Functional and Comparative Genomics

Once a genome is sequenced the harder questions begin: which stretches are functional, what do they do, and what can be learned by comparing the genome with those of other species.

Definition

Functional genomics seeks to assign biological roles to genes and other genomic elements on a genome-wide scale, while comparative genomics infers function and evolutionary history by aligning and contrasting the genomes of different species.

Scope

This topic covers the annotation of genomes to identify genes and regulatory elements, the high-throughput study of expression through transcriptomics, the systematic assignment of gene function through knockouts and screens, the alignment and comparison of genomes across species to detect conserved and divergent regions, the inference of orthologs and paralogs, and the genome browsers and databases that organize this information. It treats the interpretation of genome sequence; the determination of that sequence is covered in the adjacent topic.

Core questions

• How are genes and regulatory elements identified and annotated in a raw genome sequence?
• How does measuring expression across conditions reveal what genes do?
• How does sequence conservation across species point to functional importance?
• How are orthologs and paralogs distinguished, and why does it matter?

Key concepts

• Genome annotation of genes and regulatory elements
• Transcriptomics and expression profiling
• Functional screens and gene knockouts
• Cross-species sequence alignment and conservation
• Orthologs, paralogs, and genome browsers

Mechanisms

Annotation combines sequence signals such as open reading frames and splice sites with evidence from expressed transcripts; comparative analysis aligns genomes so that sequences conserved beyond what neutral evolution would allow stand out as likely functional, while gene duplications and losses trace lineage-specific innovation.

Clinical relevance

Functional and comparative genomics prioritize candidate disease genes, interpret the likely impact of variants by their conservation, guide the choice of model organisms, and supply the annotations and browsers clinicians and researchers use to make sense of patient genomes.

History

As genome sequences accumulated from the late 1990s, the focus shifted from sequencing to interpretation: large consortia annotated functional elements, model-organism comparisons revealed deep conservation, and public genome browsers such as the UCSC browser launched in 2002 made genome-wide annotation broadly accessible.

Key figures

• David Haussler
• Eric Lander
• Michael Ashburner

Seminal works

• kent2002
• brown2018

Frequently asked questions

What is the difference between functional and comparative genomics?

Functional genomics asks what genomic elements do, often through experiments measuring expression or the effect of disrupting genes, while comparative genomics infers function and evolutionary history by comparing the genomes of different species.

Why does sequence conservation suggest function?

Regions that perform an important function tend to be preserved by natural selection across long evolutionary time, so sequences that remain similar across distantly related species are likely to be functionally constrained rather than free to mutate.