The ABO blood type locus has been mapped on chromosome 9. A father with type AB blood and a mother who has type O blood have a child with trisomy nine and type A blood. Using this information, can you tell in which parent the non-disjunction occurred? Explain your answer. (See Figures 14.11 and 15.13).

The process of failure in the separation of homologous chromosomes or sister chromosomes is known as non-disjunction. There is an occurrence of abnormal chromosomes in the offspring. It can result in certain defective or disorder conditions.

Trisomy 9 is the condition in which the occurrence of additional chromosomes in the chromosomal location is 9. It is a rare condition compared to trisomy 21 in Down syndrome. The survival rate of trisomy 9 is lower.

The child has trisomy 9 conditions that possess genotypes such as I^AI^Ai or I^Aii.The sperm produced from the father has a non-disjunction that takes place during paternal meiosis II. The non-disjunction is the process that results in the failure of the separation of chromosomes in a proper condition.

The egg having genotype ii possesses a non-disjunction condition during the process of maternal meiosis I or meiosis II.

Hence, there is a possibility that non-disjunction can take place in the father and mother.