突变（mutation)

倒位突变(inverse mutation)

缺失突变(deletion mutation)

同义突变(synonymous mutation)

框移突变(frame-shift mutation)

根据材料请回答 31～35

Natural Selection

Natural selection describes the biological process in which the differences of individu-als within a population influence their abilities to survive and reproduce in an environment.The differences in individuals are a result of their genetic inheritance from their parents.In a population, any characteristic which blocks reproduction tends to decrease generation by generation.In time, the ill-adapted die out.On the other hand, the individuals who do survive and reproduce will tend to produce offspring(后代which are better adapted to the environment.Natural selection tends to promote adaptations that will increase the organ- ism's(生物体)ability to survive in an environment.

Natural selection can serve to stabilize a population if the new traits, called mutations (突变), are eliminated when they appear because they are not as well-adapted to the envi-ronment.The opposite effect is' obtained when a new trait is introduced which allows indi-viduals to adapt better over time, the species will change as this mutation becomes more widespread in the population.In human beings, increased brain size helped individuals to adapt better; and so brain size increased gradually in the species.Changes in the overall genetic makeup of a population are normal when there are environmental changes, espe-cially severe environmental disruptions.Specialized adaptations to specific environments can lead, over time, to the development of subpopulation of individuals, who are better a- dapted to particular soil conditions, food sources and so on.Given enough time, these subpopulations may develop into separate species, such as zebras(斑马)and horses, living in distinct environments and not interbreeding.

第 31 题 Individuals in a population differ from one another because__________.

A．they have different success generation by generation

B．they are ill-adapted and eventually die out

C．they have different genetic inheritances

D．they want to survive and reproduce successfully

A.同义突变

B.非同义突变

C.移码突变

D.点突变