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Green Beard Genes
Context:
Scientists have gained valuable new insights into natural altruism by studying the amoeba Dictyostelium discoideum.
More on News:
- Studies suggest that altruistic worker bee genes can be passed on to the queen and offspring, even if the worker doesn’t reproduce.
- Green-beard genes enable individuals to recognise and cooperate, or potentially provoke harmful behaviour toward those carrying different versions of the gene.
Key Highlights:
- Altruism in Nature
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- Observed in human societies, animals, and microorganisms.
- Examples: worker bees, male widow spiders, and meerkats.
- Role of Green-Beard Genes
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- Green-beard genes allow individuals to recognise and cooperate with others carrying the same gene.
- Enhances chances of genetic material being passed on, even without reproduction.
- Two genes, tgrB1 and tgrC1, have been identified in Dictyostelium discoideum, displaying properties similar to green-beard genes.
- Mechanism of Action
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- The tgrB1 and tgrC1 genes encode cell surface proteins that facilitate self-recognition and cooperation among genetically similar cells.
- Strong binding between these proteins on the same strain triggers altruistic behaviour, leading to stalk formation.
- Weak binding due to genetic differences results in separation, not cooperation.
- Ensures altruistic sacrifice is directed towards genetically similar individuals.
- Polymorphism and Chimerism
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- Chimerism poses a risk of cheating: some strains avoid becoming stalk cells and dominate the spore population.
- Deletion of tgrB1 leads to cheating among kin, showing complex dynamics of cooperation and competition.
The Green-Beard Effect
What Are Green-Beard Genes?
- Green-beard genes are a fascinating genetic mechanism that allows individuals to recognise and preferentially cooperate with others who share the same gene variant.
- Gene that not only influences an individual’s behaviour but also carries a visible “tag” (like a green beard) that helps others recognise it.
How Do Green-Beard Genes Work?
- If a gene promotes altruistic behaviour in one individual (e.g., a worker bee), it also benefits the copies of that gene in related individuals (e.g., the queen and her offspring).
- These genes create a form of self-recognition, encouraging cooperation among carriers.
Examples from Nature
- Social Amoebae (Dictyostelium discoideum):
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- These unicellular amoebae aggregate into multicellular structures when food is scarce.
- About 20% of them altruistically sacrifice themselves to form a stalk, benefiting the remaining 80% (which become spores).
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Other Examples:
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- Worker bees, meerkats, and even humans exhibit altruistic behaviours driven by similar genetic mechanisms.
- Beyond Altruism: The Dark Side of Green-Beard Genes.
- Spiteful Behaviour:
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- Some green-beard genes may lead to harmful behaviour toward individuals lacking the same gene variant.
- The same gene can either promote cooperation or conflict, depending on the context.
- Evolutionary Implications:
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- Green-beard genes challenge traditional theories like kin selection.
- They provide an alternative explanation for altruism that doesn’t solely rely on relatedness.