Hi and welcome back to freesciencelessons.co.uk. By the end of this video you should be able to describe the differences between sexual and asexual reproduction. In a previous topic we saw that human cells contain 23 pairs of chromosomes in the nucleus and I'm showing you a human cell here. Now you'll notice that this diagram only shows four pairs of chromosomes. That's to make the diagram easier to see.
But you need to remember that human cells actually contain 23 pairs of chromosomes. We saw that cells can divide by mitosis. In mitosis, one cell is copied into two identical cells.
And I'm showing you that here. Now there's one type of cell where the chromosomes are not paired. These cells are called gametes. And in humans, the gametes are sperm cells and egg cells.
I'm showing you human gametes here and I should point out that this diagram is not to scale. Sperm cells are actually much smaller than egg cells. You'll notice that in gametes the chromosomes are single, not paired.
So human sperm and egg cells both contain 23 single chromosomes. But again remember that this diagram only shows four chromosomes. Now a key fact that you need to learn is that gametes are made by a type of cell division called meiosis. We'll be looking at meiosis in more detail in the next video.
Unlike mitosis, meiosis produces non-identical cells. In other words, every sperm cell and every egg cell are different. Meiosis also takes place in flowering plants.
In this case the gametes are pollen and egg cells. Both animals and flowering plants carry out sexual reproduction, so we're going to look at the features of sexual reproduction now. The first key point that you need to understand is that sexual reproduction involves the fusion of male and female gametes.
And the word fusion means joining. Scientists call this process fertilisation. So this shows a sperm cell joining with an egg cell. Now what that means is that in sexual reproduction there is mixing of genetic information.
In other words the offspring receives genetic information from both the male and female parents. Now as we said before every gamete's different. So this means that we can see variation in the offspring. And we can see that with these puppies.
Okay, I'm showing you here an aphid reproducing, and this is an example of asexual reproduction. So we're going to look at that now. In asexual reproduction, there's only one parent. So this aphid is the only parent of the offspring.
This means that asexual reproduction does not involve gametes. Because there's only one parent, there is no mixing of genetic information. And the offspring are all genetically identical. Scientists call these offspring clones. Now because asexual reproduction does not involve gametes, meiosis does not take place.
Asexual reproduction only involves mitosis. I'm showing you another example of asexual reproduction here. This plant reproduces by forming these tiny buds.
The buds drop off and grow into new plants. The offspring plants are genetically identical to the parent. In other words they're clones.
Remember you'll find plenty of questions on sexual and asexual reproduction in my vision workbook, and you can get that by clicking on the link above.