Trying to Understand Genetics

[eagerstudent082]

I am a new student to the world of genetics. Is there anything wrong with what I have written below?

 

Variation within the genepool exists; giving a species the ability to adapt to its environment.

 

For example most known birds have beaks of various shapes and sizes. The exact shape and size is determined by the alleles contained within a species' genotype. If a smaller, longer, beak is more beneficial to a certain species, within a certain environment, then this phenotype has the potential to become the favorable heritable trait.

 

Note: Go easy on me. As I said before, I am very new to this area of science.

[Mokele]

Yep, that's quite good for a beginner, and in fact the only flaw I can find is that if the small bills are beneficial, then they *are* the favorable heritable trait, not just that they have the potential to be so.

 

It also ties into the idea that for island populations, fragmented populations, large critters, inbred populations, or just about any situation where genetic diversity is low, it's harder to adapt because, well, the mutational variation you need might just not be out there.

[eagerstudent082]

It is harder for island populations to adapt because the variation needed may not be there...

 

Forgive me for asking, as I know how this question will sound, but I am asking simply to gain a better understanding. The finches observed on the isolated Galapagos islands, observed by Darwin, were very well adapted. I always assumed that it was just one original species of finch which "evolved" into the many he studied... this assumption must be wrong. Or... is there something I am missing here?

[Mokele]

It's a bit of a split, actually. If you have a small population, and a beneficial mutation occurs, it spreads very quickly. But there's also less chance of any *particular* mutation showing up at all.

 

Imagine birds on an island. That there are few mutations in the gene pool at any given time doesn't matter, since the birds are surviving just fine, and beneficial mutations just make them better at surviving. Over thousands of years, mutations come and go, with the best being selected for and becoming permanent, and those which are neutral or bad being eliminated. It doesn't really matter how long it takes for any particular mutation to show up, because the birds are surviving just fine, and until someone has a new beneficial trait, there's no inequality in fitness.

 

Now dump a new predator on the island, one which the birds have no behavioral response to - they don't just need a particular mutation, they need it now, and if nobody has one, well, bye bye birdies. Unlike before, they can't just wait a few hundred generations for it to crop up, because the new predator will have eaten them all by then.

 

Basically, small populations are vulnerable to extinction due to sudden changes, such as invasion or environmental change, which they don't have the standing stock of genetic diversity to adapt to.

[eagerstudent082]

Thank you very much for helping me out. I think I'm getting a much clearer understanding of the concepts here.

[Mokele]

Sure, that's what we're here for!