Q13 - Bombay Phenotype and the Probability of Blood Type B in a Second Child

Lisa is the daughter of Carl with ABO blood-type B and Jane with AB type. Lisa’s blood type is O. Normally, there is no parent-child relationship between AB type and O type. Detailed examinations revealed that Lisa is a rare Bombay O type (Figure 1). The ABO blood-type is determined by the outermost antigen of sugar chains on the cell membrane of red blood cells. The gene for this antigen is located on chromosome 9. Type A has A antigen, type B has B antigen, type AB has both, and type O has neither. Since the A and B antigens bind to the sugar of H antigen, the phenotype will be O regardless of the genotype in the absence of the H antigen. A person who has a homozygous h allele with a defect in the H antigen gene (H) on chromosome 19 cannot synthesize H antigen and expresses Bombay O-type (Figure 2).

Figure 1.

Using the information and data, determine which of the statements are true or which are false.

Question reproduced from IBO 2020, Theoretical Exam 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)