Hi everyone, and welcome to Biology Professor.
Today, we're talking about the Law of Independent
Assortment.
Now, the inheritance of biological features,
which we now know are genes, follows laws
that were proposed by a man named Gregor Mendel
in the 1860's.
Mendel worked with pea plants and determined
three laws regarding patterns of inheritance.
These are the Law of Segregation, the Law
of Independent Assortment, which is what we
are talking about today, and the Law of Dominance.
Now, if you are interested in learning more
about the Law of Segregation or the Law of
Dominance, see my other videos on those topics.
But now for the Law of Independent Assortment.
It states that genes for different features
segregate independently during gamete formation.
For example, when gametes are formed (this
means egg cells or sperm cells in humans),
traits that control different features separate
into gametes independently of each other,
so the inheritance of alleles for hair color,
eye color, skin color, height, et cetera,
all of these physical features, they don't
affect each other, so they separate into gametes
independently from each other.
So, for example, in Mendel's classic example
with pea plants, seed color, you have alleles,
alternative forms of genes, so you have an
allele for the seeds being yellow or the seeds
being green, which is the other allele.
Also seed texture, there's an allele for the
seeds being smooth and another allele for
them being wrinkled.
And these things segregate independently into
gametes, so the alleles for seed color don't
affect how the alleles for seed texture are
inherited.
Now, this Law has a couple of caveats.
It is true only for genes that are on different
chromosomes.
Of course, Mendel did not know what chromosomes
were.
When Mendel was working, it wasn't even known
yet that DNA was the genetic material in cells.
But now we know that it is true only for genes
on different chromosomes because chromosomes
themselves sort into different gametes during
meiosis, and it's also true for genes that
are far enough apart on the same chromosome
to be separated during meiosis by a process
called recombination.
Recombination occurs when homologous chromosomes
line up, and this is during prophase I of
meiosis, and then they have a crossing over
event.
So you can see that alleles that have once
been on the lower edge of this chromosome
are now on the lower edge of this chromosome
and vice versa.
So this is what happens during recombination.
You have genetic material switching from one
homologous chromosome to the other.
Of course, then these homologous chromosomes
are spread apart into sister chromatids in
meiosis I.
Those sister chromatids are then split apart in meiosis II, so you get gametes that will
have one of these four chromosomes.
So you can see that with recombination happening one to three times per chromosome, you can
get a lot of variation happening that way.
And also, if we go back to talking about the Law of Independent Assortment, if you have
genes that are far enough apart on the same chromosome, they can be separated by recombination.
For example, if you have a gene up here and a gene right here, well after recombination,
where are those alleles?
You've got one here and the other one here and then they will segregate into different
gametes, that is the Law of Segregation.
Now if you are interested in learning more
about the Law of Segregation or the Law of
Dominance, remember to see my other videos.
But that's it for the Law of Independent Assortment.
I hope you learned a lot and thanks for watching.
