Y chromosome is minimizing its length but will not be extincted !!!

Thursday, May 28, 2009

All chromosomes in the nucleus come in pairs – except the Y chromosome. Each member of a chromosomal pair depends on its mate for genetic repair through sexual recombination. When one half suffers a genetic injury, it can discard the mutated gene and replace it with a normal copy drawn from the other member of the pair. But the Y has no sexual 'partner' with which to swap out defective genes.

However,Researchers from Whitehead Institute for Biomedical Research and Washington University School of Medicine suggested that Y chromosome includes a large number of genes arranged in pairs along this single chromosome in ways that may allow the Y to mimic the paired chromosome structure of the rest of the genome.

"Genes constantly are being bombarded with little injuries – mutations. Mutations can either be beneficial or detrimental, but they are far more often detrimental," said lead researcher David Page. "On the Y, detrimental mutations cannot be discarded."

There's no question that this inability to discard has cost the Y hundreds of genes over time. Many of the chromosome's genes either have weakened or died out altogether. Sexual recombination is a card game the Y just can't win. But this new research suggests it doesn't always need to. For critical genes, it swaps with itself.

Rather than swapping DNA with the X, the Y may exchange DNA with itself, in a recombination process mediated by the palindromes. The palindromes contain genes, so in effect the Y could be able to repair itself, replacing bad sequence with good, suggested by David Page.

"This study shows that the Y chromosome has become very efficient at preserving its important genes," said co-lead investigator Richard K Wilson. "It's found different ways to do the things that chromosomes must do to evolve, survive and thrive."

However, not all scientists r convincened by this! As Mark Jobling points out, the evolutionary cost of this mechanism is very high to occur !!!

reference:

http://genome.wellcome.ac.uk

Men on the road to extinction !!!

Monday, May 25, 2009

Professor Jennifer Graves, a leading researcher in human sex chromosome from australia, claims the male Y chromosome was dying and could run out within the next 5 million years.

While at the annual outreach public lecture at the Royal College of Surgeons in Ireland, Graves said,"You need a Y chromosome to be male." "Three hundred million years ago, the Y chromosome had about 1,400 genes on it, and now it's only got 45 left, so, at this rate, we're going to run out of genes on the Y chromosome in about five million years. The Y chromosome is dying and the big question is what happens then," she added.

 The male Y chromosome has a gene - SRY. SRY switches on the development of testes and pumps out male hormones that determine maleness. She said it was not known what would happen once the Y chromosome disappeared. 

"Humans can't become parthenogenetic, like some lizards, because several vital genes must come from the male," she said."But the good news is certain rodent species - the mole voles of Eastern Europe and the country rats of Japan - have no Y chromosome and no SRY gene. 

"Yet there are still plenty of healthy male mole voles and country rats running around. Some other gene must have taken over the job and we'd like to know what that gene is," she added.

Earliar in 2003,Brian sykes said, time will come when Y chromosome will cease to exist. Because,Over each replication hangs the threat of a random genetic mutation, which can be handed down to the next generation. Unlike other chromosomes, which are paired and can exchange genetic material with each other, the lowly Y has no duplicate from which to seek repair. Slowly but surely, Y chromosomes throughout the world are being pounded into submission.

Stem cells have the ability to grow into many other types of cell. if so, why its still not possible to grow a functional organ in the lab?

Friday, May 22, 2009

 Let's consider all of the things you would need to make an organ - say, a kidney - in a lab dish.

1. First, you need to obtain a type of stem cell that can ultimately become a kidney. Would this be an embryonic stem cell? A fetal stem cell? Will an adult stem cell do the job? How do you know? Where will you get the cells?
   
   
2. Next, you have to coax the stem cells to grow and divide in a lab dish. Which nutrients will help them grow? Do they need other types of cells around to encourage them to divide? If so, can you obtain them?
   
   
3. After you have enough stem cells, you must simulate the physical environment required for them to differentiate into a functional kidney. How do you make the cells begin differentiating? Can you simulate the physical environment they need? Can you create a physical scaffold, or foundation, upon which the cells can shape themselves into a kidney? How will you help the developing kidney grow blood vessels to supply oxygen and nutrients to cells on the interior?
   
   

Scientists are still years away from growing whole human organs in lab dishes - but not for lack of trying. Research groups around the world have convinced various types of stem cells to grow, divide and even differentiate in lab dishes. Most of this research is performed in stem cells obtained from other organisms, such as mice, rats and frogs.

The final step, creating a functional organ out of differentiating stem cells, is more challenging. Obstacles to success include the problem of delivering oxygen and nutrients to cells on the inside of the organ, as well as creating physical scaffolds upon which to grow and differentiate cells.

reference:

http://learn.genetics.utah.edu