240 Mechanism of Mendelian Heredity 



the chromosome constitution Yg Rw, where Y and g 

 and R and w are homologous chromosomes which will 

 lie alongside each other . In the formation of sex 

 cells a reduction of these four chromosomes to two 

 takes place whereby, according to the theory of Sutton, 

 the following two types of separation can take place: 

 YR and gw, or gR and Yw. (A separation into Yg 

 and Rw is impossible since the division takes place 

 only between homologous chromosomes.) Hence there 

 will be four types of eggs, YR, gw, gR, and Yw and the 

 same four types of pollen cells. The F 2 generation 

 will produce the sixteen possible combinations in equal 

 numbers : namely, 



YRYR YRgw YRgR YRYw 



gwYR gwgw gwgR gwYw 



gRYR gRgw gRgR gRYw 



YwYR Ywgw YwgR YwYw 



Since w and g are recessives and therefore disappear 

 when in combination with their respective dominants 

 Y and R the result will be 9 YR (yellow round), 3 

 Yw (yellow wrinkled), 3 Rg (round green), and I gw 

 (green wrinkled) as Mendel actually observed and as 

 all investigators since have confirmed. 



Bateson made the discovery that these Mendelian 

 ratios 9:3:3: I did not always occur when forms 

 differing in two characters were crossed. He found 

 typical and very constant deviations from this ratio 



