What is it?

Chromosomes are structures that contain the genes that encode all of the body functions and traits. Chromosomes are typically paired and each one is built from two segments (arms), separated by a centromere. There are normally 46 chromosomes, 23 pairs- one set of each pair is maternal and the other one is paternal. Sex chromosomes determine the individual’s sex- females have 2 X chromosomes (XX), whearas men have an X chromosome and a Y chromosome (XY). Chromosomal anomalies are divided into numerical anomalies, meaning the individual is missing or has an extra chromosome. An example for this kind of anomaly is trisomy 21, known as Down syndrome. Also, Turner syndrome is a condition in which a female is born with only one X chromosome. Structural anomaly means that the chromosome structure has been changed in a certain way- deletion, duplication, translocation or inversion. Most of the abnormalities occur by mistake in the egg or sperm and are present in all of the individual’s body cells. Otherwise, the mistake occurs after the conception and then only some of the body cells have it (mosaicism). The abnormality is either inherited or new- de novo. Chromosomal abnormalities occur either during mitosis or meiosis, which are stages in the cell division cycle. Risk factors for chromosomal abnormalities are advanced maternal age and some environmental factors. Abnormalities can cause many different symptoms or signs, depending on the specific cause.