Genes with new functions originate in a eukaryotic genome at a small scale, mainly through mutations, interactions with transposable elements and horizontal transfer of genes from cytoplasmic genomes. On a large scale, genes originate through events of genome duplications; this is studied widely. Functions are not only gained; they are also lost. However, through major events in the evolution of an organism, the function of a perfectly operating gene might
become redundant and therefore lost. The consequences of a loss of function for individual genes are documented; however, the genomic consequences of radical changes, like becoming dependent on another organism or losing an entire life stage. This project aims to address this question using four model eukaryotic genomes. The human follicle mites, Demodex spp., are the only higher organisms that are parasitic but no longer infectious. This heritage should lead
to extreme genome reduction through loss of function. For the first time, Demodex genome of this model organism will be sequenced using the new technique of single molecule real time (SMRT) sequencing to obtain larger portions of the entire genome than are currently possible with commonly used next-generation sequencing methods. By using the Kyoto Encyclopedia
of genes and Genomes (KEGG) metabolic pathways we found gene losses for various parts of metabolism with respect to the involved pathways under the comparison between Demodex vs Metaseiulus and Tetranychus also Acari and Drosophila melanogaster. As well as in Acariformes against Parasitiformes, Dermatophagoides farina, Past-Host-Associated organism has been found to return to its free-living lifestyle as a free-living organism. The comparisons of the Past-Host-Associated activities with the Associated-Host has been found
to have a gene gain in respect to different metabolic pathways.