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Me asked in Science & MathematicsBiology · 1 decade ago

Puzzled about mutations?

At the risk of sounding naive or even obtuse, I have to admit that there are some things about mutations in organisms that I don't get.

For example, I read that Staphylococcus aureus, owing to a mutation, developed resistance to penicillin. So, ok, does this mean that *a* Staphylococcus aureus bacteria in one particular country in one particular place developed resistance to it? How would this spread to *all* Staphylococcus aureus bacteria?

It's the same with the woodpecker's beak, another example I found in a book on evolution in discussion of mutations. It said that the woodpecker's beak gradually grew longer over successive generations of a population of woodpeckers because *a* woodpecker just happened to be born somewhere with a slightly longer beak. Natural selection then preserved this beneficial mutation and it eventually spread into the population. But how did it eventually spread to woodpeckers *everywhere*?

3 Answers

  • 1 decade ago
    Favorite Answer

    I know my anser is long, but it's pretty interesting and I tried to be a little entertaining with it. Alright, these two scenarios are a bit different, but both are based on the concept of natural selection, meaning that a trait that increases the chance of survival will continue within in the population, because an increase in survival rate usually means greater reproductive success (more offspring).

    So, your first question is about bacteria. This is latin based, but bacteria is actually plural, (sing. bacterium), so when reference is made to a bacteria, it means that a number of that type, in this case Staph, will have the resistance to the antibiotic. However, even if only one in the entire culture had a resistance, it could still work that eventually the entire culture will become resistant. This is because if one of the bacterium has the R-plasmid that contains the gene for penicillin resistance, and the antibiotic is introduced into the culture, that bacteria will survive. After it survives and all the other bacteria have died, it can grow and divide. Every time it divides, it makes copies of its genome, so every offspring will be resistant. This is how one resistant can become a culture full of them. If the antibiotic is not introduced, that one resistant bacterium can actually attach to another bacterium and give it a copy of the plasmid. This is called conjugation. So, do that a few thousand times and you have your culture of resistant bacteria. Someone gets sick with the resistant Staph and it spreads. Every time it's treated with penicillin, it will survive and multiply with no competition from its non-resistant competitors.

    Unlike bacteria, a woodpecker can't just slip its friend a longer beak gene. Therefore, a long beak is a result of a long time, probably thousands of years. So, say you have your woodpecker with its long beak resulting from a random mutation, perhaps the gene that controls beak development mutated. The trick is, however, that populations evolve, not individuals. Your woodpecker will have to have a greater chance of survival. This will allow it greater reproductive success. Let's say that that bird with the long beak is able to build its nest further inside a tree. It is out of sight from predators, while all the shorter-beaked birds are at rist for being eaten. That longer-beaked bird will hopefully make birdy love with another, and the offspring of that bird will have an allele (the copy of a trait that can be dominant or recessive, and you get one from each parent; if both are recessive, you get the recessive trait, and if at least one is dominant, you exhibit the dominant phenotype) from the long beak bird. It would help if the trait was dominant, but it doesn't have to be (6-fingers (polydactylism) is a dominant trait), so each offspring of birds that has the long beak trait will increase the survivability of the birds, until, after many, many generations, it becomes the more successful trait and spreads to other populations by breeding or mirgration or some other type of movement, random or otherwise. Eventually the longer beak will be more successful and will allow for greater numbers of offspring, and will spread so that most woodpeckers will have long beaks, and that ones that do not will not survive.

  • 1 decade ago

    There are two main things to consider here, One is selection pressure and the other is time.

    Selection pressure is how much of an advantage that the mutation occurs, so with your MRSA being resistant to penicillin, the selection pressure is huge, IF penicillin is present.

    With the woodpeckers the selection pressure is not as big as the birds with short beaks can still eat although not as well.

    So using your example lets say you have a couple of "advanced" woodpeckers in a flock of 200 (purely hypothetical i do not even know if woodpeckers live in flocks but you get the idea) , they are more succesfull in life and therefore in reproducing, so the next generation there will be say 4 long beaked birds out of around 200, in the next generation these four will again be more succesfull so there maybe 8, and so on and so on until the mutation is everywhere, and all the "short beak" alleles are lost.

    The same applies to the Staph, they divide asexually and as the selection pressure is huge. The demographic would be more like

    1st generation - 10 mutants 5000 normal

    2nd Generation - 20 mutants 0 normal (penicillin present here)

    3rd generation - 40 mutants 0 normal

    etc etc

    So you can see how easily a mutant can spread to the population

    Sorry for the long answer, hope it helps

  • 1 decade ago

    It's very likely it took thousands of years for the gene to spread, which is plenty of time for a errant woodpecker carrying the long-beaked gene to mate with a member of a "separate" population, who then introduces the beneficial trait to its population, who then spread it to the next closer population, and so on...

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