198 DISTRIBUTION OF THE CHROMOSOMES 



The same series of eggs fertilized by the male- 

 producing sperm, which carries a Y chromosome, 

 would give: 



(5) (6) (7) (8) 



XY lYY . «Y YY 



O* white O" white o white dies 



If we consider these eight kinds of progeny we 

 see that the exceptional white females (7) would be 

 expected to repeat the process and be non-disjunc- 

 tional. This is what actually occurs, for all white 

 females that are the product of such a cross do, in 

 fact, give non-disjunction in the next generation. 



The red males (4) are an exceptional class but 

 should not give exceptional results when bred to any 

 normal female, nor should they transmit non-dis- 

 junction. This has been shown to be true. 



The red females are not ahke in composition, half 

 of them (1) should behave like normal females 

 heterozygous for white and the other half (2) should 

 give exceptions. There are in fact found to be 

 these two kinds of red females in equal numbers. 



The white males (5) and (6) are not alike; one 

 kind (5) is normal and the other (6) has two Y 

 chromosomes. The latter should be expected to 

 produce some XY sperm. These sperm would give 

 daughters which would not be exceptions, but such 

 females, with a formula XX Y, should produce 

 exceptions. In fact from half of the white males (5 

 and 6), daughters are produced that give non-dis- 

 junction. 



