People are generally told that biological females have two X chromosomes while biological males have an X and a Y chromosome. However, it is just the presence or absence of a Y chromosome that researchers use to determine someone’s sex. If a person has a Y chromosome, they are considered to be a biological male and, if a person does not have a Y chromosome, they are considered a biological female. These distinctions exist because there are many sex chromosome combinations that are different from the two that are typically spoken of.
XO
Turner syndrome, sometimes represented by an XO, is a sex chromosome abnormality that leaves a female with just an X chromosome. It, like other sex chromosome abnormalities, typically occurs due to an error while the egg or sperm cell is being formed and about 1 in every 2500 female babies are born with the condition. On average females with Turner syndrome are about 4 feet, 8 inches tall. They also may not go through puberty, have menstrual periods, or functioning ovaries.
XXY
Males with Klinefelter syndrome have two X chromosomes and a Y chromosome. About 1 in 600 males has the condition but it is believed that most people are unaware that they have it. People with this sex chromosome abnormality may have fertility issues due to testicular failure. They might also be diagnosed with ADHD or autism-spectrum disorder. Because these individuals have two X chromosomes, diseases like osteoporosis or various autoimmune diseases that are common in biological females may be present. Other symptoms of Klinefelter syndrome are extra breast tissue and abnormal body proportions.
XXX
Triple X syndrome, also known as trisomy X, leaves females with three X chromosomes. It is believed that about 1 in 900 to 1,000 people have the sex chromosome abnormality; however, these numbers may be inaccurate because of a lack of obvious symptoms. Those with the condition may be taller, have wide-spaced eyes, or have the inner corners of their eye covered by vertical skin folds.
XYY
XYY syndrome is sex chromosome abnormality that leaves males with one X chromosome and two Y chromosomes. This condition is present in about 1 in 1,000 people and an individual to be very tall and have severe acne as they grow. Researchers previously believed that people with XY syndrome were more aggressive but this theory was proven to be false.
There are other survivable sex chromosome abnormalities, also called sex chromosome aneuploidies, but those are much rarer and less studied.
