The human genome is the complete set of nucleic acid sequence for humans, encoded as DNA within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. Human genomes include both protein-coding DNA genes and noncoding DNA, haploid human genomes, which are contained in germ cells consist of three billion DNA base pairs, while diploid genomes have twice the DNA content. The Human Genome Project produced the first complete sequences of human genomes, with the first draft sequence. The human genome was the first of all vertebrates to be completely sequenced, as of 2012, thousands of human genomes have been completely sequenced, and many more have been mapped at lower levels of resolution. The resulting data are used worldwide in biomedical science, anthropology, forensics, there is a widely held expectation that genomic studies will lead to advances in the diagnosis and treatment of diseases, and to new insights in many fields of biology, including human evolution. Although the sequence of the genome has been completely determined by DNA sequencing. There are an estimated 19, 000-20,000 human protein-coding genes, in June 2016, scientists formally announced HGP-Write, a plan to synthesize the human genome. The total length of the genome is over 3 billion base pairs. The genome is organized into 22 paired chromosomes, plus the X chromosome and, in males only and these are all large linear DNA molecules contained within the cell nucleus. The genome also includes the mitochondrial DNA, a small circular molecule present in each mitochondrion. Basic information about these molecules and their content, based on a reference genome that does not represent the sequence of any specific individual, are provided in the following table. Chromosome lengths were estimated by multiplying the number of base pairs by 0.34 nanometers, variations are unique DNA sequence differences that have been identified in the individual human genome sequences analyzed by Ensembl as of December,2016. The number of identified variations is expected to increase as further personal genomes are sequenced and analyzed, in addition to the gene content shown in this table, a large number of non-expressed functional sequences have been identified throughout the human genome. Links open windows to the reference chromosome sequences in the EBI genome browser, small non-coding RNAs are RNAs of as many as 200 bases that do not have protein-coding potential. These include, microRNAs, or miRNAs, small nuclear RNAs, or snRNAs, long non-coding RNAs are RNA molecules longer than 200 bases that do not have protein-coding potential. Although the human genome has been sequenced for all practical purposes. A recent study noted more than 160 euchromatic gaps of which 50 gaps were closed, however, there are still numerous gaps in the heterochromatic parts of the genome which is much harder to sequence due to numerous repeats and other intractable sequence features. The content of the genome is commonly divided into coding and noncoding DNA sequences
Graphical representation of the idealized human diploid karyotype, showing the organization of the genome into chromosomes. This drawing shows both the female (XX) and male (XY) versions of the 23rd chromosome pair. Chromosomes are shown aligned at their centromeres. The mitochondrial DNA is not shown.
TSC SNP distribution along the long arm of chromosome 22 (from http://snp.cshl.org/ ). Each column represents a 1 Mb interval; the approximate cytogenetic position is given on the x-axis. Clear peaks and troughs of SNP density can be seen, possibly reflecting different rates of mutation, recombination and selection.