Assertion (A): Genetic variation is essential for evolution. Reason (R): Without variation, natural selection cannot occur because there are no differences to select from. MCQ with Answer and Explanation

Explanation:
Restriction endonucleases are molecular scissors that recognize and cut DNA at specific, highly specific palindromic nucleotide sequences, creating fragments with sticky or blunt ends. DNA ligase is an enzyme that catalyzes the formation of phosphodiester bonds between adjacent DNA fragments, effectively joining or 'pasting' them together, crucial in recombinant DNA technology. PCR (Polymerase Chain Reaction) is used to exponentially amplify specific DNA segments, not to sequence them; DNA sequencing is a separate technique. Thus, statements 1 and 2 are correct.

Explanation:
Kidneys filter blood (1) and produce erythropoietin (3). Glucose reabsorption occurs in the proximal tubule, not collecting duct. So 2 is incorrect.

Explanation:
Diphtheria affects the throat, forming a pseudomembrane, and releases a toxin affecting the heart and nerves. Tetanus is Clostridium, pertussis Bordetella, typhoid Salmonella.