No. 497] 



HEREDITY OF HAIR FORM 



themselves straight hair. 2 The genuine cases of straight- 

 haired parents producing wavy or curly hair in the 

 children are probably cases of imperfect dominance— or 

 heterozygotes in which the recessive type appears to 

 dominate. In all such cases the grandparentage contains 

 always one or more cases of wavy or curly hair. Cases 

 of recessive heterozygotes are not rare in the experience 

 of students of heredity. They do not invalidate the 

 general idea of Mendelian dominance. Striking cases of 

 all straight-haired offspring of straight-haired parents 

 are seen in the Bah, Bea., Bri., But., Cla., Hof., Loe., Mil., 

 Oat., Pot., Keg., Sam., Spr. and Whe. families, each of 

 four or more children. In these families there are 63 

 children altogether, and all of them have straight hair. 



A second criterion of Mendelism is found in crosses of 

 the RxDR type where a recessive is mated to a hetero- 

 zygous dominant; in this case expectation is fifty per 

 cent, of each type. Eighty matings between straight and 

 heterozygous wavy give 61 straight and 52 curved-haired 

 offspring, and 22 matings between straight and curly give 

 53 straight and 38 curved ; or altogether, 116 to 90 where 

 103 of each is expectation (Cf. Dou-B., Got., Halz., Kar., 

 MeBr. families). There is a slight excess of recessives, 

 probably due in part to a tendency to designate as 

 4 'straight" boys whose curly hair is cut short: possibly 

 to some cases of failure to dominate. 



A third criterion is found in the crosses of the 

 DR X DR type where two heterozygotes are mated to- 



laborators^re as follows: (1) Citing in males the form of the short, clipped 

 hair instead of the youthful long hair. Curly hair when cut short appears as 

 straight hair; this source of error is great in the case of the grandfathers, 

 who are frequently deceased; (2) recording a hair form from a hazy 

 recollection; a slightly wavy hair is often recalled as "straight." An 

 attempt was made to get a confirmation of all doubtful cases (i. <?., not in 

 accordance with the law) and in almost all cases in which a reply was re- 

 ceived one of the two "straight" parents of curved-haired children was 

 found actually to have curved hair. One exceptional case is that of the 

 Hil family, where three wavy haired children came from two straight haired 

 parents. The mother proliaHy lias or.rly gr-rm cells which fail to dominate. 



