Multiple Alleles in the X Chromosome 103 



Fo, the females and half the males have broad leaves, whereas 

 half the males have narrow leaves. More recently, cytological 

 observations in the species Lychnis alba which was included in 

 ^hull's L. dioica showed that an XY mechanism was present in 

 the male. 



Multiple Alleles in the X Chromosome 



Multiple alleles are found in the X chromosome as well as in 

 autosomes. In fact, one of the first series of multiple alleles to 

 3e discovered was in the sex chromosome of Drosophila melano- 

 jaster. At the locus for white, a number of alleles may be 

 found including W (red) and w^ (eosin). W is dominant to w^ 

 md to w, and w^ is dominant to w. The following types of flies 

 ?an be found: 



(TFX) (TFX)— red female (w'X) (wX)— eosin female 



(TFX) (w^X) — red female (w^X) Y — eosin male 



(WX) (wX) — red female (wX) (ivX) — white female 



(JVX) Y — red male (wX) Y — white male 

 (w^X) (w^X) — eosin female 



Various combinations can be crossed. Thus homozygous red 

 crossed with white gives red females and red males in the Fi 

 md red females, red males, and white males in the F2 in a ratio 

 )f 2:1:1. The reciprocal cross, white female by red male, 

 ^ives red females and white males in the Fi and red females, 

 vhite females, red males, and white males in equal proportions 

 n the F2. 



A red-eyed female may be heterozygous as well as homozy- 

 >'ous, and the other allele may be the gene for white or the gene 

 "or eosin. If a heterozygous red-eyed female which also has the 

 ^ene for eosin is crossed with a white-eyed male, the results are 

 •ather complicated. As can be seen from Fig. 36, the Fi consists 

 )f red females, eosin females, red males, and eosin males in 

 ^qual numbers. If all the possible matings are made between 

 he two Fi females and the two Fi males and if each cross pro- 

 luces a population of the same size, the F2 would contain a ratio 

 )f five red females, three eosin females, two red males, two eosin 

 nales, and four white males. There would be no white-eyed 

 "emales. 



