基因突變產生的十大特異功能(上)

Compared to many other species, all humans have incredibly similar genomes. However, even slight variations in our genes or environments can cause us to develop traits that make us unique. These differences can manifest in ordinary ways, such as through hair color, height, or facial structure, but occasionally, a person or population develops a characteristic that distinctly sets them apart from the rest of the human race.

和其他物種相比，人類有着令人難以置信的基因組。然而，我們的基因或環境的些微改變也可能導致我們發展出與衆不同的特點。這些差異一般都以普通的方式表現出來，例如頭髮顏色、身高、面部結構等。不過，某個或某一類人有時也會發展出截然不同地、區別於其他人類的典型特徵。

't Get High Cholesterol

10.膽固醇不會增高

While most of us have to worry about limiting our intake of fried foods, bacon, eggs, or anything that we're told is on the "cholesterol-raising list" of the moment, a few people can eat all these things and more without fear. In fact, no matter what they consume, their "bad cholesterol" remains virtually non-existent.

我們大多數人都擔心油炸食品如培根、雞蛋或其他會增加膽固醇的食物的攝入量。不過有少數人可以肆無忌憚地吃，不需要擔心膽固醇會因此增加。事實上，不論他們吃什麼，他們的壞膽固醇並不存在。

These people were born with a genetic mutation. More specifically, they lack working copies of a gene known as PCSK9, and while it's usually unlucky to be born with a missing gene, in this case, it seems to have some positive side r scientists discovered the relationship between this gene (or lack thereof) and cholesterol about 10 years ago, drug companies have worked frantically to create a pill that would block PCSK9 in other individuals. The drug is close to getting FDA approval. In early trials, patients who have taken it have experienced as much as a 75-percent reduction in their cholesterol far, scientists have only found the mutation in a handful of African Americans, and those with it have the benefit of a 90-percent reduced risk of heart disease.

這些人出生時基因發生了突變，說得更具體些，他們缺少有效的PCSK9基因對，一般來說，出生時丟失基因是件不幸的事，不過，在這種情況下，它反而產生了有益的效果。自從10年前，科學家們發現了PCSK9基因（缺失）與膽固醇之間的關係後，便開始瘋狂地研究能夠阻止PCSK9的藥物。該藥物獲美國食品與藥物管理局（ FDA ）批准的可能性很高。在早期的實驗中，服用此藥的病人的膽固醇水平減少了75%。到目前爲止，科學家們只在極少數的非裔美國人中發現了這種突變。這些人患心臟疾病的風險比常人降低了90%。

stance To HIV

9.抵抗艾滋病毒

All sorts of things could wipe out the human race—asteroid strikes, nuclear annihilation, and extreme climate change, just to name a few. Perhaps the scariest threat is some type of super-virulent virus. If a disease ravages the population, only the rare few who are immune would have a chance of survival. Fortunately, we know that certain people are indeed resistant to particular diseases.

能夠毀滅人類的東西可謂多矣：小行星撞擊、核打擊、極端氣候變化，等等。不過，最恐怖的威脅要數某些類型的超級病毒。如果一種疾病即將毀滅人類，只有少數具有免疫能力的人能夠倖免於難。幸運的是，我們知道某類人確實能夠抵禦特殊疾病。

Take HIV, for example. Some people have a genetic mutation that disables their copy of the CCR5 protein. HIV uses that protein as a doorway into human cells. So, if a person lacks CCR5, HIV can't enter their cells, and they're extremely unlikely to become infected with the disease. That being said, scientists say that people with this mutation are resistant rather than immune to HIV. A few individuals without this protein have contracted and even died from AIDS. Apparently, some unusual types of HIV have figured out how to use proteins other than CCR5 to invade cells. This type of resourcefulness is why viruses are so s with two copies of the defective gene are most resistant to HIV. Currently, that includes only about 1 percent of Caucasians and is even more rare in other ethnicities.

就拿HIV來說，一些人發生基因突變，使他們喪失了複製CCR5蛋白的能力。CCR5蛋白是HIV進入人體細胞的門戶。因此，一個缺失CCR5的人，HIV便無法進入他的細胞內，從而使得他們避免遭受感染。話雖如此，不過科學家們還表示，發生這類基因突變的人只能夠抵抗HIV，而不是對其免疫。這也就是爲什麼有少數人儘管缺失此類蛋白，但依舊被感染甚至死於艾滋病。顯然，一些特殊的HIV想通了如何利用CCR5之外的蛋白入侵細胞。這種類型的智謀正是病毒何以可怖的原因。擁有兩對缺陷基因的人大多能夠抵禦HIV。目前，這種人在高加索人中所佔比例爲百分之一，在其他種族中比例更低。

ria Resistance

8.防止瘧疾

Those who have an especially high resistance to malaria are carriers of another deadly disease: sickle cell anemia. Of course, no one wants the ability to dodge malaria only to die prematurely from malformed blood cells, but there is one situation where having the sickle cell gene pays off. To understand how that works, we have to explore the basics of both diseases.

