The abo blood type locus has been mapped on chromosome 9. a father who has type ab blood and a mother who has type o blood have a child with trisomy 9 and type a blood. using this information, can you tell in which parent the nondisjunction occurred? explain your answer.

Explanation:

Blood group is controlled by 3 allele (Ia, Ib and i). So the following results are possible

So if non-disjunction had occurred in father then his gametes would contain both Ia and Ib, which when fertilized with ovum having i allele would result in IaIbi which will have blood type AB.

Non-disjunction in female would produce ovum having 2 copies of allele i (or ovum having ii). And gametes of normal male will have Ia and Ib. So if this abnormal ovum (having ii) fertilized with male gamete having allele Ia then zygote will have genotype of Iaii which will be blood type A.

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