The concept of 'survival of the fittest' was proposed by: MCQ with Answer and Explanation

Explanation:
Polymerase chain reaction (PCR) amplifies a specific DNA segment exponentially using primers, DNA polymerase (Taq), and thermal cycling. Gel electrophoresis separates DNA by size, sequencing determines base order, microarray analyzes gene expression. PCR is crucial in cloning, diagnostics, and forensics.

Explanation:
The TATA box (consensus sequence TATAAA) is a highly conserved DNA sequence located about 25-30 base pairs upstream of the transcription start site in the promoter region of many eukaryotic genes transcribed by RNA polymerase II. It is specifically recognized and bound by the TATA-binding protein (TBP), which is a crucial subunit of the general transcription factor TFIID. The binding of TBP initiates the assembly of the pre-initiation complex, including RNA polymerase II, allowing transcription to begin.

Explanation:
Chief cells (peptic cells) in the gastric mucosa secrete pepsinogen, which is converted to active pepsin by HCl. Pepsin digests proteins into peptides. Parietal cells secrete HCl and intrinsic factor. Mucous cells produce mucus that protects the stomach lining. G cells secrete gastrin hormone. Pepsin functions optimally at pH 1.8-2.0. The stomach thus initiates protein digestion.