owolves, Article 40 nesticated us against s. And b organ- e did with e and Bless
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owolves, Article 40 nesticated us against s. And b organ- e did with e and Blessing of the Ghetto getting Though Tay-Sachs disease is a choosy killer, one that for centuries targeted Eastern European Jews above all others. By decoding its lethal logic, we can learn lot about how genetic diseases evolve-and how they can be conquered. wly built y. It may old term. it may nal, whenJARED DIAMOND I haven't swers, its Mininghardt de elpful. As our obstetrician s ge arie and I hated her at first sight, even though she was In peoples around the world Tay-Sachs appears once in trying hard to be helpful. As our obstetrician's genet every 400,000 births. But it appears a hundred times more ics counselor, she was just doing her job, explaining frequently-about once in 3,600 births-among descendants to us the unpleasant results that might come out of the genetic of Eastern European Jews, people known as Ashkenazim. For lests we were about to have performed. As a scientist, thoughI descendants of most other groups of Jews-Oriental Jews, already knew all I wanted to know about Tay-Sachs disease, and chiefly from the Middle East, or Sephardic Jews, from Spain Ididn't need to be reminded that the baby sentenced to death by and other Mediterranean countries-the frequency of Tay Sachs disease is no higher than in non-Jews. Faced with such a Fortunately, the tests would reveal that my wife and I were clear correlation, one cannot help but wonder: What is it about not carriers of the Tay-Sachs gene, and our preparenthood fears s one group of people that produces such an extraordinarily eventu- answers chemists t qui peoples a und the world birsaa unappedes enda re withs do with uld only re doing ally this re. it could be my own. on that matter at least could be put to rest. But at the time I high risk of this disease? didn't yet know that. As I glared angrily at that poor genetics Finding the answer to this question concerns all of us, regard- counselor, so strong was my anxiety that now, four years later, I less of our ancestry. Every human population is especially sus- can still clearly remember what was going through my mind: If ceptible to certain diseases, not only because of its life-style Iwere an evil deity, I thought, trying to devise exquisite tortures but also because of its genetic inheritance. For example, genes for babies and their parents, I would be proud to have designed put European whites at high risk for cystic fibrosis, African blacks for sickle-cell disease, Pacific Islanders for diabetes- Tay-Sachs is completely incurable, unpreventable, and pre and Eastern European Jews for ten different diseases, including programmed in the genes. A Tay-Sachs infant usually appears Tay-Sachs. It's not that Jews are notably susceptible to genetic normal for the first few months after birth, just long enough for diseases in general; but a combination of historical factors has the parents to grow to love him. An exaggerated "startle reac led to Jews' being intensively studied, and so their susceptibili- w a free- Tay-Sachs disease ties are far better known than those of, say, Pacific Islanders. tion" to sounds is the first ominous sign. At about six months the baby starts to lose control of his head and can't roll over or Tay-Sachs exemplifies how we can deal with such diseases; it sit without support. Later he begins to drool, breaks out into has been the object of the most successful screening program to unmotivated bouts of laughter, and suffers convulsions. Then date. Moreover, Tay-Sachs is helping us understand how ethnic his head grows abnormally large, and he becomes blind. Per diseases evolve. Within the past couple of years discoveries by haps what's most frightening for the parents is that their baby molecular biologists have provided tantalizing clues to precisely loses all contact with his environment and becomes virtually how a deadly gene can persist and spread over the centuries. Tay a vegetable. By the child's third birthday, if he's still alive, his Sachs may be primarily a disease of Eastern European Jews, but skin will turn yellow and his hands pudgy. Most likely he through this affliction of one group of people, we gain a window die before he's four years old. on how our genes simultaneously curse and bless us all My wife and I were tested for the Tay-Sachs gene because The disease's hyphenated name comes from the tw at the time we rated as high-risk candidates, for two reasons. physicians-British ophthalmologist W. Tay and New York First, Marie was carrying twins, so we had double the uu urologist B. Sachs -who independently first recognized the chance to bear a Tay-Sachs baby. Second, both she and I are of disease, in 1881 and 1887, respectively. By 1896 Sachs had Eastern European Jewish ancestry, the population with by far seen enough cases to realize that the disease was most common the world's highest Tay-Sachs frequency among Jewish children.Explanation / Answer
Answer:-
In people around the globe Tay-Sachs appears in every 400000 births. But the frequency of the disease is hundred times more about 3600 births among the descendants of Eastern European Jews , people known as Ashkenazim. Every ethinic group has some kind of disease evolved with during the course of decades. However, Tay-Sachs is helping us understand how ethnic diseases evolve. Tay sachs may be a disease of Eastern European Jews, but through this affliction of one group of people, we gain a window on how our genes simultaneously curse and bless us all.
From there biblical home of ancient Israel, Jews spread peacefully to other Mediterranean lands, Yemen and India. They also dispersed violently through conquest by Assyrians, Babylonians and Romans. There the Jews stayed for centuries, through periods of both tolerance and oppression. But toward the end of the nineteenth century and the beginning of the twentieth, waves of murderous anti-Semitic attacks drove millions of Jews out of the Eastern Europe, with most of them heading United States. Most of the Jews who stayed in Eastern Europe were exterminated during the World War II, while most of the survivors immigrated to United States and Israel.
Of the 13 million Jews alive today, more than three quarters are Ashkenazim, the descendants of Eastern European Jews and the people most at the risk of Tay Sachs.
Have these Jews maintained their genetic distinctness through thousands of years? Some scholars claim there has been so much intermarriage and conversion that Ashkenazic Jews are now just Eastern Europeans who adopted Jewish culture. The four possible explanation for the persistence of the Tay- Sachs gene.
First, new copies of the gene might be arising by mutation as fast as existing copies disappear with the death of Tay-Sachs children, That’s the most likely explanation for the gene’s persistence in most of the world, where the disease frequency is only one in 400000 birth- that frequency reflects a typical high mutation rate. There would be no precedent for one particular gene mutating so much more often in one human population than in others.
As a second possibility, the Ashkenazim might have acquired Tay-Sachs from some other people who already had the gene at high frequency.
The third hypothesis was the one preferred by many geneticist. It invokes two genetic processes, termed as Founder effect and genetic drift, that may operate in small populations.
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