A pure sample of DNA or RNA is the starting point for many molecular biology applications. A few examples for each are listed here.

Applications that require purified DNA as a starting point:
>Genetic Sequencing (e.g., whole genome, exome, targeted sequencing)
>PCR (Polymerase Chain Reaction) for gene amplification
>Cloning and Recombinant DNA Technology
>Gene Editing (e.g., CRISPR/Cas9)
>DNA Methylation Analysis (e.g., bisulfite sequencing)
>Southern Blotting for DNA detection
>DNA Microarray Analysis for gene expression profiling
>Gene Synthesis and vector construction
>Forensic DNA Profiling
>Genotyping and SNP Analysis
>In vitro Transcription for RNA synthesis from DNA
>DNA-based Vaccines development
>Phylogenetic Studies for evolutionary analysis
>Metagenomic Studies for analyzing environmental DNA (eDNA)
>DNA Storage and Computing (e.g., DNA data storage)
>Gene Therapy Research
>Synthetic Biology Applications
>Mutation Detection and molecular diagnostics (e.g., for cancer)
>Protein Expression Studies (e.g., using plasmids in bacterial systems)
>Agricultural Biotechnology (e.g., transgenic plant development)

Applications that require purified RNA as a starting point:
>cDNA Synthesis for reverse transcription into DNA (RT-PCR)
>RNA Sequencing (RNA-Seq) for transcriptome analysis
>Quantitative RT-PCR (qRT-PCR) for gene expression analysis
>Microarray Analysis of gene expression
>RNA Interference (RNAi) for gene silencing
>CRISPR-Cas13 applications for RNA targeting
>In vitro Translation for protein synthesis from RNA templates
>mRNA Vaccine Development (e.g., COVID-19 vaccines)
>Northern Blotting for RNA detection
>RNA Methylation and Modification Studies (e.g., m6A RNA modifications)
>siRNA/shRNA Design for gene knockdown experiments
>RNA Structural Analysis (e.g., RNA folding studies)
>RNA Stability and Decay Assays
>Single-cell RNA Sequencing (scRNA-seq) for analyzing gene expression at the single-cell level
>MicroRNA (miRNA) Profiling for regulatory RNA studies
>RNA Aptamer Selection for developing RNA-based biosensors
>Ribosome Profiling to study translation in cells
>Long Non-coding RNA (lncRNA) Studies for gene regulation research
>Viral RNA Detection and Characterization (e.g., for identifying RNA viruses)
>RNA-based Therapeutics Research (e.g., antisense oligonucleotides)