Difference Between X and Y Chromosome: The genome is the data repository that supplies information about the expression of genes and various traits of living beings. Deletion or modification to a single nucleotide of a gene might lead to a huge impact. Let us understand the difference between the X and Y chromosomes of humans here. Also, know what might happen to the Y chromosome in the future, which is thousands of years away.
Human Chromosomes
The length of human DNA (deoxyribonucleic acid) is around 2.2 meters, which condenses into the 23 pairs of chromosomes to be packed into the cells with nanometre diameters. This fascinating science is responsible for the sustainance of life and the expression of various proteins that determine the characteristics of living beings. The chromosomes are divided into two categories: autosomes and sex chromosomes.
Autosomes: The 22 pairs of chromosomes that do not have any role in determining the sex of the baby are called autosomes. They are responsible for the other major traits of the body. Thus, there are 44 autosomes.
Sex Chromosomes: The 23rd pair of chromosomes involved in sex determination and expression of major sex hormones and thus are called sex chromosomes. There are two sex chromosomes in humans, X and Y.
What is the X Chromosome?
The X chromosome is one of the sex chromosomes that is involved in the sex determination of the foetus. In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
The size of the X chromosome is larger than the Y chromosome and thus contains more genes that express proteins, which are responsible for the wide variety of functions in the body. Determination of physical traits, brain development, and development of secondary sexual characteristics are some of the major roles of the X chromosome. Even though females possess two copies of the X chromosome, one of those remains inactive and only becomes active during the gamete formation phase.
Certain genetic conditions, like haemophilia and colour blindness, are linked to mutations on the X chromosome. These are known as X-linked disorders, and they often affect males more frequently because they have only one X chromosome.
What is the Y Chromosome?
The Y chromosome is one of the sex chromosomes that play a crucial role in sex determination in human males. In humans, only males contain a single copy of the Y chromosome along with a copy of the X chromosome. Thus, human males have XY sex chromosomes.
The size of the Y chromosome is smaller than the X chromosome, and thus it contains a smaller number of genes that are essential for males. Its primary role is to carry the SRY gene, which triggers the development of male physical traits, including the formation of testes and the production of male hormones like testosterone. The Y chromosome is passed from father to son, meaning it is inherited only through the male line. It also plays a role in sperm production, making it essential for male fertility.
Difference Between X and Y Chromosomes
The table below shows the key differences between X and Y chromosomes that can be used by students as it is to write in the exams.
| Feature | X Chromosome | Y Chromosome |
| Presence in Gender | Present in both males and females | Present only in males |
| Number per Cell | Two in females (XX), one in males (XY) | One in males (XY), absent in females (XX) |
| Size | Larger and contains more genes | Smaller and contains fewer genes |
| Genetic Material | Carries genes responsible for various traits | Carries genes mainly related to male traits |
| Sex Determination | Does not determine sex alone | Determines male sex when paired with X |
| Recombination | Recombines with another X chromosome in females | Does not recombine, except at the tips with X (pseudoautosomal region) |
| Inheritance | Inherited from both parents | Inherited only from the father |
| Associated Disorders | X-linked disorders like haemophilia and colour blindness | No major genetic disorders, but can carry Y-linked traits |
| Function in Females | One X chromosome in females is usually inactivated (Barr body) | Not present |
| Function in Males | Active and contributes to traits and characteristics | Determines male characteristics and plays a role in sperm production |
Will Male Y Chromosome Disappear in Future?
Over the years, evolution and environmental factors have played a role in changing the expression of the genome. The genome studies conducted on many species have shown the complete elimination of the Y chromosome from their karyotype. This means there are species like the mole voles of eastern Europe and the spiny rats of Japan who have already lost their Y chromosome. Now the question arises, whether human males will lose their Y chromosome too?
Well, the answer to this is almost out. The idea that the Y chromosome might shrink in the future is based on scientific observations that the Y chromosome has already become smaller over evolutionary time. Some scientists speculate that this process of shrinking, known as "genetic decay," could continue, potentially leading to the Y chromosome losing more of its remaining genes. In the distant future, if the Y chromosome continues to shrink, it could theoretically disappear entirely. However, this process would take millions of years, if it happened at all.
As per the recent studies, the genes of the Y chromosome will gradually relocate to other sites on DNA. Thus, there are possibilities that the chromosome might shrink, but the genes will still be there, distributed all across the DNA. And thus, male factors still have chances of survival.
Sources:
- How to manage without a Y chromosome. Proceedings of the National Academy of Sciences, 120(2), e2218839120.
- Turnover of mammal sex chromosomes in the Sry-deficient Amami spiny rat is due to male-specific upregulation of Sox9. Proceedings of the National Academy of Sciences, 119(49), e2211574119.
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