Okay. So we talked about DNA, let's now talk about chromosomes. Chromosomes come in different types of formations. The one you're going to hear about a lot are homologous chromosomes. These are just pairs. You have 2 chromosomes that are homologous because they are paired together. Now, diploid, another term you're going to hear, is represented as 2n. These are organisms that have homologous chromosomes, meaning they have a chromosome pair. Then, you have haploid, which has one less chromosome. So instead of having a pair, it just has one chromosome copy. Diploid is sometimes written as 2n because of the two chromosomes, and haploid is written as n because of the one chromosome.
Chromosomes are so important for genetics and inheritance because the chromosomal theory of inheritance states that traits come from genes on chromosomes. Without chromosomes, you're not going to inherit anything. The genes sit on the chromosomes, and you inherit the chromosomes that are on those genes. The chromosomes that are inherited are passed through what's known as gametes, which are sex cells. So these are sperm and eggs if we're talking about humans.
Now, how do we get gametes? This is through the process called meiosis. This process produces gametes. In diploid individuals, like humans, you take a 2n cell, a diploid cell. Over time, through a series of steps which we'll discuss in great detail, you end up with four haploid cells. These haploid cells then go on to fuse or combine with other haploid cells to create a diploid organism. In our case, these haploid cells are sperm and eggs. When they come together, they create a diploid zygote. Don't worry if you don't get all of that down now. Hopefully, this is a review, but if not, we're going to talk about this in a lot more detail in the future.
Then there's mitosis, which we're not going to talk about a lot in this class. We're mainly going to focus on meiosis, but mitosis does still exist. We'll talk about it briefly. Mitosis is the process of creating somatic cells. Somatic cells are every cell that is not a gamete. So, they include your skin cells, eye cells, brain cells, toe cells, literally all the cells that aren't sperm and eggs in humans. This process takes diploid cells and turns 2n cells into more 2n cells. So with meiosis and chromosomes, what you get is you start with a diploid organism, it undergoes meiosis, and you end up with haploid cells, so one copy of each chromosome. These are the homologous chromosomes. You end up with one copy after meiosis in each cell. Then, through fertilization, the combining of the sperm and egg, that will create another diploid organism.
Like I said, we'll go over these in a lot of detail. These are just basic review fundamentals. So now, let's turn the page.
