Pleiotropy occurs when one gene influences two or more seemingly unrelated phenotypic traits. (from Wikipedia)
(from Greek πλείων pleion, "more", and τρόπος tropos, "way")
Pleiotropy is a relatively obscure word but it is a concept with very deep implications. Some define is using "unrelated" and some "seemingly unrelated" and this itself illustrates the difficulties in understanding this concept.
There are 3 fundamental commonalities of biological systems that relate to pleiotropy:
1) Due to the economy of evolution by natural selection, components of systems and the systems themselves systems are multi-functional.
2) Due to advantages mediated by group interactions, components of systems and the systems themselves systems are interdependent.
3) Due to advantages mediated by group interactions, some proportion of beings are interdependent intra-specifically and extra-specifically.
We would like to affect desirable changes in the our evolution and the evolution of the beings we attempt to manage (crops, livestock, pets...). We have done this through selective breeding currently and in the past, and are focusing effort to do this is a directed focused manner currently though biotechnology.
Managing the our evolution and the evolution of the beings we manage is a brutal ugly endeavor. This oppositional process generates immeasurable amounts of suffering. The natural process is little better. The wild process is little better.
Natural or directed, efforts to control evolution are complicated by both pleiotropy and genetic bottlenecking. Both have left huge scars on mankind and the beings we try to manage.
Anything we actively or passively select for or against, will also actively or passively select for or against other traits and tendencies. These silent passengers may not manifest until certain environmental, dietary or social conditionals are met.
A readily observable example of this can be seen in "pure-bread dogs". Purebred dogs have a group of observable and silent traits associated with the breed, that make it readily distinguishable from other breeds. The amount of suffering, inbreeding, and bottle-necking that went into making these breeds is unimaginable. Now we have purebred dogs that look striking, are suited to certain tasks, and are relatively healthy when they are young. These are the criteria dog breeders chose when crafting the breed. These purebred dogs may breed "champions" but overall they are unhealthy at every age, and simply fall apart as they age. When we made purebreds there was a lot of baggage due to pleiotropy and genetic bottle-necking that came along for the ride.
We are currently engaging in intense directed and natural selection for privileged positions in human societies. We design complex testing systems people must compete to even be tested, and then must win to gain "advantage", all with the illusion of objectivity. But there is little objectivity and very specific traits are being selected for. The conditions we impose and those we give advantage to will have pleiotropic effects both on individuals and society.
Long term survival is is a balance between leveraging short and medium term advantages while at the same time maintaining enough diversity and flexibility to pass infrequent/random environmental or social conditionals which can present at any time. Even huge advantage and numerical represntation in a given environment and time means little if an environmantal conditional presents the day later that a species cannot pass and leads to extinction.
Animal and plant breeders are well-versed about pleiotropy. They know that increasing growth rate or improving another phenotype is of little value if that adversely afects viability, disease resiatance, or reproduction. They also know that sometimes the appearance of seemingly unimpornat trait indicates that the animal or plant has a desired triat (e.g., flower color and toxin in the seed of cotton). A geneal discussion for fish can be found in Genetics For Fsh Hatchery Managers (p 67-72). I cannot tell you if ecologists or other field biolgists understand the implication of pleiotropy, but those who breed captive popualtions do.
Yes, breeders past and present have some subset mastery of pleiotropy.....
Its understanding is a great tool in selection and to encourage local or indigenous desired breed.
I believe the understanding will help the evolutionary world and all life science researchers
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