Towards a better understanding of genome size evolution

11 Aug 2016. NUS scientists used flies to document rapid changes in the evolution of genome size in animals.

Genomes contain the genetic information necessary for the normal functioning, development and reproduction of all living species. Humans have 23 pairs of chromosomes with a genome size of approximately three billion DNA base pairs. This figure is 40 times smaller than the largest known animal genome of 130 billion base pairs which is present in the marbled lungfish. In animals, genome size can differ by more than 6,000-fold. Scientists are interested in understanding the evolution of genome size in living species because large genomes influence cell size, cell division rates and cell functions.

A research team led by Prof Rudolf MEIER and Lee Kuan Yew Postdoctoral fellow, Dr Kathy SU from the Department of Biological Sciences at NUS studied the evolution of genome size in a group of sepsid flies to investigate and understand the mechanisms involved and the rate of size changes. Their study found that the genome size in the flies is highly dynamic, with five genome expansions and four genome contractions identified. Between the largest and smallest genomes in the study, the variation in genome size could go up to a four-fold difference. They also discovered a recent genome size expansion of three times in a small group of Southeast Asian fly species, some of which can be found in Singapore. The changes to the genome size seem to be independent of the number of chromosomes as all the species in their study have six pairs of chromosomes.

Although next-generation sequencing techniques have revolutionised genomics, the selection of species for whole-genome sequencing has not changed much. Using a more genome-centric approach to select target species for whole genome sequencing by first understanding the innate genome properties in an evolutionary context could enhance understanding of genome evolution. Through this study, the research team has identified good candidates for in-depth genome sequencing projects to understand the mechanisms and consequences of rapid genome expansions.

Figure shows sepsids and their chromosomes. LEFT: Meropliosepsis sexsetosa, a bright yellow sepsid fly with the largest known genome size in this family. This species has six pairs of chromosomes with one pair that is particularly larger than the rest. RIGHT: Meroplius alberquerquei, sepsid with one of the smallest genome size. [Image credit: ANG Yuchen and Kathy Su]

Reference

Su KFY, Puniamoorthy J, Özsu N, Srivathsan A, Meier R. “Evolutionary analysis identifies multiple genome expansions and contractions in Sepsidae (Diptera) and suggests targets for future genomic research”. Cladistics. 32 (2015) 308-316.