Final answer:
Sex chromosome aneuploidies have milder phenotypic effects compared to autosomal aneuploidies because of the X inactivation process, which prevents an excess in gene dosage. This allows individuals with additional X chromosomes to function normally, while autosomal aneuploidies often disrupt essential gene dosage and lead to severe or lethal conditions.
Step-by-step explanation:
Sex chromosome aneuploidies are less detrimental than autosomal aneuploidies primarily due to a mechanism called X inactivation. This process occurs early in female development, where one of the X chromosomes condenses into a dormant structure known as a Barr body. As a result, females with an extra X chromosome can still function normatively because only one X chromosome is active in each cell, preventing an overexpression of genes. In contrast, autosomal aneuploidies often lead to fatal conditions because they disrupt essential gene dosage, and such chromosomes do not have inactivation mechanisms.
Common sex chromosome aneuploidies such as Turner syndrome (X monosomy) and Klinefelter syndrome (one or more extra X chromosomes in males) exhibit milder symptoms compared to autosomal disorders like Down syndrome (trisomy 21). Although individuals with sex chromosome aneuploidies may experience certain developmental and reproductive challenges, they often live healthy lives.