Chromosome abnormalities occur when there are defects in chromosome number or structure. They can be numerical, such as having an extra or missing chromosome, or structural, with changes to the chromosome composition. Down syndrome is a numerical abnormality caused by trisomy of chromosome 21, resulting in three copies instead of the typical two copies. This leads to developmental delays and other health issues. Other examples of chromosome abnormalities include Turner syndrome, Wolf-Hirschhorn syndrome, and Jacobsen syndrome, each caused by defects or deletions of different chromosomes. Modern technologies allow for more precise identification of chromosomal imbalances compared to earlier microscope methods. Chromosomal abnormalities can impact development and functioning depending on the genes involved in the affected chromosomes.