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Could someone help me out with a basic example of the interactions of 2 or more non-identical alleles leading to an advantageous outcome for an individual organism? Based on empirical research OR on a theoretical model.

An example of 2 or more non-identical alleles cooperating across replication iterations/generations between individual organisms would be even beter. I somehow find this more spectacular :)

Please let me know if I'm not mentioning enough elements to answer the question. It's a very broad question and I accept very broad answers - semantically and across scientific branches.

All the best,


Personal background: I am new to the scientific field of biology. I think I caught up on some of the basic principles of genetics, allellomorphs, loci and DNA replication and I've gotten interested in the workings of alleles.

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I don't fully understand your question for two reasons. 1) When you say an example do you mean an empirical observation or do you mean a theoretical (mathematical and/or logic/intuitive) model? 2) You're interested about a case where 2 alleles cooperate. You mean, you have two bi-allelic (to keep it as simple as possible) genes and for each gene one allele is causing the individual carrying it to produce a helping behavior? – Remi.b Jan 18 '14 at 13:42
Or a helping behavior only restricted toward individuals that carry the right allele of the other gene? Or do you mean, if two genes, A and B which alleles are A1, A2, B1 and B2. If one individual is A1B1 then this individual has a high fitness advantage. Any other combination does not provide any fitness advantage. Something like this? Or do you mean anything else? Could you please give a better description of what you mean by "allele that cooperate". – Remi.b Jan 18 '14 at 13:43
Thank you for revealing some of the ambiguities of my question to me. I admit my question is open to different interpretations and not well specified. I have edited the question to address your comments, although not to the full extent. – hamburger Jan 18 '14 at 14:53
up vote 1 down vote accepted

Reading your updated question, I think you are interested about epistasis. Let me know if I am mistaken.

The concept of epistasis might be confused with the one of pleyotropy, so I will define both terms.

Pleyotropy occurs when one gene influences multiple phenotypic traits. Note: the phenotype, to make it simply is what a living things look like (its cells, proteins, shape of the face, size of the leaves, etc…). It is often thought in duality with the genotype which is the total genetic information contained in an individual that codes for the phenotype (Be careful, the environment is also an important factor influencing the phenotype, if you make sports you will have big muscles!)

Epistasis is when the effect on the phenotype of one gene depends on the presence of several (or only one) other genes. Wikipedia gives this (simplistic) example:

enter image description here

Here, two bi-allelic genes are involved. One gene that determines the hair color. The two alleles influence the phenotype such: one allele gives red hair and the other allele gives blond hair. Now There's another bi-allelic gene coding for baldness. One allele causes the bearer to be hairy and the other one causes the bearer to be bald. Therefore, if an individual carries the allele "Bald" in the "Baldness" loci, what this individual carries on the other loci is not important because it will result into the same phenotype anyway, he is bald. Now if in the baldness loci, the allele is "Hairy", then the expression of the other gene "Hair color" matters and therefore if the allele is "blond", the bearer has blond hair and if the allele is "red" the bearer has red hair.

The "Baldness" gene is called a modifier. One can also say that the expression the "Hair color" gene depends on the genetic background of the individual.

Now cases of epistasis are not always that easy and if they influence the fitness, this kind of epistatic interaction might have implications for their evolution.

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awesome - it looks like a fitting example - I'll study epistasis and pleyotropy in the near future (added to my to do list) – hamburger Jan 18 '14 at 15:34
;) Great! I would recommend to avoid using the word "cooperation" for such interaction. Cooperation in evolutionary biology is linked to the concept of altruistic behavior. Therefore, cooperation is a word that mostly stand for relations at higher level, between individuals (or between cells) and not between genes. The evolution of altruism is a big field of evolutionary biology (social evolution, evolution of multicellularity, level of selection,…) that is still on debate. – Remi.b Jan 18 '14 at 15:40

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