A patient suffering from Down's syndrome was carefully examined. There were three 21 chromosomes in the patient. The sequence of all the genes and alleles present on two of the three 21 s t chromosomes were an exact match with the patient's mother while the third one was an exact match with the patient's father. Which of the following process was faulty to have produced this individual?

Question

A patient suffering from Down's syndrome was carefully examined. There were three 21 chromosomes in the patient. The sequence of all the genes and alleles present on two of the three 21 s t chromosomes were an exact match with the patient's mother while the third one was an exact match with the patient's father. Which of the following process was faulty to have produced this individual?, Anaphase I in maternal meiosis, Anaphase I in paternal meiosis, Anaphase II in maternal meiosis, Anaphase II in paternal meiosis

MARKS App · Accepted Answer

Down's syndrome is trisomy 21. It occurs due to non-disjunction of chromosomes during anaphase I of meiosis. Since the patient has two chromosomes from the mother, the failure of disjunction happened in anaphase I or anaphase II of maternal meiosis. Since the genes and alleles are exacty the same, the non-disjunction would have happened at anaphase II because the sister chromatids will have the same genomic content. If the non-disjunction happens at anaphase I, then the genes or alleles would not have been exactly same.

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