Jump to content
Join the Unexplained Mysteries community today! It's free and setting up an account only takes a moment.
- Sign In or Create Account -
Sign in to follow this  
thaphantum

How Exactly Do They Date Fossils?

52 posts in this topic

Recommended Posts

J. K.

Pigment on the other hand, is much cheaper to make and has less negative costs associated with it than eyes--Ergo, eyes are lost before pigment.

Still trying to work through these ideas.

I know that cave-dwelling organisms are presumed to have lost their eyes since they are not needed in darkness. But didn't you say that from generation to generation there is merely a change in alleles? So wouldn't the loss of eyes result from the loss/corruption of the allele, rather than non-usage of the eye? Wouldn't that make the loss random, rather than a cause/effect relationship of unnecessary energy expenditure?

Share this post


Link to post
Share on other sites
 
Copasetic

Still trying to work through these ideas.

I know that cave-dwelling organisms are presumed to have lost their eyes since they are not needed in darkness.

You're thinking too small and in human terms. Its not just "eyes weren't needed", its the myriad of reasons that having eyes imparts a negative cost to fitness in those niches.

But didn't you say that from generation to generation there is merely a change in alleles?

Yes, sort of. Allele frequencies change from generation to generation--That is the biological fact of evolution. What drives this change, for the most part (at least thinking about it as a novice of biology) is natural selection (caveat; There are more drivers of evolutionary change than just NS, but adding those to the discussion at this point would probably confuse you or other already confused readers. In this regard its good to build your knowledge like a pyramid with a strong base: and at that base of evolutionary biology is understanding natural selection).

Now, you told me you weren't so hot at math and I've ran into this problem before with the word frequency, so I want to take a minute to elaborate on what it means.

For a population, we can think about all the alleles present and call that their "gene pool". So lets tread lightly on some math then, suppose we have a gene which encodes a protein in a population. We'll call this the "Q" gene. And in the population their are two "flavors" of the gene (what we call alleles). Lets say that one encodes with a serine at position 19 in the protein, while the second flavor encodes a threonine at position 19--And we call each "flavor" Q and q, respectively.

Now suppose this population is diplioid, like us (meaning they have 2 copies of each gene). It is then possible to have individuals who's genotype is;

QQ

Qq

qq

Follow me so far?

Now suppose we actually went out and surveyed all the members of the population. Let's say, for simplicities sake there were 1,000 individuals. We took a blood sample and went into the lab and ran a Southern Blot (a type of assay that allows us to "read" the DNA) and find the following results;

300 individuals with the genotype QQ

500 individuals with the genotype Qq

200 individuals with the genotype qq

From that we can compute the frequency of each allele (Q or q) in the population. We see that there are 600 (from individuals Q and Q) + 500 (from individuals Q and q) for a total of 1100 Q's.

The frequency of Q in the population then, is 1100/2000 (why 2000 and not 1000? Because the population is dipliod which means each individual has 2 copies of the gene), or .55

While the q allele has a 900/2000 (from 500+400) or .45 frequency.

Now lets add a twist. Suppose that our population recently migrated to a new environment and in that environment having a threonine in place of the serine (meaning you have the q allele) you were less reproductively successful than having the Q allele. So much so, that individuals with 2 Q alleles out reproduced those with 1 Q allele 4-fold, while individuals with 1 Q allele out reproduced those with none (only 2 q's) 2-fold.

Our population after the next generation might now look something like this;

500 with QQ

400 with Qq

100 with qq.

Our new frequency of Q then is; 1400/2000 or .70

and new frequency of q then is; 600/2000 or .30

So that's what we mean when we talk about change in allele frequency. To develop a complex organ like an eye, we are talking about hundreds of genes with thousands of alleles involved. So obviously, its much more complex than the the simple 1 gene, 2 allele system we've used as an example above. In reality selection doesn't act on lone alleles, but rather often combinations of alleles.

So this is a very important point and one you need to understand about evolution; evolution works on populations like described above. This is "why" individuals don't evolve (their alleles are fixed) and "why" you don't magically need two new "firsts" in evolution to have interbreeding. Because we are talking about changes either through sexual recombination of existing alleles or mutations (which introduce new variation) that don't change individuals so much they are unable to still reproduce in that population.

So wouldn't the loss of eyes result from the loss/corruption of the allele, rather than non-usage of the eye?

The loss of the eyes would result reduced frequencies of alleles which "say" "make eyes". Now there are lots of in depth (genetically speaking) this can happen. You can have mutations which inactivate a gene, such that the protein no longer works or is made. You could have an activating mutation which turns on a regulatory gene which always regulates something to "off". You could have new alleles which "say" to make a membrane over the eye in question (as seen in some cave species), etc.

And all those would provide a positive selective benefit to the organism's fitness for a variety of reasons, more than just "non-use".

Wouldn't that make the loss random, rather than a cause/effect relationship of unnecessary energy expenditure?

No. This is again an important point about evolution by natural selection. It isn't random. Selection is non-random. Remember I said it is differential survival and reproduction. That means the chance each individual has in a population, to survive OR reproduce isn't the same. The chances for each individual are NOT equiprobable (the same), which is what it would be if it were random.

Just like in the example above where individuals with 2x Q's had a greater reproductive output of 1x Q. And individuals with 1x Q had a greater reproductive output than individuals with no Q's. Just like in real life where certain alleles or combinations of alleles make an individual more likely to survive and more likely to reproduce.

Understand that?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.