Homologous Chromosomes

in this video, we're going to begin our introduction to homologous chromosomes now, before we define homologous chromosomes, its first helpful to point out that a carry a type is defined as an order display of all of the chromosomes in a cell. And so, if we take a look at our image down below, over here on the left hand side, notice that we're showing you a human Correa type, and you can see that it's an order display of all of the chromosomes and one single cell. Now it's important to note that human somatic cells or human body cells contain 23 pairs of chromosomes. Now, within each pair of chromosome, there are actually two chromosomes, just like within every pair of shoes. There are actually two shoes, and so there are 23 pairs of chromosomes, but that's actually a total of 46 chromosomes Now. This is really important because sometimes your textbooks in your professors will use 23 pairs of chromosomes and other times they'll use a total of 46 chromosomes to define the total number of chromosomes and human somatic cells. Now, of these 23 pairs of chromosomes found in human somatic cells. 22 of those 23 pairs are known as autos. OEMs and autism's is really just the fancy scientific name for non sex chromosomes or chromosomes that air not related to the sex of the organism, whether the organism is male or female, and so these 22 pairs of autism's because they are non sex chromosomes, they're going to be found in both males and females. Now, of course, if 22 pairs out of the 23 total pairs are autism's, then that only leaves one pair left. And so the one pair that's left is going to be, uh, include the X and Y chromosomes, which are going to be sex chromosomes. And, of course, sex. Chromosomes, as their name implies, are going to determine the sex of the organism, whether the organism is female or male. Now, females, which are symbolized with this symbol here, which is basically a circle with a plus sign right below it. Females contained two X chromosomes, whereas males, on the other hand, whose symbol looks like this basically a circle with a narrow coming off of it are going to only have one X chromosome and a Y chromosome instead of an X chromosome. And so, if we take a look at our image down below at this human carry, a type notice that we can see these pairs of chromosomes and these pairs of chromosomes notice have numbers below them to keep track of them and noticed that we're showing you with a green background, that there are 22 pairs of chromosomes that air known as autism's. And so here with greenish background, were saying that there are 22 pairs of autism's or non sex chromosomes, and those down below here in pink were saying that that 23rd pair is going to be the sex chromosomes. So there's one pair of sex chromosomes. And of course, uh, it could either be X X if it's a female or it could be X Y if it's a male and so you could see the X X here if it's a female or it could be X Y if it's a male. Now, each of these pairs of chromosomes that we see here are really defined as homologous chromosomes, and so homologous chromosomes are going to be pairs of chromosomes that are very, very similar in size, shape and carry the same genes, but can have different versions of those genes or different Ah Leal's. And so it's important to note that homologous chromosomes are going to be very similar, but they're not necessarily going to be identical to each other. And so again, they're going to be similar in size and shape, and they're going to carry the same sets of genes. But again, they can have different versions of those genes or different a Leal's. Now. Also, what's important to note is that within each homologous chromosome pair, one of those, uh, chromosome is going to be paternal E inherited or inherited from the father's sperm, and the other chromosome is going to be maternally inherited or inherited from the mother's egg. And so if we take a look at our image down below again, all of these pairs that we see here would represent homologous chromosomes because once again they are similar in size and shape. They carried the same genes but can have different Khalil's. And so if we were to zoom into just one of these pairs of homologous chromosomes, as we're doing over here in this box, zooming into this one pair of homologous chromosome over here again. This would be an example of homologous chromosomes and homologous chromosomes, which will notice is that they are similar in size and shape. And so notice here that we have, uh this chromosome over here on the left hand side is very similar in size and shape to this other chromosome over here. And so the blue and the pink chromosomes are homologous chromosomes. And so what you'll notice is that some of the genes on these homologous chromosomes might be identical to each other, such as this. Gene A is identical in both homologous chromosomes. However, other genes may not be identical. And so notice that the blue chromosome over here is going to have the Capital B version of the gene or the capital B alil, whereas this pink one over here is gonna have lower case B version of the gene or lower case B. Alil. And so these here are representing thes a Leal's and sometimes again thes. Jalil's can be identical between homologous chromosomes, but other times Thea Leo's will be non identical between the homologous chromosomes. Now here, as we're showing you the chromosomes these air replicated chromosomes with Sister Crowe mated. So over here, this represents one sister Crowe matted. This represents the other sister Crowe matted and the sister Chromatic. They're called Sister Chromatis because these are identical to each other. Uh, and notice Over here. This chromosome also has a sister chromatic IDs that are identical to each other. But notice that the sister chromatic of homologous chromosomes do not necessarily have to be identical to each other. So this chrome, it'd and this chrome it'd of the other homologous chromosome. They are identical at this, a position, but they are none identical at the B position because this one has a capital B, and this one has a lower case B. And so it's important to note that homologous chromosomes are not necessarily going to be identical to each other, and in fact, in most cases they will not be identical to each other. And so this here concludes our introduction to homologous chromosomes, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video