Other Intersexes 485 



is probable that the M-determiners are actually genes at one 

 locus and that the different strengths are produced by at least 

 eight genes that form a series of multiple alleles. 



Other Intersexes 



In Drosophila virilis Lebedeff has found intersexes in diploid 

 flies as the result of a single autosomal gene, ix"\ The wild-type 

 allele of this gene, Ix"^ is a gene for maleness and is located in 

 the third chromosome. It produces a male tendency which reacts 

 with a female tendency produced by gene 'F, located in the X 

 chromosome. The /a:'" gene and the F gene are assumed to be 

 equally potent, and the sex of the fly is determined by the bal- 

 ance between these genes. This balance is maintained by a set 

 of suppressors which inhibit the activity of the Ix"^ gene when 

 it is opposed by an equal dose of F genes. ♦These suppressors are 

 believed to be neutral so far as sex determination is concerned 

 and to act merely as the suppressors of sex genes. Two sup- 

 pressors have been found, both dominant genes. They are gene 

 Ss, located in the third chromosome, and gene S, whose location 

 has not been determined. 



In individuals which are genotypically F Ix"^Ix"^ the male 

 tendency of the two Ix"^ genes is so much more potent than the 

 female tendency produced by the F gene that such individuals 

 are male even if the 7a:"* suppressors are present. FF Ix"^Ix"^ flies, 

 however, are females because suppressors S^Ss SS are normally 

 also present and suppress the male tendency to such an extent 

 that the two F genes overcome the two Ix"'' genes and the indi- 

 vidual is a female. The ix^ allele is also a male-determining 

 gene but is much stronger in its action than Ix^. Because of the 

 suppressors, the Ix'"' and F genes are in a balanced condition in 

 the 2X : 2A individuals so that whether an individual is male or 

 female is determined by the number of F genes and, since one F 

 gene is in one X chromosome, therefore, by the number of X chro- 

 mosomes in the diploid individual. When the recessive ix''^ is 

 homozygous, the balance attained in the 2X : 2A system if Ix"'' 

 is present is overcome in part, and individuals with two F genes 

 are not females but sterile males. If only one F gene is present, 

 the individual is male. If a fly is FF ix"Hx"^ and has the sup- 

 pressors of the ix'"' gene, it is female. However, if the suppressors 



