![]() “These parts of the human genome that we haven’t been able to study for 20-plus years are important to our understanding of how the genome works, genetic diseases, and human diversity and evolution,” Miga said. The new sequence also reveals previously undetected segmental duplications, long stretches of DNA that are duplicated in the genome and are known to play important roles in evolution and disease. These include highly repetitive DNA sequences found in and around important chromosomal structures such as the telomeres at the ends of chromosomes and the centromeres that coordinate the separation of replicated chromosomes during cell division. ![]() ![]() The gaps now filled by the new sequence include the entire short arms of five human chromosomes and cover some of the most complex regions of the genome. It also corrects thousands of structural errors in the current reference sequence. The new reference genome, called T2T-CHM13, adds nearly 200 million base pairs of novel DNA sequences, including 99 genes likely to code for proteins and nearly 2,000 candidate genes that need further study. In 2019, Karen Miga, assistant professor of biomolecular engineering at UC Santa Cruz, and Adam Phillippy at the National Human Genome Research Institute (NHGRI) organized an international team of scientists-the Telomere-to-Telomere (T2T) Consortium-to fill in the missing pieces. ![]() Nevertheless, crucial regions accounting for some 8% of the human genome have remained hidden from scientists for over 20 years due to the limitations of DNA sequencing technologies. Since the first working draft of a human genome sequence was assembled at UC Santa Cruz in 2000, genomics research has led to enormous advances in our understanding of human biology and disease. The first truly complete sequence of a human genome, covering each chromosome from end to end with no gaps and unprecedented accuracy, is now accessible through the UCSC Genome Browser and is described in six papers published March 31 in Science. ![]()
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