APPENDIX 



LABORATORY METHODS FOR CLASS WORK ON 

 DROSOPHILA 



The fruit fly, Drosophila melanogaster, is very easy to breed in the 

 laboratory. By its use it should be possible to arrange practical work 

 for genetics classes within the time allowed in a single term. With no 

 other organism is it possible for students to obtain Fis in the time 

 available. The notes which follow will, it is hoped, give adequate 

 instructions as to the technique to use.^ 



THE ANIMAL 



Drosophila melanogaster is a cosmopolitan fly, easiest collected from 

 the neighbourhood of rotting or fermenting fruit; it is common round 

 fruit stalls, warehouses, breweries, etc. The fly is about 3 mm. in 

 length, the body colour being yellow with black bars, and the eyes red. 

 The sexes can be easily distinguished by the abdomen; in the female 

 it is pointed, while in the male it is rounded and the posterior bars 

 are fused so that the tip is solid black (Fig. 102). The development 

 from egg to adult is very rapid. At 25° C. it takes about a fortnight 

 from the deposition of eggs to the mating and egg-laying of the females 

 which hatch from them; at room temperature the period is nearer 

 three weeks. A single female lays eggs throughout a period of about 

 three weeks or more. In order to avoid overcrowding of the cultures, 

 it is best to make matings, for any particular cross, between about 

 three females and six males, and to transfer the flies to a new bottle 

 or vial every third day. 



CULTURE METHODS 



a. Containers 



The stocks of flies are best kept in half-pint milk bottles. Crosses 



and single families may be kept in flat-bottomed glass tubes or vials, 



about 4 in. by I in. in diameter. The containers are closed by wads of 



cotton-wool, which may, if desired, be enclosed in cheesecloth. When 



1 For further details see Bridges 1932c, and D.I.S. Brochures. 