這些對瘧疾有超高抵禦能力的人同時也是另外一種致命疾病的攜帶者：鐮刀型紅血球疾病。當然，沒有人願意爲了避免瘧疾而擁有這種"能力"，因爲患此病的人最終平均壽命只有四十歲。爲了瞭解它們如何工作，我們得探究這兩種疾病的基本知識。

Malaria is a type of parasite carried by mosquitoes that can lead to death or at the very least make someone feel at death's door. Malaria does its dirty work by invading red blood cells and reproducing. After a couple days, new malaria parasites burst out of the inhabited blood cell, destroying it. They then invade other red blood cells. This cycle continues until the parasites are stopped through treatment, the body's defense mechanisms, or death. This process causes a loss of blood and weakens the lungs and liver. It also increases blood clotting, which can spark a coma or seizure. Sickle cell anemia causes changes in the shape and makeup of red blood cells, which makes it difficult for them to flow through the blood stream and deliver adequate levels of oxygen. However, because the blood cells are mutated, they confuse the malaria parasite, making it difficult for it to attach and infiltrate the blood cells. Consequently, those who have sickle cells are naturally protected against malaria. You can get the anti-malaria benefits without actually having sickle cells, so long as you're a carrier of the sickle cell gene. To get sickle cell anemia, a person has to inherit two copies of the mutated gene, one from each parent. If they only get one, they have enough abnormal hemoglobin to resist malaria yet will never develop full-fledged use of its strong protection against malaria, the sickle cell trait has become highly naturally selected in areas of the world where malaria is widespread, with as much 10–40 percent of people carrying the mutation.

瘧疾是一種通過蚊子傳播的寄生蟲傳染病，每年導致的死亡人數高達上百萬。瘧疾通過入侵紅血細胞，不斷繁殖。短短几天，新的瘧原蟲便在所寄生的血細胞中爆發，並破壞血細胞。接着入侵其他血細胞。這個過程只有在瘧原蟲死亡，或者被治療方法阻止、人體產生防禦機制時纔會停止。整個過程會導致大量的血虧損，肺和肝的功能也會遭到損傷。它還會增加血凝塊，導致昏迷不醒和癲癇。鐮刀型紅血球疾病會使紅血球改變形狀，失去攜氧能力。正因爲紅血球細胞產生了變異，從而能夠迷惑瘧原蟲，讓其連接、滲透紅細胞變得更爲困難。於是，這些患有鐮刀型紅血球疾病的人便能夠抵禦瘧疾。並不是非得擁有鐮刀型細胞才能防止瘧疾，事實上攜帶鐮刀型基因也能擁有此種功能。一個人只有從父母那獲得兩對突變基因纔會患有鐮刀型紅血球疾病，如果他只獲得了一對呢？這種情況下，他擁有的異常血紅蛋白既能夠防止瘧疾，同時也不會患上鐮刀型紅血球疾病。因爲具有極強的防禦瘧疾功效，鐮刀型細胞具有很高的地域選擇性，在瘧疾高發地區，約有10—40%的人攜帶這種突變基因。

rance For Coldness

7.耐寒能力

Inuits and other populations who live in intensely cold environments have adapted to an extreme way of life. Have these people simply learned how to survive in these environments, or are they somehow biologically different?

因紐特人及其他生活在酷寒環境之中的人們，需要適應一種極端的生活方式。這些人僅僅是簡單學習如何在此種環境中生存，還是他們在生理上出於某種原因而與衆不同？

Cold-dwellers have different physiological responses to low temperatures compared to those who live in milder environments. And it appears there might be at least a partial genetic component to these adaptations, because even if someone moves to a cold environment and lives there for decades, their bodies never quite reach the same level of adaptation as natives who have lived in the environment for generations. For instance, researchers have found that indigenous Siberians are better adapted to the cold even when compared to non-indigenous Russians living in the same le native to cold climates have higher basal metabolic rates (around 50 percent higher) than those accustomed to temperate climates. Also, they can maintain their body temperatures better without shivering and have relatively fewer sweat glands on the body and more on the face. In one study, researchers tested different races to see how their skin temperatures changed when exposed to cold. They found that Inuits were able to maintain the highest skin temperature of any group tested, followed by other Native e types of adaptations partly explain why aboriginal Australians can sleep on the ground during cold nights (without shelter or clothing) with no ill effects and why Inuits can live much of their lives in subzero human body is much better suited at adjusting to heat than to cold, so it's rather impressive that people manage to live at all in freezing temperatures, let alone thrive.

