Genomics is the study of an organism's entire genome. The field includes intensive
efforts to determine the entire DNA sequence of organisms and fine-scale
genetic mapping efforts. The field also includes studies of intragenomic
phenomena such as heterosis, epistasis, pleiotropy and other interactions between
loci and alleles within the genome. In contrast, the investigation of single
genes, their functions and roles, something very common in today's medical and
biological research, and a primary focus of molecular biology, does not fall
into the definition of genomics, unless the aim of this genetic, pathway, and
functional information analysis is to elucidate its effect on, place in, and
response to the entire genome's networks
The transcriptome is the set of all messenger RNA (mRNA) molecules,
or "transcripts", produced in one or a population of cells. The term
can be applied to the
total set of transcripts in a given organism, or to the specific subset of
transcripts present in a particular cell type. Unlike the genome, which is
roughly fixed for a given cell line (excluding mutations), the transcriptome
can vary with external environmental conditions. Because it includes all mRNA
transcripts in the cell, the transcriptome reflects the genes that are being
actively expressed at any given time, with the exception of mRNA degradation
phenomena such as transcriptional attenuation. The study of transcriptomics
examines the expression level of mRNAs in a given cell population, often using
high-throughput techniques based on DNA
microarray technology.