No. G41] SII OUTER ARTICLES AXT) CORREST'OXDEXCE 571 



CROSS-OVER VALFES IX TIIK FRUIT-FLY, DROSO- 

 PHILA AMPELOPIIILA, WJIEX THE LINKED 

 FACTORS ENTER L\ DIFFERENT WAYS 

 The factors for l)ar. round, red and wliitc eyo. are sex-linked, 

 being located in the X-ehromosoine. as sliown in inheritance. 

 For example, when a bar-eyed male is mated to a normal female 

 all the resultinti' male offspring (Fl) are normal and all of the 

 females bar eyed, as bar is dominant ; that is, factors that occur 

 in the X or first chromosome have a " criss cross " mode of in- 

 heritance following the distribution of the X-chromosomes, there 

 being but one X-eliromosome in the males and two in tlie females. 

 The relative positions of the linear series of fadnis in the X- 

 of Drosophila have been determined 1»\ Mot naii ami 

 r (^irnegie Institution). Factors that li.^ near to- 



University of Chicago Laboratories give data i-t 

 question. Using the presence and absence hyi)ot 

 represent the factor for bar and (R) the factor fo 



