What living things have the largest or most complex genome?

Krishna: You said living beings. Okay.

Among all living beings, Scientists have discovered that Paris japonica, a striking rare native of Japan, has the largest genome of them all -- bigger than the human genome and even larger than the previous record holder -- the marbled lungfish (2,3,5).

Paris japonica

Image source: google images

Paris japonica, the Japanese canopy plant, has the largest genome of any organism analysed to date. At 149,000 million base pairs (mega bp or Mbp) of DNA, it’s about 50 times bigger than the human genome. At the other end of the scale, the flowering plant with the smallest genome is Genlisea tuberosa, a tiny carnivorous plant found in Brazil, coming in at 61 Mbp (4).

There is a staggering diversity of genome sizes. The smallest genome (3) so far reported (0.0023 pg of DNA) is found in a parasite (Encephalitozoon intestinalis) of humans and other mammals. The human genome, at 3.0 pg, is 1300 times larger than this, but this pales into insignificance compared to those found in some animals and plants.

Among animals, some amphibians have enormous genomes, but the largest recorded so far is that of the marbled lung fish.

The marbled lungfish has the largest recorded genome of any eukaryote. One haploid copy of this fish's genome is composed of a whopping 132.8 billion base pairs, while one copy of a human haploid genome has only 3.5 billion (1).

The marbled lungfish has a very long genome

Image source: New Scientist

Genome size is usually measured in picograms [pg] and then converted to nucleotide number. One pg is equivalent to approximately 1 billion base pairs. Therefore, genome size is clearly not an indicator of the genomic or biological complexity of an organism. Otherwise, humans would have at least as much DNA as the marbled lungfish, although probably much more.

As further clarification, when scientists talk about the eukaryotic genome, they are usually referring to the haploid genome—this is the complete set of DNA in a single haploid nucleus, such as in a sperm or egg. So, saying that the human genome is approximately 3 billion base pairs (bp) long is the same as saying that each set of chromosomes is 3 billion bp long. In fact, each of our diploid cells contains twice that amount of base pairs. Moreover, scientists are usually referring only to the DNA in a cell's nucleus, unless they state otherwise. All eukaryotic cells, however, also have mitochondrial genomes, and many additionally contain chloroplast genomes. In humans, the mitochondrial genome has only about 16,500 nucleotide base pairs, a mere fraction of the length of the 3 billion bp nuclear genome .

But as scientists discover more and more about our natural world, these things keep changing from time to time. Keep that in mind. We have to update ourselves very frequently.

Footnotes:

1. Eukaryotic Genome Complexity
2. Rare Japanese plant has largest genome known to science
3. http://Jaume Pellicer, Michael F. Fay, Ilia J. Leitch. The largest eukaryotic genome of them all? Botanical Journal of the Linnean Society, 2010; 164 (1): 10 DOI: 10.1111/j.1095-8339.2010.01072.x
4. https://www.darwintreeoflife.org/news_item/genomes-great-and-small-...
5. https://academic.oup.com/botlinnean/article/164/1/10/2418538?login=...