Hi. It's Paul Andersen. And this is disciplinary core idea LS3B. It's
on variation of traits. In this picture right here you see me and my father. And we're both
wearing our silly looking hats. And if you look at us, we don't look exactly the same.
There are clearly some similarities. But we don't look exactly the same. We're not clones
of one another. And I owe a lot of that to DNA and inheritance of traits. And so in any
population what you're going to see is variation. And so in these flowers, or in these clams
or in these moths, you're going to see variation within that population. There are clearly
going to be similarities, but there are also going to be differences. So where does that
variation come from? Well the first place that comes from are your parents. Your parents
are each going to give you half of their DNA. Of half of their genetic information. And
so depending on which half you get from your parents you literally are half of your mom
and half of your dad. We also get variation, and this is rare, but we get variation through
mutations. And so as the DNA is copying itself, as it's duplicating, occasionally it will
make mistakes. And those mistakes in the DNA can cause mistakes in you. They're not all
bad. Some of them are going to be helpful. And also you're going to get variation in
your environment depending on what chemicals you're exposed to. What foods you eat. What
experiences you have, you're going to get variation in that as well. And so really the
two important things that shape an organism are going to be the genes. The genes are going
to determine the traits for example of this moth. But it's also going to be the environment.
So the environment can shape those traits. And so it can effect development, the appearance
of an organism. It's behavior. And it can even affect its survival over time. And so
genes and environments work together to make variation. And really those are the two things
that contribute to the variation in populations. Populations like these lions, ants, chimps
and aspen trees. So how do you teach this? Well in the lower elementary grades, you want
your students looking at plants and animals and groups of plants and animals together.
And you want to first have them list all of the similarities. So can you find the similarities
in these flowers? Well the shape of the flower. They've got leaves. They've got roots. They've
got stems. And so it would be easy for your students to come up with similarities. What
about down here? What would they come up for similarities? Maybe the material that the
shell is made up of, the shape of the shell, the hinge of the shell is going to be similarities.
And then ask them to look for differences. So what are some differences you see in these
plants. And what are some differences that you see in animals? And that would be something
easy to do in a lower elementary grade. As you move on into the upper elementary grades
you want to be talking about offspring. So this is a picture of my parents offspring.
So here's my dad and my mom. And this is me, my sisters and my brother. And so where did
the differences come from? We all don't look like clones of one another. We all don't look
identical. And so where did the differences come from? They came from the parents. And
so each of the parents are giving half of their genetic information or half of their
DNA to each of the offspring. And so it depends on which half of their DNA they're giving.
And will get to that more specifically in a bit. That's going to determine what you
look like. But the environment is going to shape that as well. Nutrients you get. Experiences
you have are going to create different organism. And even identical twins, even though their
DNA is the same, they're going to be different based on environmental differences. As you
move into middle school you want to get more specific. And so males are giving sperm. Females
are giving eggs. And what they're giving is half of their chromosomes. And so they're
giving you 23 chromosomes from dad, 23 from mom. And those together create the 46 chromosomes
that make you. And so sex, sexual reproduction is going to create variation in each of the
offspring. What else can effect variation? Mutations can. So if you get changes in the
DNA, that's passed on to the next generation. That's going to cause differences in the proteins.
And it's going to cause variation. Now some of those mutations could be beneficial. So
for example skin color. Why do we have different colors of skin? It's protecting us from the
harmful UV rays. And so that would be a beneficial mutation. Sometimes we'll have harmful mutations.
Like certain types of diseases. And sometimes we'll have mutations that don't affect our
proteins at all, but they sit within our DNA. And we can use those to trace ancestry. And
then finally when we get to high school we want to get more specific in each each of
these different levels. And so our parents are giving us half of their chromosomes. But
it's not as simple as that. The process of meiosis, and we don't need to go in to super
detail with meiosis, but know this. And in this diagram we've made it much simpler. Imagine
this is two chromosomes in the parent. So they had 2 pair of chromosomes. And so what
happens in when they're passing those chromosomes off to their kid, again, they have four here.
And each of the sperm or each of the egg would only have 2. In us remember there's going
to be 46 chromosomes here. And there would be 23 in the sex cells that are created. But
something occurs right here. And what's going on is that it's crossing over. Or your swapping
chromosomes. So in this individual you're swapping some of the chromosome that they
got from their dad with the chromosome that they got from their mom. And when you create
sex cells for the next generation, you're going to do that as well. You're going to
combine the chromosome you go from your mom and your dad and you're going to send that
off to your offspring. So meiosis gives us variation. And even though you have two parents
that are going to be the same parents over time, they're going to have offspring that
are going to be greatly varied just due to meiosis. Mutations can cause change in the
offspring as well. And so as we're replicating that DNA, as we're making copies to give to
the offspring, sometimes we'll have mistakes in that. And when we get mistakes in the DNA,
be it just one letter or sometimes big chunks of the chromosomes, we're passing those on
to our offspring. So down syndrome would be an example of a chromosomal mutation. And
then finally remember the environment shapes us. And so these are two types of hydrangea.
They have the exact same DNA. Why is one blue and one is pink? It's because of the pH of
the soil. And so even though genetically they are identical, changes in the chemistry can
change their appearance. This is a Himalayan rabbit. A Himalayan rabbit is going to be
all black. And you might look at it and say not it's not. And the reason why is its DNA
is expressing a black protein. But if the temperature gets too warm, and that's going
to be in the core of the body, it won't be able to express that gene. And you won't be
able to express that black coloration. And so areas that are cooler, like the tail, the
feet and the ears are going to express the black. But the other ones aren't. And so we're
susceptible to that as well. Our environment is shaping our DNA. And things we do do to
our body effect our DNA. And we can pass that on to the next generation. And we're just
getting into this topic. It's called epigenetics. In other words you are what you are based
on your genes. But those genes can be manipulated by your environment. And so that's a lot.
But I hope it was helpful.