Lesson video

Welcome to this lesson from the unit Heredity and DNA.

The title of today's lesson is DNA, chromosomes, genes and the genome.

Now, these are all key terms that you may have heard of before.

What we're going to do today is we're going to work through them and we're going to talk about how we use them to describe how DNA is packaged and what it's used for within a living organism.

My name's Mrs. Barnard, and I'm going to be taking you through today's lesson.

So by the end of today's lesson, you should be able to explain the difference between DNA, chromosomes, genes, and the genome.

So some of those are our keywords and there's a couple of others.

So our keywords today are genome, DNA, nucleus, chromosome, and gene.

So I'm going to put up the definitions for you.

So you can either copy these down in the back of your books or we will circle back to them later in the lesson to give you a definition, but you can pause the video now if you'd like to do that.

So our lesson today is in three parts.

Part number one is the genome, part number two is DNA and chromosomes, and part number three is genes and other parts of the genome.

So we're going to start today's lesson with the genome.

So let's get started.

So the genome is something that all living organisms have, and it's all of the genetic information of a living organism.

And here's some images of living organisms, just to remind you that living organisms aren't just animals, they're also fungi and plants and bacteria.

And inside all of those living organisms, we have DNA that is stored in the nucleus of their cells.

So we've got bacteria in that picture there, those red bacteria that are swimming along and they are, remember, single-celled and they actually keep their DNA in their cytoplasm.

But all of those other organisms there are made of cells that store their DNA in the nucleus.

So what I'd like you to do is to complete the definition, all of the genetic material of a cell is called what? Is it A, the genes; B, the DNA; C, the features; or D, the genome? Okay, have you decided? So the answer is the genome.

All of the genetic material of a cell is called the genome.

But what's the job of the genome? Well, the genome codes for all of our inherited features and the processes of living organisms. It's like an entire instruction manual for a living organism.

And that is because we've got a long DNA molecule here, and within that long DNA molecule, it's made of smaller chemical units.

Scientists call these A T, C, and G and they make up the genetic code.

Now, the genetic code depends on the sequence of those smaller chemicals, those A, T, Cs, and Gs, like the letters of an alphabet, if you put them into different combinations, make up words.

Those different letters, if you put them in different combinations, can give you different features, but also control different life processes.

So all organisms on Earth actually have similarities in their genome sequence.

The reason is because we're all living.

So therefore we all carry out some of the common processes of living organisms, and those are controlled by the instructions held within our genome.

Differences in our genomic sequence though make us unique.

So the thing that makes us different from one another and from other species is differences in our genome.

So members of the same family have the most similarities.

That's probably what you would expect, because you share more of our physical features and inherited processes that are similar to those in your family.

If you're part of the same species but you are unrelated to each other, so different families, you still have a lot of similarities because you belong to the same species, but not as many as if you're closely related in the same family.

And then members of different species will also share quite a lot of their genome sequence.

However, there's more differences between different species.

Let's have a little look at some of the numbers for how much of our genome sequence that we share with other organisms. So humans and all other humans share 99.

9% of their genome sequence.

That means the things that make us different from one another is only 0.

01%.

So not very much at all that makes us different from each other.

What about the next living organism that we are related closely to? You might have already known that that is chimpanzees.

And we actually share 98% of our genomic sequence with a chimpanzee.

That's a lot, isn't it? But if you think about it, they look quite similar to us.

They've got similar body plan, okay? They live in family groups, they have lots of their life processes the same.

So therefore you would think that we would share quite a lot of our sequences.

However, 98% is a large number.

Wonder if you can have a guess how much humans and chickens share in common.

I'll give you a minute to have a suggestion to the person next to you.

Okay, so it is 75%.

So 75% of our genome sequences are the same as a chicken.

Again, remember, they are an animal.

They carry out lots of the same processes as us, and they are warm-blooded.

So we are quite similar to chickens, more than you might think.

So if we go down the list further, humans and fruit flies, 60%.

So you wouldn't believe that more than half of your DNA or genome sequence is the same as a fly.

And we get all the way down here to daffodils.

So daffodils are plants, okay, flowering plants.

And we share 30% of our DNA, our genome sequence is the same as those, and that is because they are living organisms so they carry out a lot of the same life processes us.

So if you remember things like respiration, excretion, nutrition, growth, all of those things are controlled by instructions that are held within our genome.

So let's have a quick check.

Starting with the most similar, put these things in order of how similar their genomes are.

So the three options you've got are: members of different species, members of the same family, or unrelated members of the same species.

So put those in order and then we'll come back and check how you got on.

