What's in a genome? The C-value enigma and the evolution of eukaryotic genome content

Abstract

One contribution of 17 to a theme issue 'Eukaryotic origins: progress and challenges'. What's in a genome? The C-value enigma and the evolution of eukaryotic genome content Tyler A. Elliott and T. Ryan Gregory Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1 Some notable exceptions aside, eukaryotic genomes are distinguished from those of Bacteria and Archaea in a number of ways, including chromosome structure and number, repetitive DNA content, and the presence of introns in protein-coding regions. One of the most notable differences between eukaryotic and prokaryotic genomes is in size. Unlike their prokaryotic counterparts, eukaryotes exhibit enormous (more than 60 000-fold) variability in genome size which is not explained by differences in gene number. Genome size is known to correlate with cell size and division rate, and by extension with numerous organism-level traits such as metabolism, developmental rate or body size. Less well described are the relationships between genome size and other properties of the genome, such as gene content, transposable element content, base pair composition and related features. The rapid expansion of 'complete' genome sequencing projects has, for the first time, made it possible to examine these relationships across a wide range of eukaryotes in order to shed new light on the causes and correlates of genome size diversity. This study presents the results of phylogenetically informed comparisons of genome data for more than 500 species of eukaryotes. Several relationships are described between genome size and other genomic parameters, and some recommendations are presented for how these insights can be extended even more broadly in the future.

Nuclear DNA content correlates with depth, body size, and diversification rate in amphipod crustaceans from ancient Lake Baikal, Russia

“…This difference may simply be due to experimental error and slight differences in the fluorescence Salemaa and Kamaltynov (1994) found little variation in chromosome number (n=26 or n=32 chromosomes for 13% and 39% of the described Baikal species and genera respectively, including 12 of the genera in the present study), suggesting that differences in genome size may be the result of some other process. This is likely to be the proliferation of repetitive DNA such as transposable elements, which are more abundant in larger genomes (Elliott et al 2015a(Elliott et al , 2015b. Investigation of the other 87% of described species for which chromosome data does not exist will provide further evidence to either support or reject polyploidy as a mechanism which explains the differences in genome size observed here.…”

Changing ideas about eukaryotic origins

“…These differences may arise from the fundamental changes in the population genetic environment that accompanied the origin of eukaryotes, ranging from increased cell size (and concomitant reduction in population densities) to the evolution of meiosis and sex. The relative contributions of genetic drift [54], mutation [55] and selection [56,57]-perhaps at multiple levels [58]-to the origin and evolution of eukaryotes and their genomes remains a fascinating area of debate, and broad comparative data of the type presented by Elliott & Gregory [53] will continue to play an important role in contrasting the predictions of the leading hypotheses.…”

Dynamics of genome size evolution in birds and mammals

“…genome size evolution | DNA loss | transposable elements | amniotes | flight T he nature and relative importance of the molecular mechanisms and evolutionary forces underlying genome size variation has been the subject of intense research and debate (1)(2)(3)(4)(5)(6)(7). Variation in genome sizes may not always occur at a level where natural selection is strong enough to prevent genetic drift to determine their fate (neutral or effectively neutral variation) (3).…”