Draw a pedigree containing two parents and four children. Both of the parents have AB blood type. The first child is type A, the second child is type AB, and the third child is type B.

The fourth child tests as having blood type O, which is not possible given the parental genotypes. Look at Figure 4.4 and read the description of the molecular process that generates ABO blood group antigens. What other mutation could account for this observation?

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. There are four main blood types: A, B, AB, and O, which result from the combination of alleles A and B. Type O individuals lack A and B antigens, while AB individuals express both. Understanding this system is crucial for analyzing inheritance patterns and potential blood type outcomes in offspring.

Inheritance Patterns

Inheritance patterns describe how genetic traits are passed from parents to offspring. In the case of blood types, both parents with AB blood type can pass on either A or B alleles, leading to possible offspring with types A, B, or AB. However, type O cannot be produced from two AB parents under normal Mendelian inheritance, indicating the need to explore other genetic factors or mutations.

Genetic Mutations

Genetic mutations are changes in the DNA sequence that can lead to variations in traits. In the context of blood types, a mutation could potentially alter the expression of blood group antigens, allowing for unexpected phenotypes like type O in the offspring of AB parents. Understanding the role of mutations is essential for explaining anomalies in genetic inheritance and phenotypic expression.