In this video I provide a basic introduction to genetics and explain genes, genomes, DNA, chromosomes, and genetic relatedness of parents, offspring, siblings, and identical and fraternal twins.
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Video Transcript:
Hi, I’m Michael Corayer and this is Psych Exam Review.
In this video I’m going to provide a brief introduction to some of the ideas of genetics and the first idea is the idea that information can be passed from the parent to the offspring. This is what we mean when we say that something is heritable. We mean that it can be passed from the parent to the offspring through biological means.
So how is this information passed from the parent to the offspring? Well, it’s passed through genes. So what are genes? Well, a gene is just a way of talking about this information, it’s a unit. So a gene, we can say is a unit of hereditary information. So all this information is being passed from parent to the offspring and each individual piece of information is what we call a gene.
Now all of that information together all of the genes is referred to as the genome. OK so when we talk about the genomes of different species we’re talking about all the genes that get passed from the parent to the offspring. And when we compare species, we see that actually lot of these are similar. If we look at humans and chimps we see that their genomes are very similar. In fact they’re about 96% the same. So chimps and humans share about 96% of the same genes.
Now this might be surprising to you but if you think about what genes do it’s not so surprising. So you might ask, well what exactly do genes do? What genes do is they provide instructions. They tell that organism how to build that organism.
So a chimp’s genes tell it how to build a chimp and a human’s genes tell it how to build a human. So if you think of genes as instructions you realize that actually chimps and humans need very similar instructions because they have to build a lot of the same types of things.
We need to build blood vessels and hearts and skin, hair, and teeth and eyes and chimps need to build all of these things too. So they’re going to need a lot of the same instructions that we need and this is why our genomes are going to be so similar. We’re building most of the same types of things. They’re not identical but they’re very similar. Now you might ask, so this information gets passed from parents to offspring, but how do I get it from mom or from dad?
Well, when we talk about our genetic information, we talk about our DNA. So our DNA is essentially the set of all these instructions and it’s inside almost all of the cells in our body. The DNA is organized into chromosomes and humans have 23 pairs of chromosomes.
Each of these pairs, the way that it works is that you get half of the pair from your mom and the other half from your dad. This means that overall, amongst all these 23 pairs, half of your genetic information comes from your mom and the other half comes from your da. That means you’re going to share 50% of your genes.
So the way that it works is that a sperm cell will contain half of the sets of chromosomes, a half for each pair, and an egg cell will also contain half, then they get put together and that becomes you.
This allows you to be different from your siblings because they also get half the information but it’s a different half. The pair they get, they got this half from mom but you got that half of that pair from dad so it’s not the same information. This means that the same parents can create different offspring.
But on average they’re also going to share about 50% of their genes. So how does that work? Well, this is an average.
So if we’re talking about a particular gene you can either get the mom version of the gene or the dad version of the gene and your sibling, the same is true, they can either get the mom version or the dad version. So sometimes you both get the mom version, sometimes you both get the dad version. Sometimes you get the dad version, they get the mom version. Sometimes you get the mom version they get the dad version. So on average, for those four possible scenarios two of them are the same; you both get mom’s version or you both get dad’s version. So that is why we say you’re going to have 50% shared genes with your sibling. It’s not exactly 50% it could end up being slightly more or slightly less, but that’s an average.
Now, you might be confused at this point because you say “Mike you just said that we share 96% of our genes with chimps and now you’re telling me that I only share 50% of my genes with my brother”. Well we’re talking about different things here. When we talk about genomes, we talk about shared genes across species, we’re talking about the overall genome, the overall set of instructions. In that case if we talk about humans, humans have 99.9% shared genes.
You have pretty much the same genes as everyone else on Earth, any other human who has ever lived. You have pretty much the same genes, nearly identical. But when we talk about genes in families, now we’re talking about the specific types of individual genes. We’re saying you have the mom version of this version and your sibling has exactly that same version. Somebody else also has that gene but it might be slightly different. Or your sibling could have that same gene, but it’s the dad version. But the overall blueprint is the same.
So when we talk about shared genes in families we’re talking about specific individual genes, when we talk about shared genes across species, we’re talking about the overall structure of the genetic information.
OK so there is an exception with siblings. This is that some siblings share more than 50% of their genes. These are identical twins or if we want to sound more scientific we can call them monozygotic twins. This is just Greek for one zygote. So a zygote is a fertilized egg. It’s an egg and a sperm cell that have come together and what happens in monozygotic twins is that we have this single fertilized egg here, so one sperm cell, one egg, and then what happens is it splits and becomes two people. So this one egg splits into two and now you get two people but they have exactly the same information. They each got that same sperm cell, same egg cell. So this means they’re going to have 100% shared genes.
If we went through and looked when it comes to which version of the gene, do they have the mom version or the dad version for every gene it’s going to be the same. The other type of twins that we have are dizygotic twins. This is two zygotes. So what happens in dizygotic twins is that we have two separate eggs and two separate sperm cells that come in and fertilize each of those eggs so what happens is we end up with two people. But these two sperm cells have different genetic information these two eggs have different genetic information. So what happens is we end up just like any other siblings 50% shared genes.
So fraternal twins or dizygotic twins are sharing the same amount of genes as any other siblings, about 50% on average. In the next video I’ll talk about how we do studies of twins to try to determine how much we inherit certain traits or certain behaviors from our parents.
And we’ll see why it is that researchers are so interested in studying twins. Well hopefully this gave you a good understanding of some of the basic ideas of genetics, some of the terminology, so you know what genes are, genomes, DNA, chromosomes and we’ll go into more detail on many of these topics in future videos. I hope you found this helpful, if so please like the video and subscribe to the channel for more.
Thanks for watching!
