Transcriptomic analysis of physiological systems

Sequencing of the genomes for numerous avian species has ushered in the era of functional genomics or transcriptomics for both wild and domestic species. Tools for genome-wide analysis of mRNA levels in individual samples have allowed investigators to address questions related to physiological systems that have remained open for decades. DNA microarrays were the first tool for transcriptional profiling of gene expression in avian species. However, this approach was rapidly replaced by high-throughput sequencing of cDNA libraries constructed from individual RNA samples or RNAseq. DNA microarrays and RNAseq have been used to identify genes and gene networks involved in numerous physiological processes ranging from vocalization in songbirds to body growth and composition in poultry. Transcriptomic studies provide lists of candidate genes involved in physiological processes, clusters of genes whose responses suggest regulation by common signals, and networks of genes that can be used to form a more holistic view of genetic regulation of physiological processes. With the sequencing of multiple avian genomes and the advent of RNAseq technology, genome-wide analysis of gene expression is now possible for both domesticated and wild avian species.