शुक्रवार, 25 अप्रैल 2014

Y chromosome appeared in mammals 180m years ago

Y chromosome appeared 

in mammals 180m 

years ago

LONDON: Scientists have found that the first sex determining genes appeared in mammals some 180 million years ago. In humans and other mammals, the difference between sexes depends on one single element of the genome: the Y chromosome. It is present only in males where the two sexual chromosomes are X and Y whereas women have two X chromosomes. 

A team from the Swiss Institute of Bioinformatics found that a very long time ago X and Y were identical until the Y started to differentiate from the X in males. It then progressively shrank to such an extent that now it only contains about 20 genes (the X carries more than one thousand genes). 

They have now established that the first sex genes appeared concomitantly in mammals around 180 million years ago. The study required more than 29,500 computing hours and involved working with samples from 15 different mammals representing these three lineages as well as the chicken which they included for comparison.

By studying samples from several male tissues — in particular testicles — from different species, the researchers recovered the Y chromosome genes from the three major mammalian lineages: placentals (which include humans), marsupials and monotremes.

Instead of sequencing all Y chromosomes, the scientists opted for a shortcut. By comparing genetic sequences from male and female tissues they eliminated all sequences common to both sexes in order to keep only those sequences corresponding to the Y chromosome. By doing so they established the largest gene atlas of this male chromosome to date. The study shows that the same sex-determining gene named SRY in placentals and marsupials had formed in the common ancestor of both lineages around 180 million years ago.

  • Marsupial

  • Marsupials are an infraclass of mammals living primarily in Australasia and the New World. A distinctive 

  • characteristic, common to most species, is that the young are carried in a pouch.

  • कोई भी ऑस्ट्रेलियाई पशु जिसमें मादा अपने बच्चे को पेट पर लगी 

  • थैली 

  • में ले जाती है ,शिशुधानी वाले पशु मासूपियल कहलाते हैं 

  • Monotreme

  • Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental 
  • mammals. Wikipedia

  • Scientific nameMonotremata

  • यह एक प्रकार की ऐसी पशु प्रजाति है जिसकी मादा अंडे तो देती है लेकिन अपने शावकों को दुग्धपान भी करवाती है। इसके उदाहरण 

  • के 

  • रूप में ECHIDNA एवं PLATYPUS को गिनाया जा सकता है। 

  • आधुनिक मानवों में पुरुष एक ऐसी शख्शियत है जो वाई -एक्स गुणसूत्र लिए है जबकि महिला एक्स -एक्स लिए रहती है। धीरे धीरे 

  • पुरुष में वाई गुणसूत्र का छीज़ना शुरू हुआ जो छीज़ते छीज़ते अपने जीवन खंड बौलांश में गँवा बैठा ले देकर आज ३० जीवन  इकाइयां 

  • (GENS )ही वाई गुणसूत्र पर सुनिश्चित स्थानों पर विद्यमान हैं जबकि एक्स गुणसूत्र पर हज़ार से ज्यादा आनुवंशिक इकाइयां 

  • (GENES )विराजमान रहतीं हैं। 

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