寒冷環境中的居住者相比較那些在溫暖環境居住的人們來說，對於低溫度的生理性反應有所不同。這種情況之所以發生，也許是爲了適應環境而發生了一小部分遺傳成分的改變。因爲，即使是移居至寒冷生活環境中居住數載的人，他們身體的適應性水平，依然無法等同於那些在本環境中居住數代的人們。例如，調查者發現，雖然生活在同一個羣落，但土著西伯利亞人較之非本地的俄羅斯人來說，對於寒冷的適應能力更強。土生土長於寒冷環境中的人們，比那些習慣了溫帶氣候的人們，擁有更高的基礎代謝率（大概高於百分之五十）。而且，他們能夠更好的維持體溫而不至於打寒戰，並可以在身體上擁有相對少的汗腺，而在臉上擁有的更多。在一項研究中，調查者們測試了不同種族的人們，去觀察當他們的皮膚暴露於寒冷中時，其表面溫度是如何變化的。調查者發現，因紐特人在所測試的所有種族的人羣中，其皮膚可以保持最高的溫度，緊接着是其他本土美國人。這些類型的適應性，部分程度上解釋了爲什麼澳大利亞土著人可以在寒冷的晚上睡在地面上（沒有遮蔽物或者衣服），也不至於生病，並說明了爲什麼因紐特人大部分的生活都是居住在零度以下的環境。人體在調整熱的方面比調整冷更加擅長，所以，令人印象十分深刻的是，人們都設法居住在寒冷的溫度中，獨自成長壯大。

mized For High Altitude

6.更適應高海拔環境

Most climbers who've made it to the summit of Mt. Everest wouldn't have done so without a local Sherpa guide. Amazingly, Sherpas often travel ahead of the adventurers to set ropes and ladders, just so the other climbers have a chance of making it up the steep cliffs.

如果沒有當地夏爾巴人作爲嚮導，很多人將無法成功登頂珠穆朗瑪峯。夏爾巴人經常走在冒險者前面，爲他們設置繩索和梯子，只有這樣，這些攀登者纔有機會登上陡峭的懸崖。

There's little doubt that Tibetans and Nepalese are physically superior in this high-altitude environment, yet what is it exactly that allows them to work vigorously in oxygen-depleted conditions, while ordinary folks have to struggle just to stay alive?Tibetans live at an altitude above 4,000 meters (13,000 ft) and are accustomed to breathing air that contains about 40 percent less oxygen than at sea level. Over the centuries, their bodies compensated for this low-oxygen environment by developing bigger chests and greater lung capacities, which make it possible for them to inhale more air with each breath. And, unlike lowlanders whose bodies produce more red blood cells when in low oxygen, high-altitude people have evolved to do the exact opposite—they produce fewer red blood cells. This is because while an increase in red blood cells might temporarily help a person get more oxygen to the body, it makes blood thicker over time and can lead to blood clots and other potentially deadly complications. Similarly, Sherpas have better blood flow in their brains and are overall less susceptible to altitude when living at lower altitudes, Tibetans still maintain these traits, and researchers have found that many of these adaptations aren't simply phenotypic variances but are genetic adaptations. One particular genetic change occurred in a stretch of DNA known as EPAS1, which codes for a regulatory protein. This protein detects oxygen and controls production of red blood cells and explains why Tibetans don't overproduce red blood cells when deprived of oxygen, like ordinary Han Chinese, the lowland relatives of the Tibetans, do not share these genetic characteristics. The two groups split from each other about 3,000 years ago, which means these adaptations occurred in only about 100 generations—a relatively short time in terms of evolution.

毋庸置疑，藏族人和尼泊爾人在高海拔環境下身體十分出衆。那麼，到底是什麼使得他們在如此缺氧的環境下精力如此旺盛？要知道，普通人在這種環境下只有喘氣的分。藏人生活在4000米高的海拔，常年呼吸着氧含量比海平面約少40%的空氣。幾個世紀以來，他們的身體發展出寬大的胸腔，擁有更大的肺容量作爲補償。這讓他們每次呼吸都能夠吸入更多的空氣。與居住在低海拔的人不同，低海拔地區的人身處低氧環境時身體會製造更多的紅血細胞，而高海拔地區的人則進化出截然相反的功能：他們產生更少的紅細胞。這是因爲紅細胞的增加只會暫時幫助身體獲取更多的氧氣，但是隨着時間的推移，卻會導致血液變厚，產生血凝塊，以及其他致命的併發症。相似的，夏爾巴人大腦的血流量更好，這使得他們整體不易產生高原反應。當藏人居住在低海拔地區時，他們仍然保持着這種特徵。研究人員發現，這種變化並不是簡單的表面型改變，而是遺傳性適應。一個特定的基因變化發生在一段名爲EPAS1的DNA上，其編碼調節蛋白質。這種蛋白質檢測氧氣並控制紅血細胞的生產量。這就解釋了爲什麼當藏族人身處缺氧環境時不會像正常人那樣製造更多的紅血細胞。生活在低海拔地區的漢人雖然是藏族人的親屬，卻並沒有這種基因特徵。漢人和藏人大約在3000年前分開，這就意味着這種改變的發生僅僅只有100代人的時間——屬於進化中時間較短的情況。

翻譯：煙囪、徐杉、歐陽遠麗、阿飯、孟慶潤 來源：前十網