What Students Need to Know about Chromosomal Abnormalities.

Chromosomes are stick-shaped structures in the middle of each cell in the body. Each cell has 46 chromosomes grouped in 23 pairs. When a chromosome is abnormal, it can cause health problems in the body. Abnormal chromosomes most often happen as a result of an error during cell division. Chromosome abnormalities often happen due to one or more of these: • Errors during dividing of sex cells (meiosis) • Errors during dividing of other cells (mitosis) • Exposure to substances that cause birth defects (teratogens) There are several different genetic syndromes caused by missing or extra chromosomes, including: • Trisomy 21 or Down syndrome • Turner syndrome • Trisomy 18 • Trisomy 13 In addition, there are many microdeletion and microduplication syndromes caused by small chromosomal changes, the most well-known of which is 22 q11.2 deletion syndrome. Chromosome abnormalities, depending on their size or location, can cause a variety of birth defects and dysmorphic facial features an