The ABO blood group assorts independently of the rhesus (Rh) blood group and both assort independently of the MN blood group. Three alleles, I^A, I^B and i, occur at the ABO locus. Two alleles, R, a dominant allele producing Rh+, and r, a recessive allele for Rh-, are found at the Rh locus, and codominant alleles M and N occur at the MN locus. Each gene is autosomal.

A man with blood types B, Rh+, and N says he could not be the father of a child with blood types O, Rh−, and MN. The mother of the child has blood types A, Rh+, and MN. Is the man correct? Explain.

Key Concepts

ABO Blood Group System

The ABO blood group system is determined by the presence of antigens on the surface of red blood cells, which are encoded by three alleles: I^A, I^B, and i. Individuals can have blood types A, B, AB, or O, depending on the combination of these alleles. Type O individuals have no A or B antigens, while AB individuals express both. Understanding this system is crucial for determining potential parentage based on the child's blood type.

Rh Factor

The Rh factor is determined by the presence of the R allele, which is dominant and results in the Rh+ phenotype, while the r allele is recessive, leading to the Rh- phenotype. A person with at least one R allele will be Rh+, while only those with two r alleles will be Rh-. This concept is essential for understanding the compatibility of blood types and the inheritance patterns of the Rh factor in offspring.

Codominance and Inheritance Patterns

Codominance occurs when two different alleles are expressed equally in the phenotype, as seen with the M and N alleles in the MN blood group system. Inheritance patterns for these alleles follow Mendelian genetics, where offspring inherit one allele from each parent. This concept is vital for analyzing the blood types of the parents and determining the possible blood types of their children, particularly in the context of the man's claim.