课件21张PPT。Unit 2 Cloning Section Ⅰ Warming Up & Reading — Pre-readingStep 1Step 2Step 3Step 4Step 51．What are the advantages and disadvantages of cloning? 2．Not only animals but also plants can be cloned. Do you know the difference between them? Please read the following passage to get the answer. A new study of plants that are reproduced by cloning has shown why cloned plants are not identical. Scientists have known for some time that cloned organisms are not always identical: their observable characteristics and traits can vary, and this variation can be passed on to the next generation. This is despite the fact that they are derived (获得) from genetically identical founder cells. Now, a team from Oxford University, the UK, and King Abdullah University of Science and Technology, Saudi Arabia, believe they have found out why this is the case in plants: the genomes (染色体) of regenerate plants carry relatively high frequencies of new DNA sequence mutations (变异) that were not present in the genome of the donor plant. The team reported their findings in this week's Current Biology. “Where these new mutations actually come from is still a mystery，” said Professor Harberd. “They may arise during the regeneration process itself or during the cell divisions in the donor plant that gave rise to the root cells from which the regenerate plants are created. We are planning further research to find out which of these two processes is responsible for these mutations. What we can say is that nature has safely been employing what you might call a ‘cloning’process in plants for millions of years, and that there must be good evolutionary reasons why these mutations are introduced.” The new results suggest that variation in clones of plants may have different underlying causes from those of variation in clones of animals － where it is believed that the effect of environmental factors on how animal genes are expressed is more important and no similar high frequencies of mutations have been observed. Professor Harberd said, “While our results highlight that cloned plants and animals are very different, they may give us insights into how bacterial and cancer cells replicate themselves, and how mutations arise during these processes which, ultimately, have an impact on human health.”1．How much do you know about clone? What is clone? And what are natural clone and man-made clone? _____ _____ 答案：Clone is a way of making an exact copy of another animal or plant. Natural clone is one that occurs from the “parent” in a natural form of cloning without human help. Man-made clone is one produced through human intervention (介入)．2．Look at these pictures and tell which ones are natural clones and which ones are man-made._____ 答案：Natural clones：A, F；Man-made clones：B，C，D, E3．See another kind of clone. The two women soldiers look very alike. Can you explain why?_____ 答案：They are called twins. They were born almost at the same time by t ... ...
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