Related Experiment Videos
The sexual nature of the eukaryote genome
1Biology Department, McGill University, Montreal, Quebec, Canada.
Abstract:
This paper supports a previous conjecture that the sexual cycle of eukaryotes arose from the infection of cells by genome parasites. The finding are as follows. (1) In prokaryotes, conjugative plasmids ensure their own spread by directing partial cell fusion. (2) Conjugative plasmids permit gene transfer between prokaryotes and eukaryotes, and can be integrated into the eukaryote genome. (3) Genes can be transferred between unrelated eukaryotes, and between different genomes within eukaryotic cells. (4) Elements such as transposons and retroviruses evolve as parasites of the eukaryote sexual system. (5) The mating-type genes of bipolar fungi are idiomorphic: alternative genes directing sexual specificity are dissimilar and non-homologous. It is argued that they arose as parasitic elements directing cell fusion, which have become integrated into the genome. (6) Mating-type idiomorphs in different taxa may be dissimilar, reflecting the independent acquisition of different infectious elements by different eukaryote lineages. (7) Sexual competence is rapidly lost through mutation accumulation or antagonistic pleiotropy during vegetative proliferation, so that many lineages are sexually sterile. (8) In multipolar systems, novel mating-type alleles arising by mutation spread in a parasite-like manner by virtue of their access to lineages which have become sexually sterile. (9) It is suggested that centromeres arise as devices to enable low copy number plasmids to persist. (10) Crossing over is favored if it enables the genes that direct it to unlink themselves from inferior genomes, or from the consequences of their own transposition.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
The sexual cycle in eukaryotes likely originated from genome parasites infecting cells. These parasites facilitated gene transfer and evolved into key components of eukaryotic reproduction and genome organization.
Area of Science:
- Evolutionary Biology
- Genetics
- Molecular Biology
Background:
- Conjugative plasmids in prokaryotes facilitate gene transfer via cell fusion.
- Gene transfer mechanisms exist between prokaryotes and eukaryotes, with plasmid integration into eukaryotic genomes.
- Eukaryotic genomes exhibit gene transfer between unrelated species and within cells.
Purpose of the Study:
- To support the conjecture that eukaryotic sexual cycles originated from genome parasite infections.
- To explore the parasitic origins of key eukaryotic reproductive and genomic elements.
Main Methods:
- Comparative analysis of gene transfer mechanisms in prokaryotes and eukaryotes.
- Examination of mobile genetic elements (transposons, retroviruses) and their relationship to eukaryotic sexual systems.
- Analysis of mating-type genes (idiomorphs) in fungi and their proposed parasitic origin.
Main Results:
- Conjugative plasmids enable gene transfer and integration into eukaryotic genomes.
- Transposons and retroviruses act as parasites of the eukaryotic sexual system.
- Mating-type idiomorphs in fungi are proposed to be integrated parasitic elements driving cell fusion, with variations reflecting independent acquisitions.
- Sexual competence loss is common, and novel mating-type alleles spread parasitically.
- Centromeres may have evolved for plasmid persistence, and crossing over favors gene unlinking from inferior genomes.
Conclusions:
- The eukaryotic sexual cycle likely arose from the integration of genome parasites.
- Parasitic elements have shaped key aspects of eukaryotic reproduction, including mating-type determination and genome organization.
- Mobile genetic elements and their interactions provide insights into the evolutionary origins of eukaryotic complexity.