Cytogenetics is an exciting, dynamic field of study which analyzes the number and structure of human and animal chromosomes. Changes that affect the number and/or structure of the chromosomes can cause problems with growth, development, and how the body functions. Chromosomal abnormalities can happen when egg and sperm cells are being made, during early fetal development, or after birth in any cell in the body. Changes to chromosome structure can disrupt genes, causing the proteins made from disrupted genes to be missing or faulty. Depending on size, location, and timing, structural changes in chromosomes can lead to birth defects, syndromes or even cancer. Alternatively, some chromosomal changes may have no effect on a person’s health.