Answer:
Monosomy occurs when the zygote receives only one copy of a chromosome andoverall occur far less frequently than trisomy because an entire missing autosome (nonsex chromosome) is nearly always lethal.
It is therefore interesting that trisomy 21 is the only viable autosomal trisomy, because the number of protein-coding sequences predicted for chromosome 21 is the smallest of any human chromosome, with the exception of the Y chromosome.
Explanation:
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