Lecture 7: intragenomic conflict Flashcards
groups of cooperators are known well at different levels:
- Genes in a genome (i.e. chromosome of Drosophila melanogaster)
- cells in a multicellular organism
- bees in a hive (honey bee queen and workers)
Conflict: Tennyson
- Tennyson 1850 ‘Nature, red in tooth and claw’
- -Animals competing over food
- male vs male conflicts
- plants competing for light or water
Richard dawkins
1976 ‘the selfish gene’
‘selfish gene’ what does this mean
- when one organism helps another (parent & offspring) the organism could be described as being altruistic (donor help recipient at a cost)
- but this behaviour to the gene is considered to be selfish (helping copy of their own genes in offspring)
- -level at organism = altruistic
- -level at gene = selfish
an organism whose altruistic behaviour is caused by
selfish genes
genes that help other genes at the detriment to themselves what would happen
they would be selected against & eliminated from gene pool
Are selfish genes in conflict?
parental genes at different autosomal loci typically have same probability to be passed on to offspring
-so no conflict among genes at different loci concerning how much to help the offspring
strategies for genes to follow to increase frequency in next generations:
1) build a better organism thereby enhancing total reproduction of bearer
2) manipulate host organisms reproduction to have a greater chance of being passed on to offspring (ultraselfish genes)
transposons
spread along genome making copies of themselves
ultraselfish genes:
- can be selected for even when they don’t help organism
- they can in fact harm the organism so that its total reproduction is diminished
ultraselfish gene at work: cytoplasmic male sterility
- maize plant is male sterile, no pollen on male tassel
- introgenomic conflict occurs between nuclear and cytoplasmic genes
- –> HHHHH
offspring has nuclear genes from ____, mitochondrial from __
mother and father,
mother only
–so males pass on no cytoplasmic genes
cytoplasmic male sterility: in many angiosperms
don’t produce pollen, so invest more in producing eggs
- functions as female only
- pollen from other plants then fertilise eggs to produce offspring
- -so if you were a mitochondrial gene you’d rather be in CMS
how could CMS evolve?
only has to produce a little extra female function in order to evolve
-as M are a dead end for mitochondrial genes in angiosperms
nuclear “restorer” genes
restore male functions in CMS
-conflict between cytoplasmic and nuclear genes –> with nuclear genes counteracting male sterility caused by cytoplasmic genes
conflict between nuclear genes at same loci: conflict occurs due to
meiosis
Females & meiosis conflict
meiosis results in egg & 3 polar bodies
-incentive for a gene to manipulate meiosis in females to increase its chance of being in egg rather than polar body
males & meiosis conflict
meiosis produces 4 or more sperm, so each allele ends up in a gamete
- conflict due to sperm competition
- incentive for allele to harm any sperm not containing that allele so it has fewer competitors
meiotic drive / segregation distortion =
unequal transmission of alternative alleles to offspring
segregation gene in drosophila
Segregation distorter (SD) - SD prevents the rival sperm from being made
segregation distorter gene in mouse
- t-locus (t gene)
- makes rival wild type sperm less competitive by deactivating them in the female reproduction tract
- knocks out wild type sperm after insemination once in female reproductive tract
segregation distorters on sex chromosome distorts
sex ratio
sex ratio distortion: an x-linked distorter cases a ____ biased sex ratio in the offspring of the male bearing it
female
meiotic drivers (or segregation distorters ) are more easily detected if they affect
the sex ratio
effect of mating system on distortion: monogamy
potential advantage from distortion can be great
effect of mating system on distortion: polyandry
advantage from distortion decreases as more sperm from multiple males to compete with distortion
effect of mating system on distortion: female mated to one male, male does not carry distorter gene
all sperm viable
effect of mating system on distortion: female mated w one male that carries distorter gene
sperm not carrying distorter gene are knocked out. Distorter sperm fertilise 100% of the eggs, not 50%
female mated to two males. 1 male carries distorter gene
- wild type sperm from distorter carrying male are knocked out
- other males sperm are unaffected
- distorter fertilises 33%
- -> reduces further with each mating
- female can poss dump distorter sperm so non-carrying male will be most successful –> cryptic female choice
Female _____ distorter sperm so distorter male fertilises 0 eggs
recognises and dumps
