Chromosomes contain the blueprint of our genetic makeup. Click here to learn about the genetic outlook of individuals with abnormal sets of chromosomes!
Figure 1: A chromosome
Introduction
Our human body contains 23 pairs of chromosomes, of which 22 pairs are autosomal chromosomes and the last pair is sex chromosomes. The sex chromosomes determine our sex.
Human sex determination seems to be easy. In humans, there are two types of sex chromosomes called X and Y chromosomes. People who inherit two X chromosomes from their parents become female. People who inherit X and Y chromosomes from their parents become male.
However, there are still some exceptions. There are some people who were born with an extra sex chromosome or with an absent chromosome.
What causes Sex Chromosome Abnormalities?
Sex chromosome abnormalities are caused by the nondisjunction of sex chromosomes during meiosis cell division. In a normal meiosis cell division, the chromosomes of the parent cell are copied and then separated to form haploid (4) cells. However, in rare cases, the sex chromosomes fail to separate. This produces at least one cell with sex chromosome abnormalities. If this abnormal cell is fertilised, the baby will be born with a disorder in sex chromosomes.
Klinefelter syndrome (47 XXY)
This type of sex chromosome abnormality mostly occurs in males. This is caused by the nondisjunction of sex chromosomes in males. This produces a gamete with both X and Y chromosomes. If the gamete is fertilised, the man will contain XY chromosomes from his father and a Y chromosome from his mother.
Figure 2: 47,XXY
Men with Klinefelter syndrome have small testis and their breasts develop like a female. They also have fertility problems.
Turner syndrome (45 X)
Turner syndrome, a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing. During fertilisation, one of the sex cells contains an X chromosome and the other sex cell is lack of sex chromosome.
Figure 3: 45X
Females with Turner syndrome have a wide chest and widely spaced nipples. They have cardiac defects and fertility problems.
Jacob syndrome (47 XYY)
Figure 4: 47,XYY
XYY syndrome occurs in 1 out of every 1,000 boys. Unlike other sex chromosome abnormalities, this condition does not have any effect on the man. Zygotes with XYY karyotype generally develop into fertile males. Many people with the condition are unaware that they have it. Some medical geneticists question whether the term "syndrome" is appropriate for this condition because many people with this karyotype appear normal. However, some studies show that men with XYY karyotype have aggressive behaviours. The researches in prisons show that serial killers usually have XYY karyotype.
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