What's a "bottleneck"?

[Pembleton]

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It has something to do with speciation but I can't find it in Bio textbook.

Appreciate the help.

 

[ASDIC]

a bottleneck is a result of a natural or an artificial catastrophe that alters the genotypes present in the surviving population.

So for example, if you had a population of polar bears in alaska with Long legs (dominant) and short legs (recessive), and lets say there was an arctic storm one night that wiped out a huge number of long legged polar bears, the short legged polar bears will be the survivors. And the allele for short legs would become the dominant allele. So in fact the short legged bears bottlenecked or squeezed as the majority.

 

[antissa]

It's when a big population suddenly loses a lot of members and becomes small, thereby losing diversity. When the surviving members replenish the population, it tends to be more homogenous than before

 

[bella_dottoressa]

Ok going from memory here...

A bottleneck is when you have an event that severly alters the genotype/phenotype frequency of individuals in a population by dramatically decreasing the number of individuals in a popultaion. So, say you have a population of birds and a big volcano erupts and it kills 75% of the birds. Now say that a third of those birds were red, a third were pink, and a third were white. It's unlikely that exactly a third of the 75% of birds that die are going to be red, a third pink, etc. More than likely this catastrophe is going to alter the allele frequencies in your population, i.e. leave a disproportionate number of red birds for instance. Hence a population bottleneck. Basically, your population is reduced dramatically in size for a certain amount of time and this alters the gene frequencies in the population so when the survivors reproduce again the allele frequency is going to be changed in the population.

 

[Pembleton]

Excellent answers all!

Thanks a lot.

And for your generosity, I pray your BS scores exceed your expectations!

 

[MDtoBe777]

So when does Hardy-Weinberg equilibrium end up returning allele frequencies back to normal. Oh wait, that means you need a population that follows H-W equilibrium right? So in this case, there is a bottleneck which clearly violates H-W equilibrium. So H-W doesn't apply here? Is this right?

 

[Doc.Holliday]

So when does Hardy-Weinberg equilibrium end up returning allele frequencies back to normal. Oh wait, that means you need a population that follows H-W equilibrium right? So in this case, there is a bottleneck which clearly violates H-W equilibrium. So H-W doesn't apply here? Is this right?

yep...

 

[bella_dottoressa]

No populations really ever follow H-W equilibrium. It's like a null hypothesis; something we can hold real populations up to to better understand them by how they differ from a population in H-W equilibrium. All real populations are going to break some of the tenets of H-W.

 

[MDtoBe777]

So when would a population return to the values expected by H-W equilibrium? I read in TPR that this happens after 1 year.

 

[Doc.Holliday]

returns to equilibrium after what? if its a bottleneck that wipes out an allele it will never return unless somehow that allele is reintroduced into the pop...

 

[safrat]

I wanted to add this bit of info. Sometimes people refer to a bottleneck in the reverse shape of what has been defined. What I mean by this is that instead of it just eliminating a phenotype/genotype, I've also heard it used describing the sudden outbreak of species from a small gene pool--Cambrian Period. I think that's the period.

I think the term itself is used in the descriptive-literal sense. In comp. sci., we use it to describe any situation which involves a lot of data going through a small space. This small space would create a bottleneck; hence, the name bottleneck.