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Table of Contents
EDITORIAL
Year : 2015  |  Volume : 2  |  Issue : 2  |  Page : 14-15

Why only Y-?


1 Chief Editor, Acta Medica International, Teerthanker Mahaveer University, Moradabad, India
2 Journal Administrator, Acta Medica International, Teerthanker Mahaveer University, Moradabad, India
3 Academic Editor, Acta Medica International, Teerthanker Mahaveer University, Moradabad, India

Date of Web Publication5-Jul-2017

Correspondence Address:
Nidhi Sharma
Journal Administrator, Acta Medica International, Teerthanker Mahaveer University, Moradabad
India
Rohin Garg
Academic Editor, Acta Medica International, Teerthanker Mahaveer University, Moradabad
India
Sanjeev Kumar Jain
Chief Editor, Acta Medica International, Teerthanker Mahaveer University, Moradabad
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.5530/ami.2015.2.4

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How to cite this article:
Jain SK, Sharma N, Garg R. Why only Y-?. Acta Med Int 2015;2:14-5

How to cite this URL:
Jain SK, Sharma N, Garg R. Why only Y-?. Acta Med Int [serial online] 2015 [cited 2019 Sep 21];2:14-5. Available from: http://www.actamedicainternational.com/text.asp?2015/2/2/14/209631





In accordance with the Bible man is considered as the first sex and female the second.

The Sex chromosomes X and Y-chromosomes evolved from a pair of autosomes about 200-300 million years ago.[1],[2]

Drosophila melanogaster and humans are two species in which Y-chromosome has been studied the best. (Lahn et al. 2001)[3]

Y-chromosome was named by American Geneticist Nettie Stevens. In humans, the Y chromosome is about 23-Mb in size which codes for 78 protein, compared to 150-Mb of X-chromosome which encodes for 800 proteins. The most important function of Y- chromosome is sex determination, and the first genes identified on the Y included candidates for the testis-determining gene, SRY. There occurred a mutation in SOX3 to form SRY gene,which is responsibe for maleness, on Y chromosome.

Y-chromosome looses most of its original genes over evolutionary time.[4]

Human Y-chromosome attracted attention of many evolutionary geneticists since long because of the unique transmission pattern. Genomic data confirms that Y-chromosome breaks the law of evolution, that's why some scientists also name it perversive chromosome.

There is universal acceptance of the fact that Y chromosomes degrade but widespread and vigorous debate about the rate at which this occurs.

What causes Y degradation? There are two accepted phenomenon in human beings first is higher mutation rate,[5] and second the inefficiency of selection on a non- recombining chromosome.[6],[7]

Inversions, lead to rearrangement of genes which restrict large portions of the X and Y chromosome to recombine, which made the Y chromosome susceptible to deletions, and it decrease in size. Large portion of Drosophila melanogaster and human Y-Chromosome contains “junk” DNA.[8]

As the evolution of Y-chromosome occured inversion further scrambled the genes on Y. Due to this Y-chromosome were left able to recombine with homologous genes on the X chromosome. Whereas in females, recombination to occuedr across the full length of the two identical X chromosomes.

Jennifer Graves of Australian National University leading experts in Y-chromosome phylogeny is of the opinion that the Y is on the road to extinction. She estimated that since the Y took on its sex-determining role, 1393 out of 1438 genes lost. Graves argues that the Y chromosome's significant rate of gene loss (4.6 genes every million years) guarantees its future demise. Contrary to Graves, David Page of the Massachusetts Institute of Technology claimed that the Y chromosome does not have only 27 genes in the MSY, but 78. He further added that the Y's power of self-preservation have been extraordinary.

Y-chromosomes due to its genetic strucure has lost its power of recombination except for very small pseudoautosomal regions and has lost its most of the genes. Male limited transmission is another cause of Y-chromosome degeneration. On an average rate of loss of active genes from the human Y-Chromosome predicted its extinction in 10 million years or so. One of the biggest mysteries in evolutionary genetics is what are the forces which lead to degeneration of nonrecombining regions of the Y, and why natural selection for male-advantage genes does not stop it. Would degeneration of the Y lead to male extinction? No cheering evidence that a revolution in Y- sex chromosomal not herald the collapse of human reproduction. There are many novel genetic mechanisms in which a new sex-determining system could replace the old,without any changes being evident.

However, recent experimental studies have clearly suggested that Y degeneration does not proceed in simple linear fashion and refute these sensational claims of Y-Chromosome extinction.[9]

Many experimental studies strongly suggest that TEs (Transposable elements) play an important role in the process of Y-chromosome degeneration. In conclusion we can expect there are, a diverse array of changes at molecular level which contributes to degeneration of Y-chromosone.



 
  References Top

1.
Charlesworth, B. The evolution of chromosomal sex determination and dosage compensation. Curr. Biol. 1996; 6: 149–162.  Back to cited text no. 1
    
2.
Lahn BT, Page DC. Four evolutionary strata on the human X chromosome. Science. 1999; 286:964–967. [PubMed: 10542153]  Back to cited text no. 2
    
3.
Lahn, B.T., Pearson, N.M., and Jegalian, K. The human -chromosome, in the light of evolution. Nat. Rev. Genet. 2001; 2: 207–216.  Back to cited text no. 3
    
4.
Charlesworth B, Charlesworth D. The degeneration of Y chromosomes. Philos Trans R Soc Lond B Biol Sci. 2000; 355:1563–72. [PubMed: 11127901]  Back to cited text no. 4
    
5.
Innocenti P, Morrow EH. The Sexually Antagonistic Genes of Drosophila melanogaster. Plos Biology. 2010; 8  Back to cited text no. 5
    
6.
Rice WR. Genetic hitchhiking and the evolution of reduced genetic activity of the Y sex chromosome. Genetics. 1987; 116:161–167. [PubMed: 3596229]  Back to cited text no. 6
    
7.
Orr HA, Kim Y. An adaptive hypothesis for the evolution of the Y chromosome. Genetics. 1998;150:1693–8. [PubMed: 9832543]  Back to cited text no. 7
    
8.
Carvalho, A.B., Dobo, B.A., Vibranovski, M.D., and Clark, A.G.Identification of five new genes on the Y chromosome of Drosophila melanogaster. Proc. Natl. Acad. Sci. 2001; 98: 13225–13230.  Back to cited text no. 8
    
9.
Hughes JF, et al. Strict evolutionary conservation followed rapid gene loss on human and rhesus Ychromosomes. Nature. 2012; 483:82–U124. [PubMed: 22367542]  Back to cited text no. 9
    




 

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