In the nucleus of each cell, DNA molecules are packed into linear structures called chromosomes. Each chromosome is made up of DNA that is tightly wound several times around a protein called histone that supports its structure.
When the cell is not dividing, even under the microscope, the chromosomes do not appear in the nucleus. However, the DNA that forms the chromosomes hardens during cell division and then appears under the microscope. Most of what researchers know about chromosomes is learned by looking at chromosomes during cell division.
Each chromosome has a contraction point called the centromere, which divides the chromosome into two parts, the “arm”. The short arm of the chromosome is called the “P-arm”. The long arm of the chromosome is called the “Q arm”. The location of the centromere on each chromosome gives the chromosome its distinctive shape and can be used to help describe the location of a particular gene.
Structure of X and Y Chromosomes
In other parts of the human body, chromosomes have the same shape and size (same pair), while X and Y chromosomes have different structures.
The X chromosome is longer than the Y chromosome and contains hundreds more genes. Since the other genes of the X chromosome have no counterpart in the Y chromosome, the X gene is predominant. This means that almost all genes on X, even if it is recurrent in females, will be expressed in males. These are called X-linked genes. Genes found only on the Y chromosome are called Y-linked genes and are expressed only in males. The gene on any sex chromosome can be called a sex-related gene.
There are approximately 1,098 X-linked genes, although most of them do not have female physiological characteristics. In fact, many diseases are related to diseases such as hemophilia, Duchenne muscular dystrophy, and Fragile X syndrome. They are the cause of red-green color blindness and are considered the most common genetic disease in men. Non-sex trait X-linked genes are also related to male pattern baldness.
Unlike the large X chromosomes, the Y chromosome contains only 26 genes. Sixteen of these genes are responsible for cell maintenance. Nine are involved in sperm production, and if some of them are missing or defective, a low sperm count or infertility may occur. A gene called the SRY gene is responsible for male traits. The SRY gene triggers the activation and regulation of another gene called the SRY gene on the non-sex. SRY gene triggers the development of non-gonads in the testes rather than in the ovaries.
Sex Chromosome Abnormalities
An unusual combination of sex chromosomes can lead to many types of sex-specific diseases, which are rarely fatal.
According to the National Library of Medicine, female abnormalities can cause Turner syndrome or trisomy X. Turner syndrome occurs when a woman has only one X chromosome instead of two. Symptoms include the inability of the sex organs to mature normally, leading to infertility, small breasts and no menstruation. Short, broad shield-shaped chest; And wide-necked neck.
Trisomy X syndrome is caused by three X chromosomes instead of two. Symptoms include lengthening, slow speech, premature ovarian failure or abnormal ovulation, and weak muscle tone — although many girls and women have no symptoms.
Men can be affected by Klinefelter syndrome. Symptoms include breast enlargement, abnormal proportions, such as large buttocks, height, infertility, and small testicles.
- Nucleus: Define its Structure & Function
- Cytoplasm: Define Its Function, Structure, and Location
- Ribosomes Function: Define Its Structure, Size, Location