158 



PHYSICAL BASIS OF HEREDITY 



though a piece of the X-chromosome (recognizable from 

 its genes that normally lie in the middle of the chromo- 

 some) had become attached to one end of the other X-chro- 

 mosome. Owing to this piece (including the region that 

 contains the normal allelomorphs of vermilion and sable) 

 the individuals give unexpected results in relation to domi- 

 nance or recessiveness of certain factors. For example, 



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Fig. 63. — Scheme showing the probable relation between the extra chromosome pieces of 

 Fig. 62. and the normal 15 chromosomes of this mutant. (After Hanse.) 



a male that contains the recessive genes for vermilion and 

 for sable, normally located, and having attached to this 

 chromosome the duplicated piece (containing the normal 

 allelomorphs of vermilion and sable) is in appearance a 

 wild-type fly, instead of being vermilion sable as it would 

 otherwise be without the piece. On the other hand, a 

 female having one such chromosome and a normal ver- 

 milion sable chromosome is in appearance not wild type 



