Salient Features of Human Genome Project

The completed Human Genome Project produced a long list of striking headline findings about the structure of the human genome. Although the human genome contains about 3 billion nucleotide base pairs in total, the DNA sequences that actually code for protein make up only about 5 percent of that total. The average human gene is built from around 3,000 bases, though gene size varies enormously; the single largest known human gene, dystrophin, spans about 2.4 million bases. Roughly half of the genome's functional significance is attributable to mobile, transposable genetic elements, particularly the LINE and ALU sequence families. The roughly 30,000-plus human genes are distributed unevenly across the 24 distinct human chromosomes (22 autosomes plus X and Y); chromosome 19 carries the highest density of genes of any human chromosome, while chromosome 13 and the Y chromosome both carry comparatively few genes for their size. The chromosomal arrangement of human genes shows considerable diversity from one chromosome to the next: chromosome 1 alone carries roughly 2,968 genes, whereas the Y chromosome carries only about 231. Current estimates place the total number of human genes somewhere between about 35,000 and 40,000, and, remarkably, roughly 99.9 percent of the nucleotide bases in the genome are identical across all people, meaning the genetic differences that distinguish one person from another involve only a very small fraction of the total sequence. The specific function of more than half of all the genes so far discovered still remains unknown, and coding sequences overall account for less than 2 percent of the entire genome; the great bulk of the genome instead consists of repeated sequences that do not directly code for anything, but which nonetheless provide valuable insight into chromosome structure, dynamics and evolutionary history, since patterns of genetic diversity are written into how these repeats vary. Scientists working on the project have also identified roughly 1.4 mi …