SEX DETERMINATION 



linkage of the recessive gene j fu-sed (P. W. 

 Whiting, 1935a, c) . 



Snell, in 1935, presented evidence based on 

 Bostian's (1934) published data that would sup- 

 port a theory of independently segregating mul- 

 tiple sex factors. He suggested that heterozy- 

 gosity of one or more of these factors results 

 in a female, but homozygosity of all produces a 

 diploid male (Snell, 1935). 



In 1939 P. V/. Whiting proposed a theory of 

 sex determination in Habrobracon based on mul- 

 tiple alleles (P. W. Whiting, 1939). In this 

 theory, the explanation of sex inheritance in 

 close-crosses is essentially the same as that 

 proposed by P. W. Whiting in 1933. The females 

 are heterozygous for the sex factor, the haploid 

 males are of different types as regards the sex 

 factor, and the diploid males are homozygous 

 for the tv/o sex alleles involved. The impor- 

 tance of the multiple allele theory is the fact 

 that it gives an explanation of sex determina- 

 tion in outcrosses, where no diploid males are 

 produced. The upper case letters X and Y were 

 then abandoned as sex symbols, and lower case x 

 was taken to indicate the sex factor exclusive- 

 ly. The X accompanied by certain letters of 

 the alphabet now designates the various alleles 

 in the series--xa, xb, xc, etc. According to 

 the multiple allele theory any heterozygote for 

 two members of the series, xa, xb, xc, etc., is 

 female, any horaozygote or azygote (haploid) is 

 male. Given n alleles in the series, there 

 should be possible n different haploid males, n 

 corresponding diploid males and ( n2-n) /2 females . 



With respect to the three classes of off- 

 spring — females, diploid males, and haploid' 



95 



