genetic elements conflict
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how do genetic elements end up in conflict
components of some genomes have different transmission patterns such as nuclear and cytoplasmic genes so conflict arises. selection on element to increase its own transmission at the expense of the organism or other components, resulting in increased transmission of the SGE and decreased transmission of the other GEs
most SGEs contrived to be transmitted to a disproportionate fraction of the organism's progeny, what are the 3 ways they can do this
- interference, kill offspring w/o SGE
- gonotaxis- move towards germline
cytoplasmic male sterility
conflict btw nuclear and cytoplasmic genes. cytoplasmic genes are transferred in the female gametes to offspring so males are a dead end. male sterility caused by mitochondrial genes. CG causes male sterility- then plant has more resources to put into female function, more seeds, pollinated- CG increases in frequency. nuclear genes suffer as sex ration skewed to female bias, males more valuable- total repro of plant is reduced. male sterility gene can be favoured if it only increases female function slightly. nuclear restorers- return pollen production. gynodioecy can result- some plants female function only, others both male and female
Kozielksa et al 2009
2 tightly linked loci- recognition locus and distorter locus- control process. recognition locus- recognition sequence + distorter allele protein binds to it, no effect if it is a distorter recognition sequence. if the distorter allele protein binds to any other sequence, it can prevent chromosome from entering sperm, leading to distortion in favour of chromosomes containing the SD gene. 90% of offspring from Drosophila have sd Gene. male heterozygotes- sperm containing other genes fail to develop- great selective adv. any allele that gets into more than half the heterozygote's offspring automatically increases in frequency and spreads through population
cameron and Moav 1957
Nicotiana tabacum- plants w nicotiana plumaginofolia chromosome present as supernumerary- pollen w/o supernumerary killed. transmitted to 95% of progeny. transmission via females= 15% due to loss at meiosis.
richard dawkins- selfish gene
a parent helps its young- genes in parent are helping propagate copies in offspring. helper and non-helper genes aren't in conflict as they both have 0.5 probability that they will be passed to offspring, agree on value of offspring
what types of genes increase in frequency
genes that build better organism= survival/ fertility/ fecundity/ attractiveness/ better helper. outcompetes other alleles at same locus.
some genes manipulate repro to directly favour their spread, dont necessarily make better organism. some genes (transponsons) spread along genome, making multiple copies of themselves.
repro manipulation necessarily involves conflict- by manipulating host's repro, ultraselfish gene will directly harm other genes e.g. at same locus around meiosis/ indirectly harm other genes by harming or affecting the organism or its offspring
b chromosomes- PSR (paternal sex ratio)
b chromosomes=nuclear DNA, not needed for normal function, have deleterious effect on organism carrying them, preferentially passed on at meiosis. dont compete w non-distortin allele. PSR found in Nasonia vitripennis. usually, unfertilised eggs- males, fertilised- females. host patches w one/ more mated female wasps colonising each patch, lay eggs. males cant fly, females mate, often w brothers, on emergence, then disperse to new hosts. paternally transmitted B chromosome causes all male broods. PSR facilitates paternal transmission by causing condensation of entire genome in sperm, perhaps by preventing nuclear chromosomes from unpacking. diploid fertilised egg converted into haploid egg=male. PSR converts egg into sex which transmits PSR. destroys any genes transmitted w sperm
alfa-proteobacterium. occurs 15-75% all insects. transmitted to next gen via eggs not sperm. manipulates host into producing female biased broods: selectively kills male offspring, feminises genetic males, induces parthenogenesis, cytoplasmic incompatibility.
why does species-level cost of wolbachia not prevent their evolution
even at high frequency a sex ratio distorter transmits more of its genes to future generations than a symbiont not distorting the ration
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