MENDELIAN SEGREGATION 21 



11). If a vestigial gray fly is mated to a long-winged 

 ebony fly, all the ofl"spring (Fi) will have long wings 

 and gray (or slightly darker) body color. If these 

 hybrids (Fi) are inbred, offspring (F2) will be pro- 

 duced in the ratios: 



9 Flies with long wings and gray body color. 

 3 Flies with vestigial wings and gray body color. 

 3 Flies with long wings and ebony body color. 

 1 Fly with vestigial wings and ebony body color. 



In the diagram (Fig. 11) the two pairs of chro- 

 mosomes that carry the genetic factors in question 

 are represented by short rods. In the vestigial fly 

 recessive factors for vestigial (v) are in the ''second" 

 chromosome. This same fly has two ''third" chro- 

 mosomes that carry only normal factors, hence a 

 pair of factors normal for ebony (E). In the ebony 

 fly the third chromosomes carry recessive factors for 

 ebony (e), while the second chromosomes carry the 

 normal factors for vestigial (V). The formulae for 

 the two parents are vvEE and Wee, and their 

 germ cells, respectively, vE and Ve. 



The Fi fly will have the composition vVEe, and 

 will show neither the vestigial nor the ebony char- 

 acter. It is heterozygous in each pair of factors — 

 i.e. one member of the second pair of chromosomes 

 carries v, the other V; similarly, for the third pair 

 of chromosomes, one member carries the factor e 

 and the other the normal allelomorph E. 



In the maturation of the germ cells of the hybrid, 

 the members of each paiT separate from each other 

 as shown in Fig. 11 in the gametogenesis of Fi. 



