Genome size - a species comparison
This infographic compares the sizes of different genomes for a selection of species, from fish and plants to mammals and even bacteria.
Genomes vary wildly in size
Genome sizes exhibit a remarkable diversity across different species, with measurements in base pairs (bp) that form the DNA’s double helix structure (see the image at the end of the article). The infographic illustrates this by comparing the smallest and largest known genomes per kingdom, showcasing the amazing range. Plants have one of the widest ranges while bird genomes seem to stick to a tighter script.
The human genome has around 3.2 billion base pairs. This is a lot of DNA but not the biggest genome. The largest genome sequenced so far is that of a lily Paris japonica (Melanthiaceae)! There are even types of cicada and grasshopper with larger genomes than a person. Unsurprisingly, bacteria and viruses have the smallest genomes. However, size isn't everything. An organism’s complexity doesn't necessarily scale with genome size.
Some genes code for proteins, some don’t
For most genomes, only a fraction of the DNA sequence consists of coding genes. These are genes which build proteins and trigger actions in cells. In humans, just 1/30th of the 3.2 billion base pairs are coding genes. The rest is sometimes referred to as “junk DNA”, but some scientists say this term for the repeats and duplications in a genome sequence is misleading.
Genome size, growth rate, ecology, and evolution
Genome size can affect how fast organisms grow and may be influenced by ecology. More DNA means cells take longer to copy and divide, which can slow down development. This is seen in plants with larger genomes that tend to grow more slowly. They may be less able to adapt to changes in the environment. Smaller genomes on the other hand can lead to faster growth, as seen in some desert plants that spring up after it rains.
From an evolutionary perspective, having less DNA can lead to a faster metabolism, which frees up energy for more demanding processes, like flight. The efficient flight and fast metabolism seen in birds may stem from their dinosaur ancestors shedding genetic material. It's a trade-off, evolution in action.
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Here’s Why Great White Sharks are Natural-Born Superheroes, 19 Feb 2019, https://www.livescience.com/64799-great-white-shark-genome.html
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