Welcome back to our course on Introduction to Cancer Biology. My name is Dr. Amend, and today we're going to be talking about the genetics of cancer. By the end of this session, you'll be able to describe the contribution of genes to the risk and growth of cancer. You'll be able to describe what a gene is, distinguish between inherited and somatic mutation, and compare and contrast oncogenes and tumor suppressors. You'll be able to use all of this information to then describe how cancer is a genetic disease. To start off with, we'll just be going through a basic introduction to genetics. Cancer is a genetic disease and it's caused by an accumulation of detrimental variation to the genome. It's important to member that a single mutation is not sufficient to induce cancer formation. But before we can start to understand how cancer is a genetic disease, we need to first understand what a gene is. So a gene was first described by Gregor Mendel. He was an Austrian monk, and he's known as the father of genetics. He studied pea plants, he studied their shape, their color and their height, and first published his findings in 1866. So this idea of genes and genetics is certainly not a new one. He described that a gene is a discrete unit of heredity of a living organism. In molecular biology, we describe gene as a region of DNA that encodes for a functional product. What we mean by a functional product is RNA or protein. Humans have about 25,000 genes in the genome, and the genome just describes all of the genes of an organism. So let's unpack this a little bit. What is DNA? DNA stands for deoxyribonucleic acid, and it's present in the nucleus of most cells in the body. DNA provides instructions for all processes of the body, and is made up of bases that bind to each other to form a twisted ladder, which is known as the double helix. What you can see in the cartoon on your left is an ideogram of what this twisted ladder looks like. Pyrimidine, the T, is binding to Adenine, A, and the C, Cytosine, is binding to Guanine, G. And again, these four bases represent the bases that make up DNA. Every time a cell divides, it must replicate its DNA in order to pass on the instructions for life to its daughter cells. In a single nucleus of a cell, 5 to 6 feet of DNA is contained. So how can so much DNA be packed in such a small area without getting tangled and broken during replication? Organisms have solved this problem by packing DNA into chromosomes, which you can see in the fluorescence in situ hybridization or fish, that is on the right. What you see on the right are chromosomes 1 through 22 of humans, plus the sex chromosomes, in this case, two Xs. You'll notice that there are two for every chromosome number. This is because humans are diploid, they have two copies of every gene. There is one maternal and one paternal. And all of the genes of an organism contained in these chromosomes make up the genome. So then how does the information from DNA that makes up a gene become an observable trait? That observable trait we call a phenotype. This is explained by what is known as the central dogma of molecular biology. It usually goes that DNA goes to RNA goes to protein. So let's unpack that a little bit. Every time a cell divides, it replicate its DNA and makes a copy of its DNA to then give to its daughter cells. This DNA stays in the nucleus except during cell division in order to protect it. That way we don't have more and more errors arise in the DNA over time. The RNA is the code of DNA genes, so it's transcribed or copied from the DNA. So this is then exported from the nucleus into the cytoplasm. This code, this copy of the code, the RNA, is then translated into protein, and proteins are what does the work of the cell. So proteins make up the structure of the cell, they're important for signal transduction for communication and metabolism in the cell. So then how do different types of cells do different things? Why isn't an eye cell a liver cell? Remember every single cell in the body contains the same type of DNA. The way an eye cell and a liver cell are different, are because even though every cell has the same DNA, only a subset of genes are then transcribed into RNA, and this is described in the field of epigenetics. So we can make an analogy then between genetics, genes, and epigenetics when we think about traffic patterns. On the image to your left, you see cars driving on a road with traffic lights. In this case, the road describes the DNA genes, it's the same for everybody. The traffic pattern, or where the cars are actually going on the road, describes gene expression. The traffic lights regulate which cars get to drive where. It regulates which genes are transcribed into RNA in every cell, and this is known as epigenetic regulation. So this is a good time to take a break. And when we come back, we'll talk about genetic variation and mutation.