Trisomy for most autosomes is fatal, yet trisomy or even tetrasomy (four copies) of the x chromosome is not. what is the explanation for this difference? view available hint(s)trisomy for most autosomes is fatal, yet trisomy or even tetrasomy (four copies) of the x chromosome is not. what is the explanation for this difference? the x chromosome does not carry any genes. only one copy of the x chromosome is functional within any given cell, regardless of the total number of x chromosomes. there is a mechanism to keep only two x chromosomes functional, regardless of the total number. the number of x chromosomes is always balanced by the number of y chromosomes.