Final answer:
Aneuploidies cause developmental defects due to an imbalance in gene expression resulting from an abnormal number of chromosomes, such as in Down syndrome or Turner syndrome, rather than from direct gene mutations.
Step-by-step explanation:
Individuals with aneuploidies have developmental defects due to an imbalance of gene expression, not because of mutations in the genes themselves. Aneuploidies are the result of having an abnormal number of chromosomes, a condition which can arise from events such as nondisjunction during meiosis. When a cell has too many or too few chromosomes (trisomy or monosomy), this can lead to a surplus or deficiency in the products of the genes located on that chromosome. This imbalance can disrupt normal development and function, leading to various syndromes such as Down syndrome (trisomy 21) or Turner syndrome (monosomy X).
Additionally, chromosomal structural changes like deletions, duplications, inversions, and translocations can all contribute to developmental defects, depending on their size and position within the genome. For example, deletions can lead to a loss of gene function, while duplications may cause an overexpression of genes. Both scenarios can be detrimental to the organism.
in this case is that aneuploidies result in an imbalance of gene expression (Option b), which leads to developmental defects.