x] Sex and Spurious A llelomorphism 175 



4. Lastly F^ grossulariata $ x lacticolor $ gave all the 

 $s grossulariata and all the ?s lacticolor. 



Adopting Castle's view that both sexes are heterozygous 

 in sex, Doncaster showed that a consistent scheme could 

 be devised which represented the foregoing experimental 

 results. According to this scheme the following supposi- 

 tions are made 



(1) Each sex is regarded as giving off ^-bearing 

 gametes and ^-bearing gametes. 



(2) In females heterozygous for grossulariata and lacti- 

 color there is gametic coupling such that each gamete 

 bearing the grossulariata factor bears maleness, and con- 

 versely each gamete bearing lacticolor bears femaleness 

 also. 



(3) In the heterozygous male there is no coupling. 



(4) There is selective mating between the gametes, 

 such that union can take place only between gametes of 

 opposite sex, namely such as bear maleness and femaleness 

 respectively. 



(5) Dominance attaches to the sex which is brought 

 into the zygote by the egg. 



On these assumptions the observed facts would be 

 produced. Inspection however shows that there is a sim- 

 pler and on the whole more probable solution, which avoids 

 the need for assumption (4) that selective mating occurs. 

 On this scheme two assumptions only are made. 



(1) That the female is heterozygous in sex, femaleness 

 being dominant, and the male a homozygous recessive. 



(2) That when in F^ the two dominant characters 

 femaleness and the grossulariata factor co-exist, there is 

 spurious allelomorphism or repulsion between them, such 

 that each gamete takes one or other of these factors, not 

 both. 



