in today's video we're going to take a look at selective breeding which is basically where you take the best plants or animals that you have in your population and then you breed them together in the hope of getting even better offspring next time now this idea isn't anything new humans have been using selective breeding for thousands of years ever since we first started agriculture which is just a fancy term for farming now though we use it all the time and we selectively breed for all sorts of things like for cows that produce loads of meats or milk for crops that are resistant to diseases for friendly cats and dogs that make us lovely pets and for plants that have large or unusual flowers so how does it actually work well first you take a look at the individuals in your existing stock so that might be all of the different tomato plants in your field and you select the ones that have the characteristics you're after for example these two with lots of big tomatoes and then we can breed these ones together to give us the next generation which will hopefully contain some even better plants we don't just do this once though we do it over and over again always picking the best ones from each generation and breeding those ones together to get a better generation next time to see just how much things can change take a look at this picture which shows the original form of sweet corn that we first found in the wild over ten thousand years ago and compare it to this modern type you can see this sort of change in all different plants and it's just a result of repeated selective breeding as we try to get better bigger and more juicy plants as always though there are some drawbacks and the main one is that selective breeding reduces the gene pool of the population and if you haven't heard of the term gene pool before it's basically the collection of all the different alleles held by an entire population whenever we do selective breeding what we're actually doing is selecting for certain alleles that code for the traits that we want so as we do this over and over again we're going to get a smaller and smaller pool of alleles as we get rid of all the bad ones and only keep the good ones and because the best individuals are often closely related because they both have the good genes breeding them together can sometimes lead to inbreeding which makes the offspring particularly prone to diseases and inherited defects because their gene pool is so small this is the reason that dogs like german shepherds and rottweilers are so prone to health conditions a small gene pool also means there's less variation within the population so if we were to go back to our tomato plants and imagine that a new pathogen arrived which infected one of the plants then chances are it could probably affect all of them so the farmer might lose his entire crop at once and that's all for today so if you enjoyed it then please do give us a like and subscribe and we'll see you next time