I understand that new genomes are being sequenced ever day and these answers replace themselves often; although as of today, what has been proven to be the most genetically complex organism (Other than a human of course)? I keep getting a multitude of different answers like Daphnia pulex, Axolotl, Paris japonica or Adder’s Tongue all from different dates and sources so it becomes difficult to tell what is the right answer here if any. If this question is not specific enough I would be happy to revise.

Edit: I would define genetic complexity as either genome size or number of genes. Either answer would work. If you would like give other information like chromosomes or isoforms from any other definition, that would be helpful. Whatever is the best of the best.

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    $\begingroup$ I think one of the biggest problem with this (type of) question is how you define 'genetically complex' - there a lot of different things one can consider (and weigh differently): genome size, number of genes, genome architecture, isoforms and/or copies per gene, (alternative) splicing, regulatory interactions of genes (at different levels). Additionally its worth to note that we know a lot more about the human (or also mouse genome) than most others - just because we haven't found things like cryptic transcripts or circular RNA's in other species (yet), doesn't mean they don't exist. $\endgroup$
    – Nicolai
    Commented Jan 22, 2019 at 12:18
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    $\begingroup$ Complexity is not the length of a genome, but the amount of information encoded in it. (See Information Theory.) And even that isn't the whole story, since some "simplifications" like mammalian live birth & post-natal care can lead to a more complex result... $\endgroup$
    – jamesqf
    Commented Jan 22, 2019 at 18:03

1 Answer 1


Edit: I would define genetic complexity as either genome size or number of genes. Either answer or information would work.

Largest genome: Paris japonica, a rare plant. Its genome is 149,000,000,000 base pairs large. Approximately 50 times larger than the human genome, by base pair count.

Higher number of genes in an organism: Daphnia pulex, a very common species of water flea. 31,000 protein-coding genes.

As already pointed out, the most genetically complex organism is an unclear question. Complexity can be interpreted in different ways, and I don't think we could agree on a satisfying measure (or definition, for that matter) of genetic complexity.


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