Question

@InYourHead
I have a few questions related to:
"Genes and Variation"

Natural selection acts directly on phenotypes.
I believe this is true right?
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When allele frequency increase in a population; does that mean the population is evolving?
Why is this?
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Genetic recombination includes the independent movement of chromosomes during meiosis as well as crossing-over.
Why is this, all it says in my textbook is nothing... It's blank.
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What are the sources of genetic variation?
My booklet says:
Mutations, Genetic Recombination in sexual reproduction, and lateral gene transfer.
(Are their anymore?)

Answer 1

Yes, natural selection does act on our phenotypes.

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When an allele frequency increases in a population,
it most likely means that the population is evolving, yes.

That is the definition of "evolution," after all.

And evolution works with natural selection.


To explain this, I'll give you a scenario:

Imagine that we're on an island.

And on this island, there are two types of birds, with these genotypes:

(A A) and (a a).

50% of the birds are (A A)
50% of the birds are (a a)

On this island, the main source of food is nuts, with hard shells.

The thing is...ONLY the (A A) birds have the ability to crack open these hard shells,
so that they can eat, and survive.

What happens to all the (a a) birds?
They starve to death,
because they cannot crack open those hard shells, in order to eat.

NATURAL selection has decided that all of the (a a) birds will die.

So, the (A A) birds get to live, right?

The (A A) birds will reproduce, and make more (A A) birds.

Over time, the population of (a a) birds, on this island, will be very few.
Maybe even 0%

And the population of (A A) birds will increase,
because they were able to survive, and reproduce.

You see?

The (A A) genotype frequency increased.
And, of course, we know that genotypes are formed with alleles.

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Answer 2

Genetic recombination is where genes are broken up,
and then recombined, into new forms of genes.

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Imagine this:

You and I both have two toy buildings, made of little tiny Lego pieces.

Your building is made of BLUE pieces.
My building is made of RED pieces.

Alright?

Now, imagine that we both take apart our toy buildings,
so that we each have a pile of little Lego pieces.

And then, we take our piles of Lego pieces,
and we combine it all into one big pile.

This big pile has both RED and BLUE Lego pieces in it, now.

And then, imagine that we REBUILD our toy buildings,
using Lego pieces from that big pile.

Now, my toy building would be made up of BOTH RED and BLUE Lego pieces.
And your toy building would also be made up of both red, and blue Lego pieces.

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This is how we can imagine GENETIC RECOMBINATION.

It's where genes are broken up,
and then RECOMBINE, into new forms.

And it happens during Meiosis.

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CROSSING OVER is what I'm talking about.

Toward the beginning of meiosis,
the chromosomes that you get from your MOM,
and the chromosomes that you get from your DAD
both wrap around each other.

And when they wrap around each other,
bits and pieces, from each of them, get broken off,
and glued onto each other.

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After crossing over,
we have something called INDEPENDENT MOVEMENT (which relates to "independent assortment.)

The chromosomes are all getting ready to be pulled apart, by spindle fibers.

Some of them will get pulled to the LEFT side of the cell.
And some of them will get pulled to the RIGHT side of the cell.

BUT before this happens,
the chromosomes have to line up in the middle of the cell.
Remember?

Well, this is where INDEPENDENT MOVEMENT happens.

When the chromosomes line up, in the middle of the cell,
they line up in a RANDOM FORMATION.

You can never tell which chromosomes will be moved to the RIGHT,
and which ones will be moved to the LEFT,
because it's all RANDOM.

Answer 3

I wouldn't call it "genetic recombination" though.

It would be more accurately said as "Gene Shuffling," I think.

Answer 4

Mutations, Genetic Recombination, and Lateral Gene Transfer
are the three main sources of genetic variation.

There aren't any more that I know of.

Answer 5

I've never heard of "lateral gene transfer,"
but I'm sure it also goes by the more familiar name "gene flow."

Answer 6

one of a kind ^

Answer 7

He's better than my teacher. ^_^
@InYourHead thank you, I understand now :)

Answer 8

It's no problem.