Book 1 Reading and Speaking (1108795), страница 13
Текст из файла (страница 13)
Type 2 diabetes strikes Latin Americans and people of African descent more often than it does thoseof other ethnic groups, appearing at rates of incidence that are 90 and 60 percent higher, respectively, than inCaucasians. Researchers have been conducting studies such as the International HapMap Project--a global effortto catalogue common single-nucleotide variations, such as the addition, deletion or substitution of a base in thecode of a gene--to get to the bottom of long-observed correlations between ethnicity and common complexdiseases.But those efforts have borne little fruit, according to Vivian Cheung, a human geneticist at the University ofPennsylvania School of Medicine.
So, rather than characterize these individual nucleotide changes in genes,Cheung and geneticist Richard Spielman employed microarray technology--essentially a genome chip that allows aresearcher to analyze the expression of many genes at once--to study across Chinese, Japanese and Europeanpopulations many different traits that are coded for in a type of white blood cell.Their results, reported in this week's Nature Genetics, were that different ethnic groups not only carrieddifferent genes, but there were greater disparities than previously believed in the degrees to which genes that werethe same among ethnic groups were expressed. Further, the genes themselves did not control the levels of theirown expression, rather noncoding regions adjacent to them determined whether to ratchet up or down the proteinsor other functional end products the genes encoded.The authors of the new study note that large-scale changes to DNA--such as specific substitutions ordeletions of genetic material--almost certainly also contribute to differences between ethnic groups.
But Cheungsays that expression levels likely can explain some of the ethnic underpinnings of Tay-Sachs and cystic fibrosis aswell as hypertension, which plagues those of Afro-Caribbean descent at a higher rate than other populations.From its microarray, the team measured 4,197 genes expressed by cells. (After measuring expression levelsof those genes, Cheung, Spielman and their colleagues decided to lump the Japanese and Chinese groupstogether due to similar results.) When the researchers then compared the Asian populations with the Caucasiansampling, they noted that 1,097, more than 25 percent, of the genes had differing expression levels.After analyzing some of the nearly 1,100 genes in detail, Cheung and Spielman believe that the expressionlevel discrepancies were due to nucleotide differences in noncoding regions around the genes, and not the genesthemselves.
"We were able to pinpoint 11 genes where people have different forms of the regulator," Cheungreveals, providing an example: "Let's say that among the Caucasian population, maybe the regulator that turns onthe gene more happens to be more frequent--overall the expression level of that gene will be higher. Whereas inthe Asian population, more people have the regulator that causes the expression level to be lower."Steve McCarroll, a population and medical geneticist at the Massachusetts Institute of Technology's BroadInstitute says that with so many genetic variants out there, researchers need all the help they can get determiningwhich ones actually will affect cell function.
"One of the things that's exciting about this work is that identifying thegenetic variants that account for gene expression differences could help the field to find those genetic variants thataffect disease risk," he says. (From Scientific American Online, January 9, 2007)Exercise 4. Who are the following scientists mentioned in the articles? What studies have they carried out?• Kari Stefansson• George Coop• Vivian Cheung and Richard Spielman• Steve McCarrollExercise 5. Using the information from the texts prove that:1. DNA recombination is the source of variation in populations.322.3.4.5.DNA recombination is age and sex related.Ethnic groups suffer from particular common diseases.Not only different genes but difference in expression levels of these genes account for common diseases.Noncoding regions are responsible for the degree of gene expression.Exercise 6.
Put the sentences given below (a-e) into their correct place in the text (1-5).Ancient Europeans More Diverse, Genetically Speaking, than Modern OnesBubonic plague may be responsible for reducing the genetic diversity of present-day BritonsBy David BielloModern Britons are a cosmopolitan bunch. Peoples from across the globe now make the island home,bringing with them, theoretically, a diverse array of genes.
(1) _____ Molecular ecologist Rus Hoelzel of DurhamUniversity in England and his European colleagues compared the genetic make up of six English ancestors fromthe Roman period, 25 from early in the Saxon conquest and 17 from the late Saxon period with the mitochondrialDNA sequences of more than 6,000 modern Europeans and Middle Easterners.
"We found higher mitochondrialDNA diversity in ancient England (Roman to Saxon times) than in either modern England or in a combination ofnorthern European countries," Hoelzel says. (2) _______Even when present-day Europeans were broken down into 10 smaller samples of 48 individuals each, theystill were less diverse than their ancestors. (3) ______ ; 6.3 percent of ancients carried it compared with nearly 22percent of modern Britons and an average of nearly 19 percent of all Europeans.The CRS haplotype imparts no known special traits in the humans who bear it, but the "black death" mayhave played a role in increasing its abundance in the modern population.
(4) _____ The dread disease could eitherhave increased the proportion of certain haplotypes somehow associated with increased survival or simply led tothe extinction of rare haplotypes in families or villages who had a particular susceptibility, Hoelzel says.Only three small groups—modern peoples from Belarus, Palestine and Turkey—showed similar levels ofdiversity to these early ancestors, though studies by others have shown that southern Europeans, such as Italians,seem to retain a broader pool of genetic material.
(5) ______ , according to researchers, the ancients possessed amore robust array of differing genetic stocks. (From Scientific American Online, August 1, 2007)(a) The 48 ancients bore 36 different haplotypes—a set of variations in the genetic code. But theirdescendants more commonly carried one particular haplotype, known as Cambridge referencesequence (CRS)(b) It is unclear exactly why contemporary Europeans are less genetically diverse despite a continuing influxof new populations but,(c) This bubonic plague swept Britain (and all of Europe) in the 14th century, killing as much as half of thepopulation, before recurring again in London in the 17th century.(d) “Modern human populations are highly diverse, just less so in northern Europe, at least, than the ancientpopulations in England."(e) But comparing the genetic material of more than 1,000 contemporary Englishmen with that of 48 of theirancient peers reveals that the ancients had even more diverse genetic codes.Exercise 7.
In the following text the lines are mixed up. Put them in the correct order.Genetic Study Reveals Similarities between Diverse PopulationsBy Sarah Grahamgenetically very similar, researchers say. A report published today in the journal Science suggests that 93 to 95from differences in a very small proportion of genetic traits."people from several continents, suggesting that only a tiny fraction of genetic traits are distinctive to specificpercent of human genetic variation exists among individuals within populations, while differences among majorMarcus W.
Feldman of Stanford University and his colleagues analyzed samples from 1,056 people belonging toalone can provide enough information to group people by population.52 populations. Specifically, they looked at 377 so-called microsatellites, short segments of DNA that occur inThough they may speak different languages and eat distinct foods, people from far-flung geographical locations arepopulations. This means that visible differences between human groups--such as skin color and skull shape--resultgroups make up less than 5 percent of the variation. But the findings also reveal that even these tiny differencesspecific patterns. "Each microsatellite had between four and 32 distinct types," Feldman says.
"Most were found in(From Scientific American Online, December 20, 2002)Exercise 8. Summarize everything you know about population diversity and genetic mechanisms involvedinto one report.33Unit 10. Animal DiversityNature proceeds little by little from thingslifeless to animal life in such a way that it isimpossible to determine the exact line ofdemarcation, nor on which side thereof anintermediate form should lie.AristotleExercise 1. What do you know about diversity of animals and their adaptations?1. Why are animals classified into a separate Kingdom?2.
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