• Question: Does it take longer to sequence a bigger animal?

    Asked by topquestionsfromchat to Barn Owl, Brown garden snail, Common Crane, Emperor Dragonfly, Hazel Dormouse, Catshark, Scotch Thistle, St Kilda Wren on 22 Nov 2017.
    • Photo: St Kilda Wren

      St Kilda Wren answered on 22 Nov 2017:

      Not necessarily. The length of time it takes to process a genome depends on how big it is, and how different it is from a comparator. For example, Common Crane’s genome is larger than mine, so you’d expect it to take longer to process. However, scientists might find that Crane’s genome is very similar to that of a related species, speeding up the process, while mine might be different or pose different problems and so take longer. So you see, it’s not the size of the animal that matters, but the size (and complexity) of the genome.

    • Photo: Lesser-Spotted Catshark

      Lesser-Spotted Catshark answered on 22 Nov 2017:

      You are quite right that it would take longer to sequence a longer genome…but…a larger animal does not necessarily have a larger genome! One of the strangest phenomenon in genomics is the ‘c-value paradox’. The c-value is a rough approximation of the size of an animal’s genome, sometimes expressed in weight (picograms) of DNA but more frequently now in mega-base pairs (Mb) or giga-base pairs (Gb). It was once thought that larger or more complex animals would have larger genomes. However it is now clear that there is absolutely no correlation between the size or complexity of an animal and the size of its genome! One of the largest genomes known is that of the lungfish which has a genome size of 120 Gb, which is about 40 times larger than a human genome! The smallest known is a pufferfish which is about 0.35 Gb, 10 times smaller than a human genome! An elephant has a genome size about the same as a human (3.2 Gb). There is a lot of debate amongst scientists exactly why this is the case but it seems the most likely answer is that a lot of DNA in a genome is simply ‘junk’ – unnecessary clutter accumulated over evolution which has neither a positive or negative effect on survival. But some people disagree!

    • Photo: Common Crane

      Common Crane answered on 27 Nov 2017:

      Like it is with many things in life, it varies from case to case. On top of the factors mentioned by St Kilda Wren and Lesser-Spotted Catshark I would add such a simple thing as resources – computational hardware, software and humans of course.

    • Photo: Emperor Dragonfly

      Emperor Dragonfly answered on 4 Dec 2017:

      Not really – there is a well known thought experiment called the onion test – “if you think that all the DNA in a genome is functional consider why an onion needs a genome 5 TIMES BIGGER that yours!”
      So, genomes can vary in size and it is clearly not related to the size of the organism – some singled celled amoeba’s have genomes a 200 times bigger than a humans. In most cases all this extra DNA does not seem to do very much, but perhaps we are just learning about it?

      The Emperor Dragonfly genome is half the size of a humans, so it might take a while to sequence, but we can now sequence a human genome in a matter of weeks so we won’t have to wait too long!

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