A team of scientists has completely sequenced the human X chromosome. This is the first time that a human chromosome has been fully sequenced.
Science is getting closer and closer to knowing the totality of the human genome and has recently taken another major step in that direction. A team of researchers sequenced the entire X chromosome, covering more than three million base pairs that had never been mapped before.
“These repeat-rich sequences were once deemed intractable, but now we’ve made leaps and bounds in sequencing technology. With nanopore sequencing, we get ultra-long reads of hundreds of thousands of base pairs that can span an entire repeat region, so that bypasses some of the challenges,” explained the article’s lead author, Karen Miga, from the University of California, Santa Cruz.
“We’re starting to find that some of these regions where there were gaps in the reference sequence are actually among the richest for variation in human populations, so we’ve been missing a lot of information that could be important to understanding human biology and disease,” she added
In humans, the X chromosome is one of the sex-determining chromosomes. Generally, a zygote that receives two X chromosomes is biologically female, while an X and Y chromosome results in a male.
The team of researchers did not sequence an X chromosome from a normal human cell. The team studied a special type of cell that contains two identical chromosomes, part of a model genome called CHM13.
To successfully sequence the entire chromosome, scientists used a new technique called nanopore sequencing. With this technique, the researchers were able to fill a huge gap that comprised about 3.1 million base pairs of repetitive DNA.
The results of the study were published Tuesday in the scientific journal Nature. There are still 23 other chromosomes left in the Human Genome Project, which started in 1990 and plans to map all of them by the end of 2020.