Which of the following statements are incorrect?

(A) Fragments of DNA can be separated by ELISA.
(B) Transformation is a procedure through which a piece of DNA is introduced in a host bacterium.
(C) Recombinant DNA technology does not involve isolation of a desired DNA fragment.
(D) DNA ligases are used for stitching DNA fragments into a vector.

Choose the answer from the options given below:

The correct answer is (A) and (C) only.

Let us analyze each statement step-by-step to understand why statements (A) and (C) are incorrect, while (B) and (D) are correct:

Statement (A): "Fragments of DNA can be separated by ELISA."
This statement is incorrect. ELISA (Enzyme-Linked Immunosorbent Assay) is a wet-lab technique used to detect and quantify substances such as proteins, antibodies, and hormones in a sample. It is not used for separating DNA fragments. Instead, fragments of DNA are separated based on their size using a technique called agarose gel electrophoresis.

Statement (B): "Transformation is a procedure through which a piece of DNA is introduced in a host bacterium."
This statement is correct. Transformation is a key process in genetic engineering where host cells (such as bacteria) take up foreign DNA from their surroundings and incorporate it into their own genome or maintain it as a plasmid.

Statement (C): "Recombinant DNA technology does not involve isolation of a desired DNA fragment."
This statement is incorrect. Recombinant DNA technology absolutely requires the isolation of a desired DNA fragment (gene of interest) as its very first step. Without isolating the target DNA sequence, it cannot be cloned, joined to a vector, or expressed in a host organism.

Statement (D): "DNA ligases are used for stitching DNA fragments into a vector."
This statement is correct. DNA ligases are molecular glue enzymes that facilitate the joining of DNA strands together by catalyzing the formation of a phosphodiester bond, which is essential for inserting a desired DNA fragment into a vector plasmid.

Since the question asks for the incorrect statements, statements (A) and (C) fit the criteria, making (A) and (C) only the correct choice.