In this problem, we're going to learn about a practical application of biochemistry and also how studying the genomes of other animals can help us learn more about the human genome. A goal in biochemistry is to be able to treat inherited diseases. These are caused by defective genes or missing jeans. We can treat them by replacing the malfunctioning gene with a functioning version. But first we need to know what Jean does. What an example of a trait controlled by genes is size. There isn't much size variation in adult humans, making it difficult to study. However, there's an uncommonly large size variation for a single species in the domestic dog, ranging from tiny Chihuahuas, two giant Great Danes. It's almost hard to believe that this is a single species, despite the breed differences. Even in a single breed, there can be significant size variation, such as in the Portuguese water dog, which comes in both small in large sizes. Because there's also other morphological differences between breeds, it can be helpful to look at just size in a single breed. So what researchers did with sequence the DNA of a large group of Portuguese water dogs, they then identified the genes that were responsible for the difference in sizes. Next, they looked at an even larger population of dogs with multiple breeds both small and large, and confirmed that the genes responsible for the size differences and the Portuguese water dogs were also difference responsible for the differences in size and the other breeds of dog. These differences in DNA are called single nucleotide polymorphisms, or snips for short. Let's look a little more on the top in blue. We have the sequence for a small dog on the bottom. In green, we have the sequence for a large dog. You can see there's one pair that doesn't match up. This happens consistently among the small and large stock groups. We can identify a gene that's responsible for size differences now, Although researchers did find a single gene that largely seemed responsible for size differences inbreeds, there are also many other genes that affect size, which is why there's different sizes of German shepherds and different sizes of shit suits and different sizes of humans. However, you can see that by studying an animal with a large variation in sizes, it can help us to identify which genes are responsible for size, and then we can apply that understanding to humans and use it to help serve biomedical problems.