VARIATION

=Variation= Variation in the features (phenotypes) of individuals within a population is the result of both genetic and environmental influences. Some complex traits such as intelligence are a combination of the two. Hundreds of genes have been linked with higher intelligence, but environmental influences such as a person's nutrition and experiences (learning) clearly play an important role too. ==Non-Heritable Variation== [image:http://i.imgur.com/rVx5L7h.png?2] Non-heritable variation is responsible for any '''acquired''' differences in the phenotypes of individuals in a population. These differences are usually the result of environmental influences or the actions of individuals. For instance the ability to play the piano is an acquired trait as this has to be learnt. A scar or tattoo is another example of an acquired trait. ==Genetic (Heritable) Variation== [image:http://i.imgur.com/QPB4Ley.png] Even between members of the same species there are subtle differences in their DNA sequences. Different people often carry slightly different forms of each gene called alleles. '''The number of different alleles''' (or allele combinations) within a population are referred to as Genetic Variation. Genetic variation produces a wide range of different phenotypes (characteristics) within a population. '''Mutations''' are ultimately the source of genetic variation as changes to the base sequence of a gene are what generate new alleles (versions of a gene). When a mutation occurs in a gene its sequence is altered and it may encode a new phenotype (characteristic) Sexual reproduction generates greater genetic diversity. This is because the following processes generate unique combinations of alleles during meiosis. This produces offspring with unique combinations of alleles and therefore usually some unique phenotypes. *'''Segregation''' *'''Independent Assortment''' *'''Recombination''' (crossing over) =Advantage of Variation= The advantage of having variation within a population is that some individuals will be better adapted to their environment than others. Those individuals who are not well adapted to their environment are less likely to survive and reproduce. Those individuals that are best adapted are more likely to survive and reproduce, passing on their favourable traits (adaptations) to their offspring. This process is is known as '''natural selection''' (sometimes referred to a "survival of the fittest") and is what drives evolution. [image:http://i.imgur.com/IXRaxfY.png?1] This is particularly important when environmental conditions change. If there is little variation within the population it may die out (extinction). If there is sufficient variation, some individuals will have adaptations that enable them to survive and reproduce, ensuring the survival of the species. Environmental changes could include: *Changes in '''climate''' *The introduction of a new '''predator''' *Changes in '''prey''' / availability of different '''food sources''' *Disease (the emergence of a new disease or strain) [image:http://i.imgur.com/gPp5CaC.gif?1] '''Some Key Ideas!''' *Evolution does not occur within a single generation. No individuals can "adapt" to their environment. *Only large groups (populations) can evolve adaptations over long periods of time (many generations). *No one can chose or try to adapt. It's purely up to chance whether or not an individual has inherited a combination of adaptations that will help them survive and reproduce.