ALLKN. — THK IIKRKDITY OF COAT COLOR IN MICE. 9:') 



The second, fourth, and fifih pairs consisted each of a pigmented and an 

 albino mouse. The only circumstance under which albinos might result 

 from these three pairs is that the spotted parent should have the albino 

 character recessive, when 50 per cent of the resulting offspring should 

 be albinos. Two of these pairs produced, in a total of 16 and 7 youn*' 

 respectively, no albino young, hence it is safe to assume that the {)ig- 

 meuted parents were in each case pure, as regards the albino character, 

 and the result falls under formula (1). In the case of pair 5, however, 

 the pigmented parent evidently did contain albinism in a recessive condi- 

 tion, and the litter of two young shows the Mendelian eijuality demanded 

 by formula (fi). The third pair consisted of two spotted mice. There 

 are here three possibilities. (1) Both parents may contain albinism 

 recessive, in which case 2.5 per cent of the young produced should be 

 albinos ; (2) only one parent or (3) neither parent may contain that 

 character, so that no albinos could occur (by formulae 5 and 3). 

 Since but two offspring were obtained, it cannot be certainly told which 

 expectation is the correct one, for at least four young are theoretically 

 necessary in order that the albino class may be actually present in the 

 proportion of 1 albino to 3 pigmented mice. Generation F4 was pro- 

 duced by seven pairs, though only six of these contributed to the record 

 given. In each of the six cases, the two parents were pigmented ani- 

 mals, so that (as in the third pair of F3) three possible unions are repre- 

 sented, lu case albinos are produced by any pigmented pair, it is 

 evident, on Mendelian principles, that both parents are producing gametes 

 with the albino character as well as those with the pigment character. 

 Four of the six pairs which form this generation are of this sort, 

 hence, both parents being heterozygotes, 25 per cent of their offspring 

 are expected to be albinos (formula 2). These four pairs produced 84 

 young, of which 19 were albinos, that is, the albino class shows a short- 

 age of but 2 individuals, or about 2 per cent. lu case of the two remain- 

 ing pairs, only pigmented young were obtained, 16 and 13 respectively. 

 Had all the four parents contained albinism recessive, there would have 

 been expected 4 and 3 albinos respectively among the offspring of the 

 two pairs. Since no albinos occurred among the totals, it is safe to 

 assume that at least one parent of each pair was pure with respect to the 

 character albinism. Possibly both parents in each case were pure in this 

 respect, but the result is the same in so far as the production of albinos 

 is concerned, for none are expected in either event. 



Generation F5 results from the interbreeding of five pairs of mice from 

 generation F^. Both animals of the first, fourth, and fifth pairs were pig- 



