 All right, dog pounds, let's look at the concept of penetrance. Are you ready? Penetrance is this idea that not everyone who has a specific genotype is going to express the phenotype. All right, let's go back to pea plants just for an easy, accurate example. In pea plants, if you have a homozygous dominant, what's the word? Genotype, then you're going to make purple flowers. If this happens 100% of the time, then the penetrance equals 100%. If, really? I mean, my understanding is that this happens 100% of the time, not so. Sometimes, for example, with a condition called retinoblastoma, I can do this, retinoblastoma, okay, I've got a picture of it, I'll show you the picture. This is a condition where it's genetic and it has something on your retina, this little fellow's retina and it's got whatever those things are on the retina. If it is a genetic condition, so if you have the genotype and 75% of the people who have the genotype to get this phenotype, get the phenotype, then it's 75% penetrance. And if 90% of the people who have the phenotype have the genotype, get the phenotype or express the phenotype, then it's 90% penetrance. With a form of dwarfism called achondroplasia, that's a genetic condition, and that's 100% penetrance. So if you have those alleles, then you will display the phenotype that you would expect. For me, I started thinking about that and I'm like, dude, how can you ever draw any conclusions? Because you would never know is the variety that I'm seeing because there are multiple genes involved or is the variety that I'm seeing because there isn't full penetrance in this particular situation. And then of course I have to be like, why? Like, is there something about the people where it's not penetrating that is unique? Like, I find this one really fascinating. This is an excellent example of how it's so much more complicated than we even know. And this next one is hopefully going to hit it home for us all that, wow, we're complicated critters. I'll be right back.