2014年6月大学英语四级冲刺试题及答案(第三套)_第6页

　　Questions 26 to 30 are based on the following passage.

　　We all know that DNA has the ability to identify individuals but, because it is inherited, there are also regions of the DNA strand which can relate an individual to his or her family (immediate and extended), tribal group and even an entire population. Molecular Genealogy (宗谱学) can use this unique identification provided by the genetic markers to link people together into family trees. Pedigrees (家谱) based on such genetic markers can mean a breakthrough for family trees where information is incomplete or missing due to adoption, illegitimacy or lack of records. There are many communities and populations which have lost precious records due to tragic events such as the fire in the Irish courts during Civil War in 1921 or American slaves for whom many records were never kept in the first place.

　　The main objective of the Molecular Genealogy Research Group is to build a database containing over 100,000 DNA samples from individuals all over the world. These individuals will have provided a pedigree chart of at least four generations and a small blood sample. Once the database has enough samples to represent the world genetic make-up, it will eventually help in solving many issues regarding genealogies that could not be done by relying only on traditional written records. Theoretically, any individual will someday be able to trace his or her family origins through this database.

　　In the meantime, as the database is being created, molecular genealogy can already verify possible or suspected relationships between individuals. “For example, if two men sharing the same last name believe that they are related, but no written record proves this relationship, we can verify this possibility by collecting a sample of DNA from both and looking for common markers (in this case we can look primarily at the Y chromosome (染色体)),” explains Ugo A. Perego, a member of the BYU Molecular Genealogy research team.

　　26. People in a large area may possess the same DNA thread because .

　　A) DNA is characteristic of a region

　　B) they are beyond doubt of common ancestry

　　C) DNA strand has the ability to identify individuals

　　D) their unique identification can be provided via DNA

　　27. The possible research of family trees is based on the fact that .

　　A) genetics has achieved a breakthrough

　　B) genetic information contained in DNA can be revealed now

　　C) each individual carries a unique record of who he is and how he is related to others

　　D) we can use DNA to prove how distant an individual is to a family, a group or a population

　　28. The Molecular Genealogy Research Group is building a database for the purpose of .

　　A) offering assistance in working out genealogy-related problems

　　B) solving many issues without relying on traditional written records

　　C) providing a pedigree chart of at least four generations in the world

　　D) confirming the assumption that all individuals are of the same origin

　　29. If two men suspected for some reason they have a common ancestor, .

　　A) we can decide according to their family tree

　　B) we can find the truth from their genetic markers

　　C) we can compare the differences in their Y chromosome

　　D) we can look for written records to prove their relationship

　　30. Which of the following CANNOT be inferred from the passage?

　　A) We are a walking,living,breathing record of our ancestors

　　B) Many American slaves did not know who their ancestors were.

　　C) An adopted child generally lacks enough information to prove his identity.

　　D) Molecular genealogy can be used to prove a relationship between individuals.