Write your answer in about 150 words for each of the following : 10×5=50 (a) Describe the requirement of proteins for the…

(a) Protein Requirements for Eukaryotic Transcription Initiation

Eukaryotic transcription initiation requires the coordinated assembly of RNA Polymerase II, General Transcription Factors (GTFs), and accessory co-activator complexes onto core promoter elements, including the TATA box, Initiator (Inr), and Downstream Promoter Element (DPE). Initiation begins when transcription factor TFIID, via its TATA-Binding Protein (TBP) subunit and TBP-Associated Factors (TAFs), binds specifically to the TATA box. TFIIA subsequently binds to stabilize the TFIID-DNA complex, while TFIIB recognizes the B recognition element (BRE) and acts as a molecular bridge between TFIID and RNA Polymerase II. TFIIF escorts RNA Polymerase II to the promoter, ensuring its precise positioning over the transcription start site. TFIIE then joins the assembly to recruit TFIIH, completing the Pre-Initiation Complex (PIC). TFIIH exerts ATP-dependent helicase activity to unwind the double helix, forming the open promoter complex, while its cyclin-dependent kinase subunit phosphorylates the C-terminal domain (CTD) of RNA Polymerase II at Serine-5 residues to facilitate promoter clearance. Gene-specific transcriptional activators and the multi-protein Mediator co-activator complex further stimulate PIC assembly and transition to elongation.

(b) Modern Concept of Gene and Test of Allelism

The modern concept of the gene departs from the classical bead-on-a-string hypothesis, defining the gene as a complex transcriptional and operational unit of heredity consisting of coding exons interrupted by non-coding introns (split genes). Genes can overlap to maximize genome economy, generate multiple protein isoforms via alternative splicing, and encode functional non-coding RNAs. Seymour Benzer redefined the gene into functional operational units: the cistron (unit of function), muton (smallest unit of mutation), and recon (smallest unit of recombination).

The test of allelism, or cis-trans complementation test developed by Benzer using the rII locus of bacteriophage T4, determines whether two independent recessive mutations occur within the same cistron or in separate cistrons. When two mutant genomes are introduced into Escherichia coli K12 in the *trans*-configuration (m₁ + / + m₂), complementation occurs if each mutant chromosome supplies a functional product missing in the other, resulting in wild-type lysis. This proves the mutations reside in different cistrons (rIIA and rIIB). If no lysis occurs, both mutations affect the same cistron and are allelic. The *cis*-configuration (m₁ m₂ / + +) always yields a wild-type phenotype, serving as an internal positive control.

(c) Mimicry: Definition and Types

Mimicry is the close morphological, behavioural, or physiological resemblance of one organism (the mimic) to another organism (the model) or an inanimate object, providing an evolutionary survival advantage against predation or foraging constraints.

Batesian mimicry involves an edible, palatable mimic resembling an unpalatable, toxic model to deter shared predators. In India, the palatable female Papilio polytes (Common Mormon butterfly) exhibits polymorphism, mimicking unpalatable models such as Pachliopta aristolochiae (Common Rose).

Müllerian mimicry occurs when two or more distinct unpalatable or defended species evolve convergent warning colouration (aposematism), thereby sharing the mortality cost of predator learning. Classic examples include the co-mimetic warning patterns of Danaine butterflies, such as Danaus chrysippus (Plain Tiger) and Euploea core (Common Indian Crow).

Aggressive mimicry involves predators or parasites mimicking harmless models or alluring cues to facilitate predation or host exploitation, as observed in the anglerfish (Lophius), which utilizes a modified dorsal fin spine (illicium) resembling prey.

Automimicry occurs when an organism mimics parts of its own body, such as false eyespots on the posterior wings of lycaenid butterflies, or when palatable individuals of a species chemically mimic defended conspecifics.

(d) Use of Molecular Techniques in Animal Taxonomy

Molecular techniques provide objective, discrete, and quantifiable characters to delimit taxa, reconstruct evolutionary phylogenies, and uncover cryptic biodiversity. DNA barcoding employs a standardized 648-base-pair region of the mitochondrial Cytochrome c Oxidase subunit I (COI) gene for rapid species-level identification and discrimination of cryptic sibling species, a protocol widely applied in Indian faunal surveys by the Zoological Survey of India. Restriction Fragment Length Polymorphism (RFLP) and DNA-DNA hybridization assess sequence divergence and overall genomic homology across species. Polymerase chain reaction (PCR)-based markers, including Random Amplified Polymorphic DNA (RAPD) and Amplified Fragment Length Polymorphism (AFLP), detect genetic polymorphism across populations. Variable number tandem repeats, such as microsatellites (SSRs) and Single Nucleotide Polymorphism (SNP) genotyping, resolve fine-scale phylogeography and hybridization boundaries. Furthermore, sequencing of nuclear ribosomal genes (18S and 28S rDNA) alongside mitochondrial markers (16S rRNA and Cytochrome b) enables multi-locus phylogenetic reconstruction, resolving deep evolutionary relationships and species complexes where morphological characters exhibit evolutionary homoplasy.

(e) Cladistics and the International Code of Zoological Nomenclature

Cladistics, or phylogenetic systematics, is an evolutionary classification framework based on shared derived character states (synapomorphies) to reconstruct natural monophyletic lineages, comprising an ancestor and all its descendants. Unlike phenetics based on overall similarity or evolutionary systematics that permits paraphyly, cladistics strictly utilizes derived characters to generate hierarchical branching diagrams known as cladograms, while excluding shared ancestral traits (symplesiomorphies).

The International Code of Zoological Nomenclature (ICZN) establishes the formal rules governing the naming of animal taxa: Binomial nomenclature mandates that every species name consists of a Latinized binomen, comprising a capitalized genus name and a lowercase specific epithet (e.g., Panthera tigris). The Principle of Priority dictates that the oldest validly published name applied to a taxon, starting from Linnaeus's Systema Naturae (10th edition, 1758), takes precedence. The Principle of Typification requires that every nominal taxon be permanently anchored to an objective type specimen (such as a holotype or lectotype) deposited in an accessible public museum or scientific repository. Publication criteria mandate distribution in permanent, widely accessible scientific media, complete with Latinized grammatical consistency and diagnostic descriptions. Higher-taxon nomenclature enforces standardized suffixes to define rank, notably -idae for families and -inae for subfamilies.