Green-Beard Genes

Theoretical concept of the Green-beard genes could explain the reason, as to how the universal virtue of altruism arose in nature.

Green-beard Genes – Theory and Reality

• The sample amoebae: Researchers used the amoeba species, Dictyostelium discoideum for the study.
  • It is a free-living, fast-growing, unicellular amoeba
• Studies: 
  • The UK study: A 2017 study by the researchers from the University of Manchester, U.K., reported that two genes, namely,  tgrB1 and tgrC1  in the D. discoideum genome displayed all the properties of a green-beard gene. 
  • The USA study: A 2024 study by the  researchers of the Baylor College of Medicine in the U.S. reported evidence that D. discoideum amoebae use these green beard genes to navigate the risk of chimerism.
• Published In: Both the studies were published in the journal Nature Communications.  

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• Process:
  • Researchers fed  the amoebas a bacterial ‘lawn’ grown in a Petri dish in a laboratory.
  • Formation of aggregates: The amoebae stop multiplying and gather together to form multicellular aggregates when the bacteria run out, The aggregates then transform into fruiting bodies, each a few millimetres tall. 
  • A fruiting body: It is composed of a slender stalk made of dead cells, and it holds aloft a droplet of spores. About 20% of the amoebae in an aggregate altruistically sacrifice themselves to form the stalk. The remaining 80% become the spores.
  • The cycle: Small fauna, such as ants and earthworms, disperse the spores to new food sources where they germinate to release amoebae. The newly released amoebae then go on to repeat the cycle of growth, division, and dispersal.
• Findings: 
  • The tgrB1 and tgrC1 genes: They  are located next to each other in the D. discoideum genome, and are expressed together.
    • They contain information for cells to make two cell surface proteins called TgrB1 and TgrC1.
    • Binding: The TgrB1 protein on one cell binds to the TgrC1 protein on another.  If the binding is strong, the TgrB1 protein is activated, and confers altruistic behaviour, manifested as the amoeba’s willingness to form the stalk.
    • The binding between the TgrB1 and the TgrC1 proteins of cells of the same strain is strong, and leads to self-recognition and cell-cell cooperation. 
  • Self- Recognition: It is postulated that the  green-beard genes encode some kind of tag that helps the genome to know their identity 
  • The green-beard genes allow the individuals bearing them to recognise and preferentially cooperate with each other.
  • Selfish behaviour towards other genes: Alternatively, a green-beard gene could provoke individuals to behave harmfully towards those carrying a different version of the gene.

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