Blood groups in humans are characterized by the presence of antigens (specifically, glycoproteins) on the surface of red blood cells. the abo blood group is controlled by three alleles of a single gene on chromosome 9: and b are codominant, and both are dominant to į, the mn blood group is controlled by gene l on chromosome 4. the gene has two codominant alleles, lm and l^n. rh is the most complex of the blood group types, involving at least 45 different antigens. the most clinically important antigen, d or rho, is encoded by the gene rhd. which is found on chromosome 1. individuals that are rh-positive have either one or two rhd. genes, whereas the rh-negative phenotype is caused by the absence of the rhr gene. (the antithetical allele d does not exist, however the letter "d" is used to indicate the d-negative phenotype).

four babies born on the same day were accidentally mixed up in a maternity ward. given the following blood types, can you match each baby to its correct set of parents.

blood types
baby couple
a. o, mn, rh* 1. o, mn, rh x b, n, rh¯
b. ab, mn, rh* 2. a, m, rh* x b, m, rh*
c. o, m, rh- 3. a, m, rh* x a, n, rh
d. b, n, rh 4. a mn, rh x ab, m, rh*