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M.Ed., Stanford University
Winner of multiple teaching awards
Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.
Gametes are haploid cells that carry reproductive functions produced through meiosis. Gametes carried by males are called sperms and gametes carried by females are called eggs. By joining during fertilization, gametes form a zygote, which is a diploid.
Gametes are specialised haploid cells that are used to combine and when they do they combine to form a new diploid cell. That process of combination is called fertilization.
Now, you are hopefully familiar with sperm and egg, the two most common kinds of gametes that you've heard of. Where sperm they're small specialized for quick delivery of the DNA to the other cell, the other kind of gamete which is called the egg. Eggs are large. Why are they so large? It allows them to accumulate or store up large amounts of resources to provide for their newly developed diploid cell which will eventually become some new offspring like you and I became came from a single fertalized egg.
We take a look over here we can see in this scale, this thing that looks almost like a planet, that's the egg and you can see how much larger the egg is in size comparison to the sperm. Now if they were both the same size, they would be called isogametes.
We take a look at an isogamete. Every isogamete looks like the other. Now how are iso- how are sperm and egg made different? That happens during the process of either spermatogenesis or oogenesis.
Here we see a generic description of meiosis. The process of making gametes where here we have a cell that has let's suppose four chromosomes. Ultimately it can create four haploid cells. So this is a diploid cell. See it has pairs of homologous chromosomes. These are individual haploid cells, no more do they have those pairs of homologous chromosomes.
If this was spermatogenesis then all we'd have to do would be add in the specialization of tails etcetera and you've got yourself a sperm. With eggs however, in order to make that really large cytoplasm there's a large number of organisms such as human females who do a very specialised version of meiosis called oogenesis. Oo meaning egg. So with oogenesis, rather than having this one cell here during meiosis 1 do an equivalent cytokinesis so the two daughter cells here are of equal size. Instead one cell gets most of the DN- most of the cytoplasm, the other cell becomes this little thing called a polar body. Sometimes that little polar body just doesn't do anything. Sometimes it will go through its own version of meiosis 2 but still it just winds up being two little small things that were just somewhere to put the DNA that was not needed for the creation of the egg that's going to go on to form the human later on.
In the second division, again you have unequal cytokinesis so that one cell gets a lot of cytoplasm, the other one gets very little. That's it. That's gametes.
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