jS Experimental Zoology 



At some time in the history of these germ-cells one or the other 

 of these two characters comes to dominate in each cell, so that 

 half of the cells will be G{W) and half W{G). This will be 

 true both for eggs and sperm. Chance meetings of the two 

 kinds of sperm and the two kinds of eggs will give — 



G{W) W{G) 

 G{W) W{G) 



I G{W) + 2 G{W) W{G) + I W{G) 



This is the characteristic Mendelian proportion. The first 

 term, G(PF), is a gray mouse, the so-called extracted dominant, 

 i.e. it is a mouse gray in color, which, if bred to other gray 

 extracted dominants, will produce only gray mice. This means 

 that the latent white remains in the latent condition in its 

 germ-cells, all of which are G{W). • 



The second term, G{W) W{G)^ of the proportion represents also 

 a gray mouse, since the gray, G, dominates the white, W ^ when 

 both occur in the "free" condition in the same body-cell. It 

 will be noticed that the presence of the two ''free" colors, G 

 and TF, in the cells of this type indicates that the type is the same 

 as the first hybrid formed by crossing G with W \ and it is im- 

 portant to find that when inbred this type gives exactly the 

 same results {i.e. the Mendehan proportion again) as do the 

 first hybrids, GW . By the ''free" condition I mean to imply 

 that the two characters, G and W ^ have not been brought into 

 the intimate relation to each other that is assumed to occur in 

 the germ-cells at the time when the alternating dominance and 

 latency occurs. 



The third term, 1F(G), of the proportion is the extracted reces- 

 sive. It represents a white mouse containing gray in a latent 

 condition. If inbred, these white mice produce only white 

 mice, but if crossed in certain ways the latent gray color can 

 be brought out again. 



The preceding example will suffice to show how the Men- 

 delian proportion can be accounted for on the assumption of 

 alternation of the contrasted characters in the germ-cells. 



