生物的一生好像是一场忙忙碌碌的建设工程，按照基因的图纸，一步一步地向终点迈进。在需要某种产品时，相应的基因就会被调用出来，当生产完毕后，这张图纸又会暂时或者永久搁置起来。但是有一些基因，它们在某类生物的一生中都不会用到，而在另一类生物中却会被尽情使用。这 The life of a creature seems to be a busy construction project, and it is step by step to the end point according to the drawings of the genes. When a certain product is needed, the corresponding gene will be called out. When the production is completed, this drawing will be temporarily or permanently set aside. But there are some genes that will not be used in the life of a certain type of organism but will be used in other types of organisms. This