Sex chromosomes determine an organism’s sex and are composed of interwoven strands of DNA. Humans have 22 autosomes and a pair of sex chromosomes, designated X and Y. XX indicates feminine traits, while XY indicates masculine traits. Abnormalities in sex chromosomes can result in genetic disorders and diseases.
A sex chromosome is a string-like structure within the nucleus of a cell that determines the sex of an organism. In humans, each cell normally has a pair of sex chromosomes designated by the letters X and Y. The presence of the Y chromosome distinguishes masculine from feminine traits. Most people have only one pair of these chromosomes in each cell, but some individuals have more or fewer of them, resulting in some genetic disorders.
Composed of interwoven strands of DNA, chromosomes are the building blocks of an organism’s genetic makeup. In the human body, the nucleus of each cell contains 22 chromosomes called autosomes and a pair of sex chromosomes. A single human sex chromosome is labeled as X or Y, and these chromosomes pair up as XX or XY. An XX designation means the person will have feminine traits, while an XY pair indicates the individual will have masculine characteristics. The particular biology of these chromosomes and the way they link together means that it is possible to have a pairing of two X’s but not two Y’s.
For females, during the embryonic stage of development, only the egg cell is allowed to carry two active X chromosomes. For all other cells that contain two X chromosomes, one will be disabled. During conception, when the egg containing two X chromosomes meets the sperm containing one X and one Y chromosome, a random pair is created, which includes either two X combinations or one XY combination.
Not only does a sex chromosome determine a person’s reproductive organs, but it is also responsible for other characteristics that are normally associated with either men or women. For example, a person who carries an XY sex chromosome typically develops a full beard, a prominent Adam’s apple, and a relatively deep voice. Conversely, individuals who have an XX chromosome normally develop distinctive female characteristics, such as mammary glands, enlarged breasts, and finer, thinner facial hair.
There are situations when a person has an abnormal pair of sex chromosomes. For example, sometimes an extra X attaches to the pair, or occasionally there is only one chromosome instead of two. In these cases, the person will likely develop certain disorders, such as Turner syndrome.
In other cases, the X chromosome may carry an abnormality that manifests itself as a particular disease, such as hemophilia or Duchene muscular dystrophy. These types of conditions are considered recessive as they are almost always exclusive to men. This is because for a woman to show symptoms, both X chromosomes would have to be defective. On the other hand, since a man has only one X chromosome, if he is defective, he will likely show symptoms of the disorder.
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