Key Difference – X vs Y Chromosomes
The human genome has 46 chromosomes, arranged in 23 pairs. There are two sex chromosomes (one pair) among them known as X and Y chromosome. These two chromosomes are designated as gender determination chromosomes. Every man has X and Y chromosome and Y chromosome decides the male sex. Every woman has two X chromosomes. The key difference between X chromosome and Y chromosome is that X chromosome does not contain SRY gene (sex-determining region Y), which is the male determining gene while Y chromosome has SRY gene. X chromosome is larger in size and contains a higher number of genes compared to Y chromosome. Y chromosome is smaller in size and contains only a few number of genes.
CONTENTS
1. Overview and Key Difference
2. What are X Chromosomes
3. What are Y Chromosomes
4. Side by Side Comparison – X vs Y Chromosomes
5. Summary
What are X Chromosomes?
X chromosome is one of the sex chromosomes in humans which relates to the sex determination and reproduction. The shape of the X chromosome takes the letter X of the alphabet. It contains about 155 million base pair of DNA and represents approximately 5% of total DNA of a cell in a female. Each human has at least one X chromosome in his chromosome set. Females have two X chromosomes while males have X and Y chromosome. One of the X chromosome in the female is inherited from the mother and the other X chromosome is inherited from the father. Males inherit their X chromosome exclusively from the mother.
X chromosome five times larger than the Y chromosome. The number of genes borne by the X chromosome is many times the number of genes born by the Y chromosome. There are unique genes located in X chromosome. Both X and Y chromosomes have a pseudoautosomal region. The genes in that region are common to both chromosomes and are involved in the normal development of the organism.
X chromosome has more than 1000 genes that encode various proteins. These proteins perform various functions in the body. However, the X chromosome may have genes that cause diseases. They are known as X linked genes. Since women have two X chromosomes, their X linked disease occurrence is high compared to men. X linked diseases are transmitted to men from his mother. A daughter can get the X linked diseases from her affected father. For example, hemophilia A is a X linked disease which can be transmitted from affected father to his daughter.
Figure 01: X chromosome
What are Y Chromosomes?
Y chromosome is one of the sex chromosomes in the human genome. It is in the genome of men and is considered as one of the smallest chromosomes in the human genome. The presence of Y chromosome decides the male sex of a boy. It carries a male-determining gene called SRY gene. The expression of SRY gene results in a protein called SRY protein, which starts a process that causes the development of testes and the prevention of female reproductive structure development. The shape of the Y chromosome resembles the letter Y in the alphabet. The size of the Y chromosome is smaller than X chromosome. Hence, it contains a lesser number of genes (about 50 genes) compared to X chromosome. Some genes are unique to Y chromosome while the genes located in the pseudoautosomal region are shared with X chromosome. Most of the genes located on the Y chromosomes are associated with male fertility.
Figure 02: Y chromosome
What is the difference between X and Y Chromosomes?
X vs Y Chromosomes |
|
| X chromosome is one of the two sex chromosomes in humans. | Y chromosome is one of the two sex chromosomes in humans. |
| Shape | |
| Shape of the chromosome resembles X letter in the alphabet. | Shape of the Y chromosome resembles letter Y in the alphabet. |
| Inheritance | |
| Males have one X chromosome inherited from mother and females have two X chromosomes inherited from both parents. | Only male genome contains Y chromosome; this is inherited from the father. |
| Size | |
| X chromosome is five times larger in size than Y chromosome. | Y chromosome is smaller in size and is one of the smallest chromosomes in the human genome. |
| Gene Content | |
| X chromosome contains about 1000 genes, which is many times the number in Y chromosomes. | Y chromosome contains 50 to 60 genes. |
| SRY Gene | |
| X chromosome does not contain SRY gene. | Y chromosome has an SRY gene. |
Summary – X vs Y Chromosomes
Humans have one pair of sex chromosomes out of total 23 pairs of chromosomes in his genome. They are named as X and Y chromosome. They resemble the shapes of letters X and Y of the alphabet, respectively. Together with the Y chromosome, X chromosome plays a vital role in the determination of sexes. X chromosome is larger than Y chromosome and bears a higher number of genes unique to it. Females have two X chromosomes while males have only one X chromosome. Males have both types of sex chromosomes X and Y. Y chromosome contains a male-determining gene called SRY gene. Hence, sex of a boy is fully decided by the Y chromosome. This is the difference between X and Y chromosomes.
Reference:
1. “X chromosome – Genetics Home Reference.” U.S. National Library of Medicine. National Institutes of Health, n.d. Web. 23 May 2017. https://ghr.nlm.nih.gov/chromosome/X
2. “X Chromosome.” Genetics. Encyclopedia.com, n.d. Web. 23 May 2017. http://www.encyclopedia.com/science-and-technology/biology-and-genetics/genetics-and-genetic-engineering/x-chromosome
3. Arnold, Arthur P., Xuqi Chen, and Yuichiro Itoh. “What a difference an X or Y makes: sex chromosomes, gene dose, and epigenetics in sexual differentiation.” Handbook of experimental pharmacology. U.S. National Library of Medicine, 2012. Web. 23 May 2017
Image Courtesy:
1. “Human chromosome X – 400 550 850 bphs” By National Center for Biotechnology Information, U.S. National Library of Medicine – (Public Domain) via Commons Wikimedia
2. “Human chromosome Y – 400 550 850 bphs” By National Center for Biotechnology Information, U.S. National Library of Medicine (Public Domain) via Commons Wikimedia