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The genetic conditions that are caused by damage, addition or loss of sex chromosomes are known as sex chromosome abnormalities. According to statistics, 1 in 400 males and 1 in 650 females show some form of sex chromosome abnormality. However, the outcome of such defects is much less pronounced when compared to autosomal defects. The four major sex chromosome abnormalities that occur in humans are listed below.
1. Klinefelters’s Syndrome
It is seen in males where they gain an extra X-chromosome and their genotype becomes XXY. The male is infertile and has small, non-functioning testicles. The affected males silence one of their X chromosomes like normal females and thus the effect of such abnormality is less pronounced.
Gynecomastia, a partial development of breasts, may be seen in some males. When the defect is more evident, other symptoms like greater stature, weak motor control, less body hair and less interest in sex are observed.
2. Turner’s Syndrome
Turner’s syndrome is seen in females. It is a condition that arises due to the absence of an X chromosome, the genotype becoming XO. The affected female is short statured, has a webbed neck, small jaws and swollen feet and hands. They do not have secondary sexual characteristics like a XX female.
They have small breasts, non-ovulating ovaries, and do not menstruate. Affected females usually have a normal intelligence level, but some may be retarded and may have some vision and hearing problems.
Refer: What is the difference between X and Y chromosomes?
3. Triple-X Syndrome
Triple-X syndrome, also known as trisomy is demonstrated by the genotype XXX. It is a relatively common occurrence in women where they gain an extra copy of the X chromosome. Affected females show physical disabilities such as incurved and little fingers (clinodactyly), wide-spaced eyes (hypertelorism), learning difficulties, early menopause and increased height. They have normal secondary sexual characertistics but may have some problem in ovarian maturation.
4. XYY Syndrome
XYY syndrome, also known as Jacob’s syndrome is a sex chromosome abnormality seen in males. The male gains an extra Y chromosome that is presented with a few symptoms. The affected males are known as super-males. They have an increased height, acne and live a normal fertile life.
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Also Read:
- Structure, Functions and Properties of Chromosomes
- Sex Determination – Boy or Girl
- Important MCQs with Solutions on Chromosomes
