AN EARLY FAMILY HISTORY 



OF COLOR BLINDNESS 



Illustrating the Rule That Sons Can Inherit Normal Color Vision Only from Their 

 Mothers, While Daughters May Inherit It from Either Parent or Both 



Leon J. Cole 

 Professor of Genetics, University of Wisconsin 



IN THE Philosophical Transactions 

 of the Royal Society of London for 

 1779 is recorded a rather complete 

 family history of color blindness, to 

 which, so far as I am aware, attention 

 has not been called in recent studies 

 on the subject. It consists of a letter 

 from one J. Scott, describing his own 

 condition and that of his near relatives, 

 which was communicated to the Society 

 by the Rev. Michael Lort.^ It is of 

 interest because of its early date and be- 

 cause the facts as given fall so perfectly 

 into line with the interpretation of color 

 blindness as a sex-linked character in 

 man. 



In describing the imperfection in his 

 own sight Mr. Scott states that he does 

 "not know any green in the world." 

 Pink and pale blue appeared alike ; full 

 red and full green the same. He could 

 tell yellows and all degrees of blue ex- 

 cept very pale. He was sometimes baf- 

 fled by full purple and deep blue. In 

 this connection he cites an incident 

 which is so quaint and full of human 

 interest that it may be quoted verbatim. 

 He relates : 



'T married my daughter to a genteel, 

 worthy man a few years ago ; the day 

 before the marriage he came to my 

 house, dressed in a new suit of fine 

 cloth clothes. I was much disappointed 

 that he should come (as I supposed) 

 in black: said. He should go back to 

 change his colour. But my daughter 

 said. No, no; the colour is very gen- 

 teel ; that it was my eyes that deceived 



'Papers from the Department of Genetics, Agricultural Experiment Station, University 

 of Wisconsin, No. 17. Published with the approval of the Director of the Station. 



"Lort, Michael. An account of a remarkable imperfection of sight. In a letter from 

 J. Scott to the Rev. Mr. Whiffon, of Trinity College, Cambridge. Communicated by the 



me. He was a gentleman of the law, 

 in a fine rich claret-coloured dress, 

 which is as much a black to my eyes 

 as any black that ever was dyed." 



The accompanying diagram is con- 

 structed from the data supplied by Mr. 

 Scott on the occurrence of color blind- 

 ness in his family. In the following 

 quotation the numbers inserted in 

 brackets show the position of the in- 

 dividual referred to in the diagram. To 

 use then his own words : 



"It is a family failing: my father 

 [II 1] has exactly the same impediment: 

 my mother [II 2] and one of my sis- 

 ters [III 5] were perfect in all colours: 

 my other sister [III 2] and myself 

 [III 3] alike imperfect: my last men- 

 tioned sister has two sons [IV 1, 2] 

 both imperfect: I have a son [IV 3] 

 and daughter [IV 4], who both know 

 all colours without exception ; and so 

 did their mother [HI 4] : my mother's 

 own brother [II 3] had the like impedi- 

 ment with me, though my mother, as 

 mentioned above, knew all colours very 

 well." 



Using the symbol N for normal vision 

 and n for its allelomorph, and also as- 

 suming that A'' is sex-linked, we may 

 have the following genotypes : NN, 

 homozygous normal female ; Nn, heter- 

 ozygous normal female; nn, color blind 

 female ; A'^ — , normal male ; n — . color 

 blind male. It is then possible, on the 

 basis of the data given, to designate the 

 genotypes of all the individuals men- 



Rev Michael Lort, B.D., F.R.S. ' Philos. Trans. Roy. Soc, Lond., Vol. 68 

 611-614, 1779. 



372 



Part 2, 



pp. 



