Genome Size

Abstract

This article is about genome size, the mass of DNA in the genome of a cell. Living organisms show extensive variation in genome size that shows only a very loose, if any, relationship to organismal complexity. So while bacteria have smaller genomes than animals or plants, for example, some plants and protozoa have larger genomes than mammals (including humans), and the largest genomes among animals are seen in lungfishes and salamanders. Much of the observed variation in genome size involves large amounts of so-called ‘junk DNA’, including different kinds of repetitive DNA with no known function. In most eukaryotes, such as protists, fungi, plants, and animals, the junk DNA constitutes the vast majority of DNA in the genome (over 99.9% in some cases). While evidence is accumulating that junk DNA may actually harbor some functional DNA sequences, the vast majority of it may constitute ‘selfish DNA’ that really has no particular function other than self-replication. Evidence is also accumulating that genome size has effects on cell size and function, which can have an impact on the whole organism, including morphogenesis during embryonic development and regeneration.