Okay, so starting with the most similar, we have members of the same family.

So they would be the same species, but the same family within the same species.

Next one, we have unrelated members of the same species is second.

And then finally we've got members of different species would be third.

So hopefully you've got that in the same order.

So let's move on to a practise task.

So pupils are discussing their understanding of the genome.

So Laura says, "All animals have a genome." And Jacob says, "Each different species on Earth has the same genome." And Alex says, "The genome is another word for DNA." And Sophia says, "The genome is the genetic code for all of a human's features." So what I would like you to do is to improve each of their ideas by changing or adding extra detail to them.

So start where they've started and see what you can add or change to improve their ideas.

So pause the video and then we'll come back and see how you got on after.

Okay, let's see how you got on with that one then.

So we want you to improve each of the ideas of the pupils by changing or adding extra detail.

So Laura said all animals have a genome.

Jacob said each different species on Earth have the same genome.

Alex said the genome is another word for DNA.

And Sophia said the genome is the genetic code for all a human's features.

So let's see how we could improve these.

So we could improve Laura's by saying, all living organisms have a genome, not just animals, including plants, bacteria, fungi, and animals.

We could improve Jacob's by saying, all individuals of a species on Earth have a unique genome.

And those in the same species would have more similarities in their genome.

So not that they all have the same.

And for Alex, we could say, the genome is all of the DNA in an organism, not just another word for DNA.

And Sophia, we could say the genome is the genetic code for all living organisms' inherited features and processes, not just for humans.

So if you've got those corrections and those alterations right, then well done.

So now we're going to move on to the second part of our lesson, which is DNA and chromosomes.

In animal, plant, and fungi cells, all the DNA that makes up the genome is stored in the nucleus, and the DNA is organised into packages called chromosomes.

So let's have a look at what that looks like.

So we've got a picture here of a cell, and you can see that there is a nucleus inside that cell.

So we're going to look at that nucleus in a bit more detail.

And inside that nucleus you can see that there are these packages, these funny structures that have a shape that you might recognise, and those are called chromosomes.

And if you could unwind this package, this chromosome, you would see that it is made of lots of the molecule DNA.

So you've got DNA that's packaged up into chromosomes.

Those chromosomes are stored within the nucleus, and the nucleus is within the cell.

In terms of how many chromosomes you have in your nucleus depends on your species.

But for every chromosome, you have two copies of each, one from each parent.

So you have a maternal chromosome from your mother and a paternal chromosome from your father.

So we as humans have 23 pairs of chromosomes.

If you have a look at this picture here, I've drawn four pairs of chromosomes because it'd get a bit busy if I put 23 in there.

But it's the idea that every chromosome comes in a pair and one's from the maternal side and one's from the paternal side.

And we've shown that there using the colours pink and blue.

So there's our nucleus, there's inside our nucleus where our chromosomes are, and that is a pair of chromosomes.

So bacteria don't have a cell nucleus, so therefore they don't have chromosomes in pairs.

They've got one single chromosome.

So it's a big circle of DNA that is stored in their cytoplasm.

So they still have a genome, but it's not stored in those pairs of chromosomes within a nucleus.

So sections of DNA code for our features and our processes, and these are called genes.

Now, you may have heard of the word genes before.

It's a word that's used quite a lot in everyday life.

You know, passing on your genes from your parents to the children.

So genes are the things that give you your features and give you the code for your life processes.

But what a gene actually is, is it is a section of DNA.

So there's our chromosome with our DNA packaged up inside, and that's a gene, a section of DNA that will give the code or the instructions for a particular process or characteristic feature.

So true or false? Genes are made of chromosomes.

Now, once you've decided whether it's true or false, I want you to try to justify your answer with one of the explanations below.

So pause the video while you have a go at this, and then we'll come back and see how you've got on.

Okay, so what have we got here? We've got genes are made of chromosomes.

That is false.

And the reason that it's false is because genes are sections of DNA in a chromosome that code for features.

So this is your practise task.

What I would like you to do is to label this diagram of DNA storage, but for each label you need to write a brief description of that structure.

So pause the video, and we'll come back and we'll see how you've got on with your diagram soon.

Okay, did you manage to get all that done? It's a bit of a long job to label that with full descriptions.

So first of all, we've got a cell and all living organisms are made of cells.

So that would be your description for that one.

Then we've got a nucleus.

All animal, plant, and fungi cells have a nucleus.

And then we've got a chromosome.

And chromosomes, these are in pairs, and you inherit one from each parent, and humans have 23 pairs.

