[Campbell Biology P.358] A father has type AB blood and the mother has type O. They have a c... | Practice Question

A father has type AB blood and the mother has type O. They have a child with trisomy 9 and type A blood. In which parent did the nondisjunction of chromosome 9 occur?

  • A: In the father
  • B: In the mother
  • C: In both parents
  • D: It cannot be determined from this information.

Explanation

The father has type AB blood genotype IAIB . The mother has type O blood genotype ii . The child has trisomy 9 and type A blood. The child's genotype must be IAii. To get this genotype, the child must have received one chromosome 9 with the IA allele from the father and two chromosome 9s, both with the i allele, from the mother. Therefore, the nondisjunction event failure of homologous chromosomes or sister chromatids to separate must have occurred during meiosis in the mother.