探索世界奥秘之The Ghost In Your Genes(基因外遗传现象) Unit04

...lead to the end of diseases like cancer...

Alzheimer's, Parkinson's, diabetes.

The list is endless.

We were thinking of genes in a very mechanical way. We were thinking of them just in terms of the sequence of the letters when we were working out how we could work out what all the letters were in the book.

Scientists estimated that the human genome, the book of life, would contain around 100,000 genes.

And then when they started sequencing they, they realized there may be 100,000 genes, and it popped down to 60, and then it popped down to 50, I mean, and slowly went down to a much smaller number. In fact we found out that the human genome is probably not as complex and doesn't have as many genes as, as plants do. So that they made us really question it all. If the genome has less genes in this species versus this species, and we are more complex potentially, what's going on here?

Now, scientists estimate there are probably less than 30,000 genes.

We believed, I believed naively that we would be able to find the genetic components of common diseases. That's proven to be very difficult. The idea of one-gene-one-disease does not explain it all.

30,000 genes didn't appear enough to explain human complexity. There had to be something they'd missed. The first hints of what was missing lay in the curious paradox of the Prader-Willi and Angelman syndromes, two quite different diseases caused by exactly the same genetic fault. When Pembrey looked at the inheritance pattern for their conditions he noticed something even stranger.

What really mattered was the origin of the Chromosome 15 that had the deletion. If the deletion was on the Chromosome 15 that the child had inherited from father then you had Prader-Willi syndrome. Whereas, if the, er, deletion, er, was inherited from the mother, er, you had the Angelman syndrome.

It was a complete surprise that the same missing strip of DNA could cause one disease when it came from the mother and a completely different disease when it came from the father. It was as if the genes knew where they came from.

You've got a developing fetus manifesting this condition. How does the Chromosome 15 know where it came from? It, there must have been a tag or an imprint placed on that chromosome during either egg or sperm formation in the previous generation to, to say "Hi, I came from mother, I came from father" and we are functioning differently. So that's the key thing that although the DNA sequence is the same the different sets of genes were being silenced depending on whether it came from the mother or from the father.

New Words & Phrases:

Alzheimer's: Alzheimer's disease is a condition in which a person's brain gradually stops working properly. 【医】阿耳茨海默氏病,早老性痴呆病

Parkinson's: 【医】帕金森氏病
fetus : (= foetus)A fetus is an animal or human being in its later stages of development before it is born. 胎;(三个月后的)胎儿