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Evolution at the mouse t complex: why is the t haplotype preserved as an integral unit?
1Institute for Animal Science and Health, Lelystad, The Netherlands. m.vanboven@id.wag-ur.nl
Evolution; International Journal of Organic Evolution
|December 7, 2000
Summary
Segregation distorters, like those in mouse t haplotypes, can spread even without full integration. Surprisingly, simpler "insensitive" forms often outperform "complete" t haplotypes in simulations.
Area of Science:
- Population genetics
- Evolutionary biology
- Genetics
Background:
- Segregation distorters are selfish genetic elements that bias inheritance.
- The t complex in house mice involves distorter loci acting on a responder locus, forming a 't haplotype'.
- It was hypothesized that the integration of components into a 'complete' t haplotype is key to their evolutionary success.
Purpose of the Study:
- To investigate the evolutionary success of integrated versus non-integrated segregation distorter systems.
- To test the hypothesis that complete t haplotypes are crucial for the evolutionary success of segregation distorters.
Main Methods:
- Utilized a population genetical metapopulation model.
- Simulated scenarios with varying degrees of t haplotype integration, segregation distortion, fitness, and recombination rates.
- Analyzed the invasion and frequency of different t haplotype configurations, including complete, partial, and insensitive forms.
Main Results:
- An 'insensitive' t haplotype, retaining only the responder locus, frequently invaded and reached high frequencies despite a segregation disadvantage.
- Complete t haplotypes were sometimes outcompeted by partial t haplotypes with lower segregation ratios in specific population structures.
- T haplotypes with recessive lethals only prevailed when the product of local population size and migration rate (Nm) was near one.
Conclusions:
- The close integration of components into a complete t haplotype may not be essential for the evolutionary success of segregation distorters.
- Partial or insensitive t haplotypes can be evolutionarily successful, challenging previous assumptions.
- The prevalence of lethal t haplotypes depends on population structure and migration rates, posing an evolutionary puzzle given their absence in natural populations.