Question

multiple choice question
what is the cause of down syndrome and patau syndrome?

nondisjunction of autosomes
nondisjunction of sex chromosomes
crossing over of autosomes
crossing over of sex chromosomes

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Explanation:

Down syndrome (trisomy 21) and Patau syndrome (trisomy 13) are caused by an extra copy of an autosomal chromosome. This extra chromosome arises when homologous autosomes fail to separate properly during cell division, a process called nondisjunction. Crossing over is a normal genetic recombination event that does not cause these syndromes, and these conditions do not involve sex chromosomes.

Answer:

nondisjunction of autosomes