Notes S ; Selectiedruk
september 29, 2013 1 reactie
Selectiedruk is in de evolutiebiologie het effect dat de natuurlijke selectie uitoefent op de genetische variatie of genfrequentie binnen een bepaalde populatie van een soort(species ) . Bepaalde eigenschappen van individuen beïnvloeden hun relatieve kans om nageslacht achter te laten. Deze interactie tussen die eigenschappen en hun omgevingsfactoren in ruimste zin heet de “selectiedruk”. Als een bepaalde selectiedruk geacht wordt aanwezig te zijn, impliceert dat een overeenkomende verwachting ten aanzien van de verandering van de genfrequentie, ofwel de evolutie.
Invloed van milieufactoren, waardoor genfrequenties veranderen.
Gevonden op http://www.digischool.nl/bi/pbb/search.php
Selectiehandvat ….de genetische varianten in een populatie die in een bepaald millieu de betere (hoe klein die ook mogen zijn in vergelijking met het geheel van de populatie ) verwachte overlevings en voortplantingskansen (fittness) bezitten
Any cause that reduces reproductive success in a proportion of a population, potentially exerts evolutionary pressure or selection pressure. With sufficient pressure, inherited traits that mitigate its effects – even if they would be deleterious in other circumstances – can become widely spread through a population. It is a quantitative description of the amount of change occurring in processes investigated by evolutionary biology, but the formal concept is often extended to other areas of research.
(Microbiology ) Any cause that reduces reproductive success in a proportion of a population, potentially exerts evolutionary pressure or selection pressure. (wiki)
Examples of selective pressure in the following topics:
SELECTION PRESSURE is any phenomena which alters the behavior and fitness of living organisms within a given environment. It is the driving force of evolution and natural selection.
Environmental conditions leading to differential fitness based on the value of any particular trait …– the pressure of competition to survive and have surviving offspring. The word “selection” refers to the fact that some variants (the “fittest”) are better at doing this than others.
“THE PRESSURE OF SELECTION ”
“Selection pressures” is a shorthand term for something a bit more complicated.
—it is a metaphor, a descriptor of what happens when different genes (i.e. “alleles”, or forms of a single type of gene) leave different number of copies. That differential reproduction of genes is what constitutes natural selection,, and it is a process of gene sorting.
There are no “pressures” of selection imposed on the organism from the outside.
What happens, as everyone knows who learns introductory evolution, is that, in a given environment, some genes leave more copies than others, usually because they increase the reproductive output of their possessor.
Take, for example, a population of brown bears that somehow find themselves in a white-colored environment, like the Arctic.
There are genes affecting coat color, and imagine that a given gene comes in several forms, one of which makes the bear lighter in color than do the alternative forms. This being a population of bears, there will be variation among their genes due to mutation. Those bears carrying the “light” forms of genes might do better than their browner confrères because they’re more camouflaged in the snow, and thus better at sneaking up on seals and killing them. “Light-gene” bears will be better fed, and thus have better survival and (crucially) more offspring. (If the color change affects survival but not reproductive output, no natural selection ensues.) In the next generation, the proportion of color genes having the light form will be higher than before. And the average color of the bear population will be a bit lighter.
If this continues over many generations, and other mutations occur that yield even lighter coats, natural selection will move the bears from brown to white. Presumably this is what happened in polar bears, whose ancestors were probably brown. And it’s happened in many Arctic animals whose ancestors were brown but evolved white color (either pemanently or seasonally) via natural selection.
Such animals include the Arctic fox, the Arctic hare, the ptarmigan, the snowy owl, the harp seal, and so on (see a list here).
Note that the environment isn’t exerting any “pressure” here. It is simply providing a milieu in which one gene has an advantage over another. The environment cannot see the genes and their constituent DNA.
We speak of “selective pressure to become light-colored” as simple shorthand for the process I’ve described above.
—> Is the use of metaphors confusing ? Metaphors are useful if as they enlighten rather than confuse.
–> I claim that both “selection pressures” and “selfish genes” are enlightening,
—>The term “laws of physics” is also a metaphor, or a enlightening shorthand descriptor. There are no “laws of physics,” but just regularities in the universe that appear to be ubiquitously “followed”.