கண்ணில் முளைத்த கால்!

இது சாதாரண பழம் தின்னும் ஈ Normal fruit fly head.


இது ஈக்களின் கண்ணில் ஆண்டெனாவுக்கு பதிலாக கால் முளைத்த ஈ
(fruit fly)
Fruit fly head showing the effects of the Antennapedia gene. This fly has legs where its antennae should be.
FLYBASE; R. TURNER

மனிதர்கள் உடலில் இருக்கும் புரோட்டீன்களில் முக்கியமானவை எப்படி ஆரம்ப செல்கள் வளர்கின்றன என்பவற்றை கட்டுப்படுத்துபவை.

இந்த புரோட்டீன்கள் எவ்வாறு வேலை செய்கின்றன என்பதனை எப்போது அவைகள் தவறாக வேலை செய்கின்றபோது கண்டறியலாம்.

இந்த கண்ணில் முளைத்த கால், பரிணாமம் என்ற அறிவியலை மனிதர்கள் புரிந்த்கொள்ள மிகவும் உதவியது.

ஒரு உயிரிலிருந்து இன்னொரு உயிர் உருவாகும்போது டி.என்.ஏ காப்பி செய்யப்படும்.

அந்த காப்பியின் போது நடக்கும் சின்ன சின்ன தவறுகள் கூட எப்படி பெரிய விளைவுகளாக வரும் என்பதற்கு இந்த கண்ணில் முளைத்த கால் ஒரு உதாரணம்

An Interesting Development

In the human body, one of the most important jobs for proteins is to control how embryos develop. Scientists discovered a hugely important set of proteins involved in development by studying mutations that cause bizarre malformations in fruit flies.

The most famous such abnormality is a fruit fly with a leg, rather than the usual antenna, growing out of its head. According to Thomas C. Kaufman of Indiana University in Bloomington, the leg is perfectly normal—it's just growing in the wrong place.

Normal fruit fly head.
Fruit fly head showing the effects of the Antennapedia gene. This fly has legs where its antennae should be.
FLYBASE; R. TURNERIn this type of mutation and many others, something goes wrong with the genetic program that directs some of the cells in an embryo to follow developmental pathways, which are a series of chemical reactions that occur in a specific order. In the antenna-into-leg problem, it is as if the cells growing from the fly's head, which normally would become an antenna, mistakenly believe that they are in the fly's thorax, and therefore ought to grow into a leg. And so they do.

Thinking about this odd situation taught scientists an important lesson—that the proteins made by some genes can act as switches. Switch genes are master controllers that provide each body part with a kind of identification card. If a protein that normally instructs cells to become an antenna is disrupted, cells can receive new instructions to become a leg instead.

Scientists determined that several different genes, each with a common sequence, provide these anatomical identification card instructions. Kaufman isolated and described one of these genes, which became known as Antennapedia, a word that means "antenna feet."

Kaufman then began looking a lot more closely at the molecular structure of the Antennapedia gene. In the early 1980s, he and other researchers made a discovery that has been fundamental to understanding evolution as well as developmental biology.

The scientists found a short sequence of DNA, now called the homeobox, that is present not only in Antennapedia but in the several genes next to it and in genes in many other organisms.When geneticists find very similar DNA sequences in the genes of different organisms, it's a good clue that these genes do something so important and useful that evolution uses the same sequence over and over and permits very few changes in its structure as new species evolve.

Researchers quickly discovered nearly identical versions of homeobox DNA in almost every non-bacterial cell they examined—from yeast to plants, frogs, worms, beetles, chickens, mice, and people.

Hundreds of homeobox-containing genes have been identified, and the proteins they make turn out to be involved in the early stages of development of many species. For example, researchers have found that abnormalities in the homeobox genes can lead to extra fingers or toes in humans.

நன்றி
http://publications.nigms.nih.gov/thenewgenetics/chapter1.html