In DNA transfer the vectors used from smallest to largest is
**Core Concept**
The question is testing the student's knowledge of the different types of vectors used in DNA transfer, specifically their sizes. DNA transfer is a process of introducing genetic material into a cell, and vectors are the tools used for this purpose. The vectors are classified based on their size, from smallest to largest.
**Why the Correct Answer is Right**
The correct answer is **plasmid**, followed by **bacteriophage**, and then **cosmid**. Plasmids are small, self-replicating circular DNA molecules found in bacteria, typically ranging from 1 to 10 kilobases (kb) in size. They are the smallest vectors used in DNA transfer. Bacteriophages, or simply phages, are viruses that infect bacteria and can be used as vectors for DNA transfer, with sizes ranging from 10 to 100 kb. Cosmids are hybrid vectors that combine the features of plasmids and bacteriophages, with sizes ranging from 30 to 40 kb. They are used for cloning larger DNA fragments.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, but the correct sequence is plasmid, bacteriophage, and cosmid.
* **Option B:** This option is not provided, but the correct sequence is plasmid, bacteriophage, and cosmid.
* **Option C:** This option is not provided, but the correct sequence is plasmid, bacteriophage, and cosmid.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the choice of vector depends on the size of the DNA fragment to be cloned. Plasmids are ideal for small fragments, while bacteriophages and cosmids are used for larger fragments.
**Correct Answer: D. Cosmid. Cosmids are hybrid vectors that combine the features of plasmids and bacteriophages, with sizes ranging from 30 to 40 kb.**