And then we've got DNA, and DNA is a long chemical molecule.

It carries the genetic code.

And then we've got a gene, which is a section of DNA that codes for the feature or a process.

So if you've got those labels and descriptions correct, then well done.

Let's move on.

So now we are onto the third part of our lesson, which is genes and other parts of the genome.

So genes code for features that you can see and for processes that you can't, such as growth.

So here is a section of DNA, a gene, and you can see that it can give you a feature that you can see, like eye colour, or a feature such as growth or germination, as shown by this picture of a plant.

Some sections of the genome do not code for features or processes.

These sections are not genes.

But these non-coding sections of DNA do have a job, they're found between genes, and they help to control when the instructions in genes are used.

People used to call these sections junk DNA, but it has now been found that these sections of DNA have a really important job in controlling when the instructions in those genes are used.

And in this picture you can see that the non-coding DNA is between the sections that we call genes.

So most cells in an organism carry a copy of the genome.

There are some exceptions.

And the genome is everything that is including the genes and the non-coding DNA.

So what I would like you to do now is I'd like you to match the keyword with its correct definition.

So our keywords are DNA, gene, chromosome, and genome.

So pause the video while you do that and we'll come back and see how you've got on.

Okay, let's see if we've matched these up correctly.

So DNA, the definition is a chemical molecule that stores the genetic code.

Genes are sections of DNA that code for features.

Chromosome is a package of tightly wound DNA.

And finally, the genome is all of the coding and non-coding DNA of a cell.

Okay, if you've got those right, then well done.

So let's move on with a little activity where I'm going to start an analogy for you, and I would like you to finish it off.

So an analogy of DNA organisation.

So let's say that the nucleus is like a library that stores instruction manuals.

So imagine all of those manuals stored in a library, and then imagine that the genome is like all of the instruction manuals.

So not the library itself, all of the instruction manuals that are inside that library.

And therefore one chromosome is like one instruction manual.

So let's finish off this analogy now.

So, a gene is like.

And non-coding DNA is like.

So you might want to discuss this with somebody before you come up with your answer, but pause the video and then check back.

Okay then.

So if our chromosome is like one instruction manual, and remember, our chromosomes are our DNA packaged tightly wound up, then a gene is like a paragraph of instructions that are in the manual.

So some instructions that are in a short section.

And the non-coding DNA therefore is similar, so it's paragraphs, but it's the paragraphs of the manual that don't contain the instructions.

So if you've got something similar to that, then well done, because analogies are quite hard.

Sometimes they're really good for allowing us to understand difficult ideas.

But comparing things really makes you think about whether you really understand the science.

So we've got another practise task for you here.

And first of all, we're going to start with you finding which of these statements is correct and which are incorrect.

So for each one, decide how sure you are about your answer.

So do you think it's correct or are you sure it's correct? Do you think it's incorrect or are you sure it's incorrect? So check back once you've done that.

Okay, let's see how we got on then.

So most cells in an organism have a copy of the genome.

That is correct.

Your genes and your genome are the same thing.

That is incorrect.

Genes only code for features you can see.

That is incorrect.

And non-coding sections of DNA are not useful, they're just junk.

That is incorrect.

So now we're going to move on to the second part of this task, which is, we would like you to rewrite each incorrect statement to correct it.

And those incorrect statements are written there for you.

So read what it says and then correct it.

So write a sentence that's correct but based on the same idea.

So pause the video and come back once you've completed this task.

Right, let's see how we've got on with this then.

So the first one was, your genes and your genome are the same thing, so we can correct that to: your genes are sections of your genome.

So remember, genome is all of the genetic material, whereas genes are sections of that.

Next one, genes only code for features you can see.

So the correct answer would be: genes code for features you can see and processes such as growth.

And finally, non-coding sections of DNA are not useful, they're just junk.

So non-coding sections of DNA help to control when the instructions in the genes are used, so they're not junk.

So if you've got those correct, then well done.

And that brings us to the end of our lesson today on DNA, chromosomes, genes, and the genome.

All genetic material of an organism is its genome.

Closely related organisms have lots of similarities in their genomes, and differences in the genome make us unique.

The genome is made of DNA, wound up in tightly packed structures called chromosomes.

Human body cells have 23 pairs of chromosomes stored in the cell nucleus.

Bacteria have one that is stored in the cytoplasm.

Sections of the DNA in chromosomes are called genes, which store instructions for building inherited features and controlling life processes.

Other sections of chromosomes are non-coding DNA, which contains instructions that controls when the information in genes is used.

Well done for your work in today's lesson.