper the results 

 obtained up to the present time. 

 Since the selection of species for genet- 

 ical study has been based, to a certain 

 extent, upon their chromosomal rela- 

 tions the latter may be considered first. 

 The present paper, therefore, deals 

 with the cytological evidence, leaving 

 the genetical aspects to be considered 

 later. 



In reviewing the cytological data, all 

 of the species of Drosophila and re- 

 lated genera, whose chromosomes have 

 been studied, will be included. These, 

 of course, represent only a fraction of 

 the known species, especially in the 

 genus Drosophila. The descriptions 

 are taken in large part from the previ- 

 ous papers, but they also include a 

 considerable amount of new data. In 

 presenting the data an effort has been 

 made so to arrange them that they will 



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