Final answer:
Chromosome duplications usually cause phenotypic effects via unbalanced gene dosage, which leads to an overproduction of gene products and can disrupt normal development causing various abnormalities.
Step-by-step explanation:
Chromosome Duplications and Phenotypic Effects
Chromosome duplications usually cause phenotypic effects primarily through unbalanced gene dosage. By duplicating a segment of DNA, multiple copies of genes are created, leading to an increase in the amount of gene product, which can disrupt normal cellular function and development. This disruption can manifest in various physical and mental abnormalities. Although duplication can also cause position effects, where the duplicate gene segments alter gene expression based on their new location, the direct increase in gene dosage is a more common reason for the phenotypic effects seen with duplications.
Other chromosomal aberrations also profoundly affect phenotype. For instance, deletions may lead to a genetic imbalance that can be lethal to a diploid organism. Inversions and translocations can result in chromosomal breaks that affect gene function, and in the case of translocations, the effects depend on the altered positions of the genes involved. Moreover, nondisjunction events can lead to aneuploidy, which often has serious effects on phenotype and viability.