The family with methemoglobinemia as reported by Barcroft et al.3 

Affected males are represented by black squares, male carriers by shaded squares, and female carriers by shaded circles. Three members of the family were available for the present study (#3, #5, and #6). Cytb5r activity and phenotype are indicated for each subject. The status of the remaining family members could not be established because they were deceased at the time of study.