“Genetics” focuses on single genes and their effects, whereas “genomics” refers to the action of all of the genes in an organism. Genomics also refers to a set of associated technologies (eg, high-throughput sequencing, expression profiling with microarrays). Genomics, in both senses, was largely born of the Human Genome Project—the effort to sequence the human genome.
11 Facts to understand the human genome:
- The human genome contains 3,164 million chemical nucleotide bases, Adenine, Cytosine, Thymine, and Guanine (A, C, T, and G). The average gene consists of 3,000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases.
- The total number of genes is estimated at 30,000.
- Almost all (99.9%) nucleotide bases are exactly the same in all people.
- Repeated sequences that do not code for proteins (“junk DNA”) make up at least 50% of the human genome.
- Repetitive sequences are thought to have no direct functions. Over time, these repeats reshape the genome by rearranging it, creating entirely new genes, and modifying and reshuffling existing genes.
- The human genome’s gene-dense “urban centers” are predominantly composed of the DNA building blocks G and C.
- In contrast, the gene-poor “deserts” are rich in the DNA building blocks A and T. GC- and AT-rich regions usually are the light and dark bands we see on chromosomes. Genes appear to be concentrated in random areas along the genome, with vast expanses of non-coding DNA between.
- Stretches of up to 30,000 C and G bases repeating over and over often occur adjacent to gene-rich areas, forming a barrier between the genes and the “junk DNA.” These CpG islands are believed to help regulate gene activity.
- Chromosome 1 has the most genes (2,968), and the Y chromosome has the fewest (231).