Circles of Life
Genomes across time
I am the daughter of the earth and water,
And the nursling of the sky;
I pass through the pores of the ocean and shores;
I change, but I cannot die.
— Percy Bysshe Shelley (The Cloud)
Time brings change — and genomic mutations. We can see this when we compare genomes of different species — the older their common ancestor, the greater the accumulated differences, and the lower the overall similarity in their genomes.
The Circles of Life — Genomes across time poster shows this idea at a glance by visualizing comparisons between the human (Homo sapiens) genome and the genome of five other species: chimp (Pan troglodytes), dog (Canis familiaris), opossum (Monodelphis domestica), platypus (Ornithorhynchus anatinus), and chicken (Gallus gallus).
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contents
- 1 · Circles of life
- 2 · Exhibit at British Library
- 3 · Circles of Life — Genomes across time: the poster
- 4 · Circles of Life — Genomes across time: Species by species
Visualizing differences (or similarities) between genomes is difficult — the genomes themselves are large (billions of bases) and their differences are numerous (millions) and varied in size (from 1 to 1000's of bases).
One way to approach drawing compact representations of differences is to use my Circos software, which was designed for this task.
The circles on the poster are grouped into 5 pairwise comparisons. Within each group (e.g., chimp), there are 24 circles. Each circle compares a human chromosome (1, 2, 3, ...) to the entire genome of another organism (e.g., chimp). Within the circle the ribbons indicate regions of high sequence similarity.
As time passes — here, meaning the further back in time the pair shared a common ancestor — the sequence similarities fade.
It takes a few minutes to get used to this way of depicting data — the interpretive panel (see below) guides you through the visualization.
This art was originally shown at the British Library's “Beautiful Science: Picturing Data, Inspiring Insight” exhibit in 2014.
The art also appeared on the invitation.
The full-size panels shown here have been modified slightly from the originals shown at the British Library — but the data are the same.
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All organisms on Earth are descended from a common ancestor, believed to have lived some 3.5 billion years ago.
As time passes, physical or environmental isolation causes populations to accumulate genetic differences that eventually prevent them from reproducing with one another. This is how new species arise.
The tree of life depicts how all living organisms are related through evolution. The tree is reconstructed by comparing the genomes of different species to identify shared and unique DNA sequences. Species that share a more recent common ancestor, such as humans and chimpanzees, have more similar genomes than species that are more distantly related.
Genome similarity is often visualized using Circos diagrams, in which chromosomes are arranged in a circle. Links between chromosomes or genomic regions represent areas of sequence similarity.
Each circle of life depicts the sequence similarity between a single human chromosome (scaled to bottom half of the circle) and the entire genome of another species (scaled to top half of the circle).
The genome of an organism represents its hereditary information.
It is encoded by millions of base pairs chained together in a very large molecule called DNA. Tightly wound DNA is packaged into chromosomes that are found in a cell’s nucleus.
Regions in the genome called genes act as templates for the production of proteins that drive biochemical reactions.
By sequencing the genomes of different organisms and comparing the structure of genes and proteins, scientists can gain insight into evolutionary relationships.
Human (Homo sapiens, 23 chromosome pairs, 3.1 Gb) vs. chimp (Pan troglodytes, 24 chromosome pairs, 3 Gb).
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Human (Homo sapiens, 23 chromosome pairs, 3.1 Gb) vs. dog (Canis familiaris, 39 chromosome pairs, 2.4 Gb).
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Human (Homo sapiens, 23 chromosome pairs, 3.1 Gb) vs. opossum (Monodelphis domestica, 9 chromosome pairs, 3.6 Gb).
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Human (Homo sapiens, 23 chromosome pairs, 3.1 Gb) vs. platypus (Ornithorhynchus anatinus, 26 chromosome pairs, 1.9 Gb).
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Human (Homo sapiens, 23 chromosome pairs, 3.1 Gb) vs. chicken (Gallus gallus, 33 chromosome pairs, 1.1 Gb).
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