Hi, everyone. Today we are going to be talking about genetics. And, in particular, how our environment and our lifestyle, what we eat, and what we do, can affect our genetic makeup. Genes are units of inheritance, meaning they are sequences of DNA that code for proteins. Most of the DNA in our cells are coiled into chromosomes and stored in the nucleus of our cells. At the root of our DNA was have three major components, sugar, phosphate group and we have a base. The bases are broken down into four different types of bases, adenine, cytosine, guanine, and thymine for our DNA. And uracil for RNA. How DNA is coiled and condensed into chromosomes is going to dictate some information about what genes are expressed or turned on and which ones are not. Cells that carry DNA carry all of the DNA despite not using all of it to code for proteins. It is therefore important that the cell is able to pick different genes to express at different times. The amount of genetic information we have in our cells is pretty incredible. So there's over 3 trillion bases, which is about 20,000 genes. And actually, if we uncoil all of our genetic material from just one cell, it would be about six feet tall. So I already discussed that we have this compaction program that takes all of our genetic material and puts it into chromosomes. The chromosomes are going to be created by taking these long helical structures and then coiling them around groups of proteins called histones. So when we talk about chromosomes, we're really discussing a huge, long chain of nucleic acids that are going to be formed into a double helix. They're then going to be wrapped around histones. And that formation of genetic material, with the proteins of the histones, are called chromatin. And those chromatin are all packed and condensed and put into the nucleus of most of our cells. One of the really important things about genes and chromosomes is that all of the genetic information that our cells carry are all the same in all different cells regardless of what type of cell they are. What that means is we have a very elaborate packing routine and expression routine that allows some cells to behave, look, function and create proteins for their own cell, like a skin cell. And then something like a liver cell looks radically different and behaves radically different. So part of what we're going to examine today is how cells are able to express different protein and express different capabilities. The diploid number for humans is two sets of 23, which means the diploid number is 46 chromosomes for humans. And this is not true for all organisms. The number of chromosomes is not always indicative of a more evolved species, we just have very different types of DNA and chromosomes. This picture is depicting the the packing that goes into forming these chromosomes. So we take our helix, we form chromosomes, and then they're stored into the nucleus. So the picture that you're looking at is what's called the human karyotype. And it is a expression of all of the chromosomal components in any given cell and in all cells. And as I mentioned before, these chromosomal components, whether it's male or female, are going to be the same regardless of the cell that you take it from. Human karyotypes are really important because they're a great way to be able to identify any large-scale chromosomal abnormalities. So abnormal numbers, any breakages in the chromosomes, any translocations or any errors can actually be seen on these components. So at the root of genetics, we have this huge amount of DNA. And now what we have to do is we have to actually pick components and pick genes that we want to make into proteins. And again, the only reason that our cells look, act and behave differently is because different genes have been transcribed and then translated. So when we talk about DNA, the first thing that has to be done is it has to be transcribed into RNA. And then the RNA is able to then translate it into a protein for that cell. In addition DNA, is able to make more DNA, and this is something that is important for cell replication. We talked before in module one in cells' ability to replicate and be constantly creating new cells, which is why it's so important to be healthy and start to put effort into a healthy lifestyle. So in order to replicate cells at that level so that we have that new body next year, we're constantly going through DNA replication. And environmental, stress, and degradation can have an impact on if this is done well and without mutations or any errors. Sort of like typing on a typewriter and making sure you get all of the bases correct. So DNA replication is constantly going on in cells that are going to replicate, such as skin cells, and liver cells, and smooth muscle cells. But of course, things like neurons that we talked about don't actually replicate. In order for cells to divide, as I mentioned during mitosis or asexual reproduction, which is what the majority of cells are going to do, all of our somatic cells, skin cells, that I mentioned before, they're all going to be going through mitosis. And the importance for this is that this is the phase and this is the cycle where we're going to have DNA replication really be utilized because it's going to split into two new cells. So the importance here is that the health of these cells, as they go through mitosis, the speed at which they do it, the ability for them to make it through all these checkpoints without having mutations and errors, are going to create new healthy cells and tissue.
