Longevity Briefs: Filling The Gaps In The Human Genome

Posted on 17 June 2021

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: Two decades ago, the Human Genome Project made the momentous announcement that the human genome had been sequenced. Except it hadn’t – at least, not fully. Due to the sequencing technology that existed at the time, it was impossible to work out how certain sections of the genetic code fit together, especially those with many repeating base pairs (the genetic letters G, A, C and T). Some of these sections have since been pinned down, but the most recent human genome is still missing around 8% of the full sequence. This missing 8% isn’t ‘junk’ either – there are hints that some of this unsequenced code may be involved in diseases like cancer.

What did the researchers do: Researchers in the Telomere-to-Telomere (T2T) Consortium have reported in a preprint paper that they have sequenced the remainder of the human genome. Instead of taking a DNA sample from a living person, they used cells derived from a complete hydatidiform mole – a type of tissue that forms when a sperm fertilises an egg with no nucleus. These cells contain chromosomes only from the male, meaning that researchers don’t need to distinguish between the genomes of two individuals. They also used new laser-based sequencing technology that allows larger sections of DNA to be read at a time. This is important because larger sections of DNA are more likely to contain unique sequences that overlap with other sections, making it easier to work out where that section belongs within the genome.

Completing the human genome: Chart showing number of base pairs sequenced since the year 200 up to a total of 3056,899,953.
The number of sequenced base pairs in the human genome over time.

Key takeaway(s) from this research: The newly sequenced regions number nearly 200 million base pairs and include 115 new genes which are predicted to code for proteins, bringing the total to 19,969. While there are no more gaps, some regions were harder to sequence than others, and researchers estimate that about 0.3% of the genome might still contain errors. Furthermore, the sperm cell that formed the hydatidiform mole carried an X chromosome, meaning that the Y chromosome has not yet been fully sequenced.

Work to sequence the Y chromosome with the same method is underway, and there are also plans to sequence 300 genomes from people all over the world. This will help us to understand which parts of the newly sequenced regions differ between individuals.

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The complete sequence of a human genome: https://doi.org/10.1101/2021.05.26.445798

A complete human genome sequence is close: how scientists filled in the gaps: https://www.nature.com/articles/d41586-021-01506-w

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