228 



The Journal of Heredity 



is cither inKil)lc to nianitcst itself at all 

 in fciuales or else does so only when 

 homozygous as in the case of horns 

 in sheep or the niahoj;any color in 

 Ayrshire cattle. 



The spot is not present in childhood, 

 hut develops at puberty. The authors 

 think it jirohable that hormones de- 

 veloping at that time may be essential. 

 'I'hev note that in one of the pedigrees 

 given bv Pearson. Xettleship. and 

 Usher, a small occipital spot was iu' 

 herited in a similar manner. 



wiirri-: spotting 



Another peculiar color character, the 

 heredity of which is easily traced, is 

 the piebald or white spotted condition. 

 In piebald individuals the skin is wholly 

 devoid of pigment in irregular areas 

 especially on the ventral surface of the 

 l.'odv, on the face and on the head. 

 There is much variation in the amount 

 of white spotting. In some families 

 there is only a white flare in hair above 

 the forehead or a small, white spot on 

 the head. Such a variation is natu- 

 rallv most conspicuous in the colored 

 races, and spotted negroes have often 

 been exhibited at shows. Simpson^ 

 and Castle studied such a case, and 

 found the piebald condition to be in- 

 herited for at least three generations 

 without a break. The trait clearly fol- 

 lowed the mechanism of a unit domi- 

 nant factor.. Pearson, Nettleship and 

 I'sher* have collected together a num- 

 ber of pedigrees involving piebalds. 

 Some of these extend for six genera- 

 tions, but in all cases, with the excep- 

 tion of the sex-limited spot already 

 noted, the trail is transmitted as a 

 dominant unit. 



An interesting family history in 

 v.hich a white flare has been trans- 

 mitted for at least six generations, and 

 probably mf)re. was published by Mil- 

 ler.' Here, as in the case of i)remature 

 gravness cited above, we lind the old 

 family tradition, so commonly foimd 

 where a peculiar trait behaves as a 

 dominant unit. In this case the white 



spot is said to have originated in a 

 posthumous son of Harry "Hotspur" 

 Percy, born in 1403. Its appearance 

 was attributed to an action of Lady 

 Percv in pressing her hands to her fore- 

 head when she swooned on hearing of 

 her husband's death at the battle of 

 Shrewsbury. 



Piebald has been spoken of as domi- 

 nant, but we do not know what a honio- 

 zvgous piebald would be like. As Castle 

 and Simpson pointed out, such an in- 

 dividual might be so nearly unpig- 

 mented that the trait would be more 

 nearlv recessive than dominant. Such 

 an individual could only come from the 

 union of piebald with piebald. Again, 

 piebald has been spoken of as a unit. 

 This is certainly true in each particular 

 familv. but it is not certain that it is 

 the same unit in each case. We might 

 get two factor ratios after a union of 

 piebald with piebald. 



ALBINISM 



Albinism is a third peculiar color 

 trait the mode of inheritance of which 

 is usually easy to understand. Pearson, 

 Nettleship. and Usher'' have collected 

 together an enormous amount of infor- 

 mation in regard to albinos, including 

 over 600 j)e(ligrees. 'I'he trait is found 

 sporadicallv among all races of the 

 world. There is much variation in the 

 degree. In the most extreme cases 

 there is exceedingly little, if any. pig- 

 ment in skin. hair, and eyes. The hair 

 is white, the skin white and very easily 

 burned by the sim. and the eyes have 

 a i)ale grav iris and a red reflection 

 through the pu])il in the proper light. 

 There is ])hotophol)ia. imperfect vision, 

 and nystagmus, all doubtless due to the 

 defective j)igmentation of the retina. 



Among l'".m'o])eans. however, no 

 >har|) line can br drawn ])etw(-'en albi- 

 nism and extreme blondness ilere the 

 phot()])hobia. imi)erfect vision, and 

 n\stagnnis are usually considered the 

 criteria. These may be combined with 

 light brown, jiale yellow, or. occasion- 

 ally, even light red hair, as well as with 



•Simpson. (J. I., and W. I-'.. Castle. .Iiiirr. Xal.. 1913. A7 .^O-hd 

 'Pearson. Xettlcshi]), and Usher, loc. cit. 

 "Miller. Newton. Joik. Hkr.. I'HS. 6:165-169. 

 "Pearson, .Nettleslii]), and Usher, lor. cil. 



