Hi. It's Paul Andersen. And this is disciplinary core idea LS3A. It's
on the inheritance of traits. It's really on genetics. And genes are simply made of
DNA. And so inheritance is how we pass our genes from one generation on to the next.
And so this is a picture of my family. This is my dad. My mom. My two sisters. This is
my brother. And this is me. And if you look at me, I look different from my parents. But
there are similarities as well. And I owe all of that to my chromosomes. And so sometimes
students struggle with what's a chromosome, gene, DNA, nucleus. All of that. So let me
lay that out. First of all we have a cell. And so in a typical organism that's eukaryotic
like us, you're going to have nuclei. And inside the nuclei you're going to have number
of chromosomes. We have 46 in humans. If you take that chromosome and unravel it what you'll
find is that there are sections of it. And those are called genes. But the whole entire
thing is made up of DNA. And so the DNA itself is made up of what are called nucleotides.
And these are sometimes referred to as the 4 letters of DNA. And so again, to go backwards,
the nucleotides make up the DNA. A single stretch of that DNA is called a gene. And
then all of that is raveled up into a chromosome. And we have lots of chromosomes inside us.
And so what do the chromosomes do? Well number one, they're a blueprint for how to make an
organism. So they're the directions on how to make a human. They also however are important
in inheritance. In other words the chromosomes are going to be what you pass on to the next
generation. And it's what your receive from the generation before you. And so let's get
to the blueprint part first. And so how is it the blueprint for an organism? Well again,
a section of DNA is going to be a gene. It's a number of different nucleotides, a number
of different letters in a specific order. And so what are cell does is it will convert
that DNA which sits safely in the nucleus into something called messenger RNA. And that
process is called transcription. So it's really like writing down a recipe. And then it's
sending it out to the rest the cell. And the machinery of the cell is going to convert
that message or that messenger RNA into a protein. And so when you're looking at a human,
when you're looking at me right now what you're really looking at are proteins. Or things
that are a result of protein action. And so my skin, my hair, my nails, my muscle, my
bone, they're all made up of different proteins. And those proteins come from the DNA itself.
And so really if we go through this order in yourselves, DNA makes messenger RNA. That
makes proteins. And then the proteins make you. And so your DNA is not that amazing.
All it is is it's just a copy of the directions on how to make a new you. Now as cells copy
themselves they have to make sure that the DNA is copied to each cell. And so the DNA
before a cell divides is going to replicate or it's going to copy itself right in half.
And what's neat about a double helix is that it can unzip in the middle and then we can
add the complimentary letters. And then we have two new strands of DNA. Or we've copied
the chromosome. After we've done that the chromosomes will kind of coalesce and then
we divide. And so as the cell divides it's splitting those chromosomes into the two cells.
And then this can occur over and over and over again. And so the DNA in all of the cells
of you body is identical. And it came from all of the DNA that was in that first fertilized
egg. And so how do we get to the inheritance part? Well you're passing on half of your
chromosomes to your offspring. And so in sexual reproduction, that's what humans use, you're
getting half of your chromosomes from your mom and half of your chromosomes from your
dad. And so you are like your parents. You have half of their DNA, but you're also different
from your parents. And that's because you're getting a random half of the chromosomes from
each of your parents. And so what is a population? A population be it of lions or ants or chimps
or aspen trees, it's all going to be created through inheritance. Inheritance of DNA. And
all of these lions look very similar, but they also look different. And they could owe
inheritance to that. So how do you teach this? What's the teaching progression? Well in the
lower elementary grades you should talk about offspring. So offspring that are created by
parents. Be it a tree or a humming bird or you. And you want to emphasize this point.
That they're similar. And so if you look at these three birds, they all look like humming
birds. There are going to be similarities in there, but their offspring is going to
be slightly different than the two parents. Just like this small sapling is going to be
similar to the tree that created it or the trees that created it. But it's going to be
different as well. And this baby is going to be very similar to mom. In fact 50% similar.
But it's also going to be different. And each generation is getting genes. But it's also
mixing those genes up. And so we get variation within each generation. As you move into the
upper elementary grades you want to talk about how we're created. We're created by our parents.
And so they're giving us each a half a set of their chromosomes. And that's making us
the way we are. But our environment is also shaping who we are as well. And so it's not
only the nature, in the other words the DNA that we get from our parents, but it's the
nurture. It's what happens to us during our life that shapes us and gives us the characteristics
that we have. And so for example the food we get, the nutrients we get. The chemicals
that we're exposed to are going to change us as an individual. And then the experiences
that we have in our life. Learning for example is going to change what we will become. And
so the DNA tells us a lot about what you're going to become, but they don't tell us the
whole picture. In fact they only tell us about half. As you move into middle school then
we want to start identifying these terms. The idea that the cell's nucleus has chromosomes.
That chromosomes are made up of a number of different genes. And the genes themselves
are made up of DNA. And then the building blocks of DNA are going to be nucleotides.
You should push this home. That humans have 23 pair of chromosomes. And so we have a chromosome
1 that we got from our mom and a chromosome 1 that we got from our dad. And a 2 that we
got from our mom and a 2 that we go from our dad. And so each of these chromosomes in humans
are going to have thousands of genes on it. And those genes, the gene you get from your
mom and the gene you get from your dad, the way they act together is going to determine
the way you look. And so for example, red hair is going to be caused by one gene. And
if you have both copies of that red gene, you're going to have red hair. Now it's not
as simple as that. Most traits are actually caused by multiple genes. And so skin color
is going to be caused by a number of just different genes that are spread across all
of your chromosomes. But that's what we're passing on to the next generation. You also
want to talk about mutations. And so if we ever have a change in the DNA then we have
a change in the messenger RNA. And then we can have a change in the protein. And so a
couple of simple mutations, red hair is caused by one change in the DNA. And blue eyes as
well. And so all people who have red hair and all people who have blue eyes could trace
their ancestor to one person who had that one mutation. And in fact all the diversity
of life had to come originally from changes in the DNA or mutations. You also want to
get more specific on what our parents are passing on to us. And so in a sperm a male
is giving half of all of his chromosomes. So he's giving 23 chromosomes to the offspring.
The mom is giving 23 chromosomes in the egg as well. And as those combine together that
creates a new organism. And that organism, if they have kids, is going to pass off half
of their chromosomes as well. As you move into high school you want to start talking
about gene expression. And that means how we make the proteins that are written in the
gene itself. And so remember a section of that chromosome is called a gene. And we can
use the directions in that gene to make a protein. This is a myoglobin protein that's
important in blood. But you also want to emphasize this. That every cell in your body has the
exact same DNA. And so the cells in my muscle, the cells in my nerves, the cells in my skin,
the cells in my eye, all of those are going to have the exact same DNA. Well how is that?
It's because you don't express all of the genes in all of your cells. And so in my eye,
I'm only expressing the eye genes. And in my muscle I'm only expressing the muscle genes.
And so the genes really only make up a small portion of our entire set of DNA. The rest
of the DNA are genes that we don't express in that specific cell. And it's also going
to be the sections between the genes which are important in gene regulation. And development
as well. And so that's inheritance. It's how you get your genes from one generation to
the next. It also is the directions on how to make a new you. And I hope that was helpful.