102 



T. H. MORGAN 



We are concerned with the heterozygous females only. Of 

 the two sex chromosomes of these females, the one of maternal 

 origin is indicated by the heavier line in the diagram (fig. C), 

 the other, of paternal origin, is indicated by the lighter line in 

 the figm-e. In the present case there entered from the maternal 

 side the three factors: normal (red) eye (W), the second lethal 

 (I2), and normal wings (M); there entered from the paternal 

 side the three factors: white eye (w), the normal allelomorph 

 of lethal (L2), and miniature wing (m). 



In the case of this lethal the possibilities of interchange of 

 factors between these chromosomes are shown in figure C, at 

 h, c, d. If the crossing-over takes place between white and 

 lethal, the case is indicated in (b). The two gametes that re- 

 sult from this single cross-over are W L2 m and w I2 M ; the 

 latter never becomes realized in the male because he carries the 

 lethal (I2). Similarly, if the crossing over takes place between 

 lethal and miniature the two gametes that are produced are 

 W I2 m and w L2 M, of which the former carries the lethal factor. 

 There is another possibility, viz., the double crossing-over (d). 



TABLE 15a 



(From No. 4 of table 2) 



TABLE 15b 



(From No. 5 of table 2) 



