[Music] hi welcome back to three sighs lessons cold UK by the end of this video you should be able to describe what's meant by variation you should then be able to describe the causes of variation over the last few videos we've been looking at how genetics can control our inherited characteristics now one key idea in biology is variation variation is all the differences in the characteristics of individuals in a population in any population there are three main causes of variation the first cause of variation is the alleles that individuals have inherited these are genetic causes and we can see that with these people but examples of genetic variation or hair color and eye color red hair blond hair and dark hair are all genetic blue eyes and brown eyes are also genetic some variations caused by the environment for example the color of these flowers depends on the pH of the soil language in humans is another example of variation caused by the environment and finally some variation is caused by a combination of genes and the environment and a good example is height in humans some people have alleles which make them likely to grow taller however their diet must also include enough calcium for their bones to fully develop so in this case their final height is a combination of genetics and the environment now in any population of a species there's a massive amount of genetic variation and all of this genetic variation is due to mutations mutations are random changes to DNA mutations take place all the time and most mutations have no effect at all on the phenotype some mutations can influence the phenotype for example alleles for tallness may lead to tallness as a person's diet is suitable under small number mutations actually determine the phenotype a good example of this is eye color a key idea that you need to understand is that very rarely mutation can lead to a new phenotype sometimes the new phenotype can be beneficial if the environment changes and that can lead to a rapid change in the species I'm showing an example here in the 1950s a virus is going to the UK and until Dover 99% of wild rabbits however a mutation occurred which made the surviving rabbits resistant to the virus in other words this mutation give the rabbit a new phenotype now this beneficial phenotype is widespread in the UK rabbit population remember you find plenty of questions on variation in my revision workbook and you can get that by clicking on the link above [Music]