The incorrect statement related to gel electrophoresis is Option A: Separated DNA fragments can be directly seen under UV radiation.

Here's why:

DNA itself is not fluorescent. To visualize DNA fragments after separation, a dye that binds to DNA and fluoresces under UV light is used. This dye, often ethidium bromide or SYBR Safe, intercalates between the DNA bases, making the DNA visible under UV light.

Let's look at the other options:

Option B: Separated DNA can be extracted from gel piece is correct. DNA fragments can be extracted from the gel by cutting out the desired band and using a method called gel extraction. This allows for further analysis or cloning of the extracted DNA.

Option C: Fragment of DNA moves toward anode is also correct. DNA molecules carry a negative charge due to the phosphate groups in their backbone. In gel electrophoresis, the DNA is loaded into wells at the negative end of the gel. When an electric current is applied, the negatively charged DNA fragments migrate towards the positive electrode (anode).

Option D: Sieving effect of agarose gel helps in separation of DNA fragments is correct. Agarose gel acts as a sieve, with pores that allow smaller fragments to travel through more easily than larger fragments. This difference in mobility, based on size, allows for separation of DNA fragments.