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What are the costs (if any) associated with carrying lots of genetic material (Big genome size)?

  • energy for copying?
  • raw material for copying?
  • space in the cell?
  • Maintenance cost (matter and energy)?
  • time to copy is a limiting factor for the minimum generation time?
  • Less robustness?
  • More likely to evolve a gene that spreads well but has a negative fitness impact on the rest of the genome (selfish gene or outlaw)?

The answer probably depends on the organism. I am interested about any information concerning uni- or multi-cellular eukaryotes, bacteria or viruses.

Do we have any knowledge about how important are these costs or is it pure guesses?

This post comes in reaction to @AlanBoyd comments on this post.

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  • $\begingroup$ It may also have negative effects due to mutations in genes which are not really needed but develop a negative effect. $\endgroup$
    – Chris ♦
    Commented Apr 14, 2014 at 20:41
  • $\begingroup$ What would be the cost of cleaning up this material? $\endgroup$
    – oɔɯǝɹ
    Commented Apr 18, 2014 at 21:02
  • $\begingroup$ What do you mean "cleaning up this material"? $\endgroup$
    – Remi.b
    Commented Apr 19, 2014 at 16:18
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    $\begingroup$ Related question: biology.stackexchange.com/questions/10442/… $\endgroup$
    – Oreotrephes
    Commented Apr 22, 2014 at 15:16

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It is generally known that the smaller (or less complex) an organism is, the more "condensed" it's genome is. For example, bacteria (or some eukaryotes) have operons (http://en.wikipedia.org/wiki/Operon) or overlapping genes using different and they don't have introns, which alltogether saves a lot of space.

There are many reasons for that. Available space in the cell is definitely not one if it, however. Energy for copying and maintenance is a good point, but you have to keep in mind how evolution works. Bacteria and unicellular eukaryotes are usually adapted to a very specific environment in which they can reproduce rapidly. This means, they only need a small set of genes, specific for this environment and they have to reproduce very frequent, which means they are very prone to mistakes during DNA-copying. Such a mistake can lead to the death of the cell, which in this case equals the death of the organism.

In higher organisms however, the advantages of a bigger genome outweigh the disadvantages by far. Evolution can happen much faster because and mistake while copying does not necessarily lead to the death of the whole organism. Adaptation to a much greater variety of conditions is also necessary, e.g. when you look at plants: Their genomes are (on avarage) much bigger than the ones we mammals have, because they cannot move if the conditions around them become unpleasent. Instead, they need to find a way to adapt. This means, a big genome is in this case a fitness bonus. More interestingly, plant genoms are highly mutable (http://en.wikipedia.org/wiki/Transposable_element), which was originally thought to be a huge disadvantage.

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  • $\begingroup$ Plants also often carry a lot more copies of their chromosomes than animals, I've heard of plants with 8 copies of each chromosome, creates a lot of opportunity to carry multiple alleles for a gene and use whatever works best for the current situation. $\endgroup$
    – user137
    Commented Aug 20, 2014 at 23:48
  • $\begingroup$ This answer makes very little sense. First, organism size and complexity are not always that related, (i.e. bull kelp and a shrew). Second, it is false that organismal complexity relates to genome size. This is true for prokaryotes, but less for viruses, and entirely untrue for eukaryotes. In fact, Polychaos dubium is a single-cell amoeba that has a genome ten times larger than humans. Or, for instance, the fact that amphibians lead the animal kingdom in genome sizes. Third, genome size does not correlate with vagility, for instance, worms and fungi have much large genomes than birds. $\endgroup$
    – et is
    Commented Nov 26, 2016 at 20:45
  • $\begingroup$ You clearly have not read my answer very carefully. I never claimed that organismal complexity relates to genome size. In fact, I argued that plants have bigger genomes than mammals, even though you will hopefully agree with me that mammals are much more complex organism. Furthermore, we are talking about generals trends and avarages here. Of course you can find plenty of exceptions - and Polychaos dubium clearly is one of them. $\endgroup$
    – bgbrink
    Commented Dec 6, 2016 at 13:39

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