Okay. So now, let's talk about modern mapping. A lot of times, I get asked, you know, okay, this is great. I know how to do this with fruit flies, right? But is this actually real life? Do people answer is that they do sometimes. I'm sure people do, but that there are new types of gene loci maps. Now, the type you're familiar with, these are the recombination maps. Please use the recombination frequencies. These are the types that I explained to you. Now, there are physical maps, and this actually uses the genomic sequence. And how do you get this sequence? Well, you have to sequence the DNA, which is more advanced technology than they had during Morgan's time. And so, these are physical maps. You sequence the DNA, you have the nucleotides, and then you use those nucleotides to determine where the genes are located on the chromosome.
So you have to sequence the entire chromosome, or the genome of the organism to get the actual locations. Let me back up. And so, you can also map via certain genomic markers. These are also times where I use genomic sequencing. So, you can use single nucleotide polymorphisms. These are single nucleotide changes. And you can say, okay. Well, I know there are some SNPs here and there, or that's what you call them, SNPs. And say, I know that there are some SNPs here, some SNPs there. So let me use these SNP locations to determine where the gene is. You can use a restriction fragment length polymorphism (RFLPs), and these are DNA sequences that restriction enzymes cut. If you don't remember or have never heard of a restriction enzyme, all it is is a protein that cuts DNA at a specific sequence. So you can take the genomic DNA. You can cut it at specific sequences. You can then sequence that further to look at, you know, where the cuts were made, and how you can use that to determine gene locations.
And then you also have microsatellites, and these are short repetitive sequences found throughout the genome. There's a lot of repetitive DNA in our genome, and these are present in genes, and they're present in regulatory regions, they're present in, sort of, what's considered junk DNA or non-coding regions. They're present throughout the entire genome, and you use them to learn information about where genes are located. Genes with these sequences can be very easily identified through gene sequencing, because you just look for where the repeats are.
So, these modern mapping methods are much more commonly used today, depending on what you, kind of, need and what the scientists are looking for. But understanding traditional methods, they're super important to understanding the concepts of, like, how you identify where genes are on a chromosome, and recombinants, and parental types, and all the things that you learned. So, with that, let's unify.
