The children of couples in which one partner has blood type O (genotype ii) and the other partner has blood type AB (genotype IᴬIᴮ) are studied. What is the expected concordance rate for blood type of MZ twins in this study? Explain your answer.

Key Concepts

Blood Type Inheritance

Blood type is determined by the ABO gene, which has three alleles: A (Iᴬ), B (Iᴮ), and O (i). Individuals with blood type O have the genotype ii, while those with blood type AB have the genotype IᴬIᴮ. The offspring of these parents can inherit one allele from each parent, leading to potential blood types A (Iᴬi) or B (Iᴮi), but not AB or O.

Monozygotic (MZ) Twins

Monozygotic twins, or identical twins, originate from a single fertilized egg that splits into two embryos. They share 100% of their genetic material, which means they have the same genotype. In studies of traits like blood type, MZ twins are expected to have the same blood type due to their identical genetic makeup.

Concordance Rate

Concordance rate refers to the probability that both twins in a pair will exhibit the same trait or condition. In the context of blood type, if one MZ twin has a specific blood type, the concordance rate indicates the likelihood that the other twin will have the same blood type. Given the genetic inheritance patterns, MZ twins from the described parents will have a concordance rate of 100% for blood type, as they will inherit the same alleles.