Crossing Over 



153 



30 crossovers 30 



Total 70 CSp 



70 c sp 

 SO C sp 

 SO cSp 



Fig. 50. Gametes resulting if a chiasma forms between c and sp in 60 

 per cent of the oocytes. Starting with 50 oocytes, 20 would have no 

 chiasma between c and sp and would therefore produce 80 noncrossover 

 gametes. Thirty oocytes would have a chiasma and would produce 60 

 crossover and 60 noncrossover gametes. Thus, 60 out of the 200 gametes 

 would be of the crossover type, and we should say that there was 30 per 

 cent crossing over. To simplify the problem, all products of meiosis are 

 treated as functional, and polar body formation is disregarded. 



