198 



The Journal of Heredity 



Sex-Chromosomes Identified 



In the following species the sex- 

 chromosomes have been identified in 

 the manner indicated : 



Type A. Drosophila melanogastcr — di- 

 morphism of X and Y, and non-disjunction 

 7, 1 ; X rod-like, Y hook-shaped. 



Tvpe I. Drosophila rcplcta — dimorphism 

 of X and Y; X long V-shaped, Y only half 

 as long and rod-like." 



Type J. Drosophila obscura (Oregon) — X 

 and Y as in D. rcph^ta:' 



Type K. Drosophila affinis — as above.'' 

 Type L. Drosophila caribbea — as above.^ 

 Type M. Drosophila zvillisfoni — identified 

 by means of non-disjunction; X and Y both 

 long and V-shaped (Lancefield and Metz) f 

 also show aberrant behavior in first sper- 

 matocyte division (unpublished data). 



Sex-Chromosomes Doubtful 



In a few cases our slides show in- 

 dications of a sex-chromosome di- 

 morphism, but we have insufficient 

 m.aterial to be conclusive. These cases 

 are as follows : 



Type A. Chyviomyza amocna. Scapto- 

 viyza graminum. In both of these it is the 

 rod-like pair which appears in some figures 

 to be dimorphic ; but in other figures all of 

 the pairs appear to be symmetrical, suggest- 

 ing that the apparent dimorphism in the 

 former is accidental. 



Type C. Scaptomvza adusta. One rod- 

 like pair appears slightly dimorphic in some 

 figures, and appears to be aberrant in be- 

 havior in first spermatocytes. 



In the case of Type F no serious 

 problem is presented, for it seems 

 practically certain that the dot-like 

 chromosomes are not the sex-chromo- 

 somes and hence any one of the rod- 

 like pairs may be assumed to be the 

 sex-chromosomes. This is indicated 

 alike by cytological evidence and by 

 genetical evidence in the case of Dro- 

 sophila virilis (to be considered later). 



There remains only the species in 

 which X and Y have not been identi- 

 fied, but are known to be similar, and 

 those on which there is no evidence. 



Sex-Chromosomes Apparently Similar 

 in Male 



Type A 

 D. busckii 

 D. bromeliae 

 D. robusta 

 D. simulans 



Type E 

 D. mclanica 



Type F 

 D. virilis 



D. species? (European, resembles D. ob- 

 scura) 



Type G 

 D. funcbris 



Type M 

 D. zvillisfoni (see under first heading). 



Chromosomes of Males Not Examined, 

 or Evidence Not Satisfactory 



Type A 

 D. florae 

 D. ncbulosa 

 D. qiiinaria 

 D. saltans 



Chymomyza procncmis 

 MycodrosopJi ila dim id lata 



Type B 

 D. carlci 



Type C 

 D. caloptera* 



Type D 

 D. immigrans 



Type F 

 D. cardini 

 D. mullcri 

 D. ravisdcni 

 D. similis 

 D. tripnnctata 



Type H 

 Cladochacta ncbulosa 



Type I 



D. hvdci. 



In considering the relationships of 

 the types outlined above it is necessary 

 to take account of the sex-chromosome 

 characteristics wherever possible. This 

 necessity has recently been brought out 

 in the case of D. willistoni, which was 

 formerly included under Type A.t 

 where the sex-chromosomes of the 

 species used as a standard for the 

 type (D. melanogastcr) are rod-like. It 



* In an earlier paper'', this species (called ornatipcnnis) was erroneously said to have 

 dimorphic sex-chromosomes. 



fAt that time it was not known that zvillisfoni probably lacked the small dot-like pair, 

 for only a few figures had been examined and the absence of this pair was thought to be 

 due, possibly, to over extraction or to displacement. It will be noted that the zvillisfoni group 

 also resembles Type B, but in the latter, one V-chromosome pair is much larger than the 

 other and the types arc .separated on this account. 



