l58 Arcnd. L. Hagedoorn and A. C. Hagedoorn. 



We must not be misunderstood to say, that there are only two 

 types of Hooded rats, but simply, that here at least we have shown 

 a gene, which distinguished some Hooded rats from others. 



N^s 47, 3, 46, 150, are heterozygous for this genetic factor, 

 N°s 49, 125, 263 and 260 are probably homozygous for the same, 

 or at least one of each pair, and N°s 44, 45, 50, 169, 170, 195, 196, 

 193, 194, 191, 192, 197, 198, 81, 82, 83, 85 and 54 are clearly 

 without it. 



Here we have the first indication of a gene, distinguishing par- 

 tially albino rats from others, which is not that, which by its presence 

 or absence makes the distinction between Irish and Hooded rats. We 

 will for a moment call this last gene A and the newly found one B. 



Are these two genes, a and b, independantly transmitted? For 

 this we must look to the other table. Figure 4. 



Irish male N" 6 was mated to a light hooded female, 19. As 

 neither from this mating, nor from another with a light Hooded 

 female, were there light Hooded j'oung, it must be concluded that 6 

 was pure for b, though impure for A. His formula in respect to 

 these two genes was therefore AaBB. 



6 Was mated to his daughter 64, who, because of her breeding, 

 must have been AaBb. Tims the mating of 6 x 64 becomes AeBB x AaBb. 

 This should give two classes of young only, Irish and dark Hooded, 

 as we actually find. 



204 And 200 are both Irish, they have only three young of which 

 two Irish and one, N° 217, Irish or dark Hooded. 



204 Has been bred to three other females. With 202, dark 

 Hooded from 6 and 64, he gave Irish and dark Hooded children. 

 Either 204 or 202 has therefore been homozygous for B. (251 can 

 not easily be classed.) 



201 Is another sister to whom 204 has been mated, she was also 

 Irish and impure for A, like 204, for they gave some dark Hooded 

 young. 



204 Has been mated to his daughter 215, producing only Irish 

 and solidcoloured young. This proves 215 to be homozygous for A. 

 This can be further seen from her mating to 253 which produced 

 only Irish and self-coloured young. 



When male 6 was mated to light Hooded female 7, they gave 

 Irish and dark Hooded. We now come to a mating of 60 and 74, 

 half-sibs, both from male 6 and light Hooded mothers, and therefore 

 necessarily both AaBb. They ought to give some light Hooded young. 



