By Melissa Fryman  

Since the Human Genome Project published almost two decades ago, the field of genomics has exploded, raising questions we didn’t even know to ask at the start of this millennium.

A little-known fact—outside of the biomedical research community—is that the original reference human genome was incomplete. Roughly 8% of it was unknown, and until just last year, there were still around 100 gaps in the sequence.

Many of the gaps were located at specialized points of attachment between chromosomes, called centromeres. Additional gaps were located at the short ends of acrocentric chromosomes, where one of the chromosomes arms is substantially shorter than the other, of which humans normally have five pairs. Replete with repetitive DNA elements, these gaps were notoriously difficult to assemble with standard methods.

Proper centromere function is essential for faithful cell division and chromosome segregation; problems with centromere function can lead to cancer, or chromosomal disorders such as Down syndrome and Fragile X syndrome.

In acrocentric chromosomes, the centromere is located near the end, or telomere, of the chromosome. The short arms of acrocentric chromosomes house ribosomal DNA, an array of nearly identical genes that support protein-producing ribosomes, in addition to other DNA sequences that are just now starting to be elucidated.

Assembling the complete human genome was an international, multi-institutional feat of creativity and technology by the Telomere-to-Telomere (T2T) consortium, which is headed by Karen Miga, PhD, from the University of California, Santa Cruz, and Adam Phillippy, PhD, from the National Human Genome Research Institute of the National Institutes of Health. Also part of the consortium are several Stowers researchers including Investigator Jennifer Gerton, PhD.