92 HEREDITY AND SEX 



The actual numbers obtained in the GR by YW 

 cross are as follows. These are the figures that Dexter 

 has obtained : 



GR? GR$ GW$ YR$ YW $ 



6080 2870 36 34 2373 



The apparent discrepancy between the expected 

 and the realized ratios is due to the linkage of the factors 

 that went into the cross. For instance, the factors 

 for gray and red that went in with one chromosome are 

 linked ; likewise their allelomorphs, yellow and white. 

 As shown by the analysis, the F\ female offspring 

 will have two sex chromosomes, one of each sort - 

 one from the father, the other from the mother. But 

 the male will have but one sex chromosome derived 

 from the mother. 



If in the germ-cells of the F\ females there were 

 random assortment of the allelomorphs in the sex 

 chromosomes, the ideal ratio of 4:1:1:1:1 would, as 

 has been said, be realized. But if the red and gray 

 factors tend to remain together since they go in 

 together in the one chromosome, and the yellow and 

 white in the other chromosome tend to remain together, 

 and if the chances are about 84 to 1 that the factors 

 that enter together remain together, the realized ratio 

 of 170 : 84 : 1 : 1 : 84 will be found. 



Experiments show that, for these two factors, the 

 chances are about 84 to 1 that the factors that go in 

 together remain together; hence the departure from 

 Mendel's ratios for these two pairs of characters. We 

 may make a general statement or hypothesis that 

 covers cases like these, and in fact all cases where 



