Câu hỏi:

Read the following passage and mark the letter A,B,C or D on your answer sheet to indicate the correct answer to each of the questions from 55 to 64

Genetics is the study of hereditary characteristics that are passed down from one generation of living organisms to another. Although farmers have used selective breeding to improve the resilience of crops and animals, it wasn't until the mid 1800s that Gregor Mendel started the science of genetics as we know it today. Following Mendel's methods, scientists have discovered "chromosomes" and "DNA". With the ability to study DNA, scientists were ableto study the genetic differences between races.

Modern genetics discovered that all humans are descendants of "Mitochondrial Eve," a woman who lived over 150,000 years ago in Africa. Since the first humans were born, over 75,000 generations have passed, and many subtle differences are now evident. Humans share at least 99% of their genetic makeup. A 1% difference may not seem like much, but when you consider that a chimpanzee shares 98% of human genes, you realize how much a 1% difference makes!

Africans are more closely related to Europeans than any other two groups, despite the fact that they differ so much in appearance. The biggest genetic differences are found between Africans and the native populations of NorthAmerica (22%). However, it is essential to note that the genetic differences between people of the same race are much greater than the differences between people of different races. This means that the argument which claims that genetic differences make one race superior to another is nothing but a tall story.

The differences in various populations may also be the result of circumstances rather than genetic makeup. Factors such as climate, diet, health care, education, and employment as well as other socioeconomic factors are all influential. However, there are some traits which are genetic; for example, there is a much higher incidence of sickle-cell anemia among black populations than any other population group. Adult African-Americans and Latinos have twice as many cases of diabetes than Caucasians. In the U.S., Latinos suffer more deaths from liver disease than other races. Europeans suffer more from heart disease and cancer.

Genes not only affect our susceptibility to disease, they also affect our physical attributes. The Dinka people from the Sudan are considered to be the tallest people with men having an average height of 6ft 3in., while women hit the big time with an impressive 5ft 3in. This contrasts sharply with the Pygmy tribes who get the short end of the stick at only about 4ft 11in.tall. Genetic differences may help us to tailor health services to people of different races or to detect life threatening diseases early. However, they are not significant enough to support the claim that one race is superior toanother. In fact, our modern scientific understanding of human genetic diversity flies in the face of almost all our social stereotypes

Where do the greatest genetic differences occur?