Final Answer:
Cosmids can take up large DNA fragments because they possess features of both plasmids and bacteriophages, combining the circular stability of plasmids with the packaging efficiency of bacteriophages.
Step-by-step explanation:
Cosmids are hybrid vectors engineered for genetic engineering purposes. They incorporate features from both plasmids and bacteriophages. The circular structure of plasmids provides stability and the ability to replicate within a bacterial cell.
However, cosmids also carry elements of bacteriophages, such as the packaging site, allowing them to be efficiently packaged into viral particles during the formation of phage particles. This feature enables cosmids to accommodate larger DNA fragments than traditional plasmids.
As a result, cosmids serve as valuable tools in molecular biology and genetic engineering, facilitating the cloning and manipulation of large genomic DNA fragments in various research applications.