Genetic Variation

KEY CONCEPT A population shares a common gene pool.

Genetic variation in a population increases the chance that some individuals will survive. Genetic variation leads to phenotypic variation. Phenotypic variation is necessary for natural selection. Genetic variation is stored in a population’s gene pool. – made up of all alleles in a population – allele combinations form when organisms have offspring

Allele frequencies measure genetic variation. –measures how common allele is in population –can be calculated for each allele in gene pool

Genetic variation comes from several sources. Mutation is a random change in the DNA of a gene. Recombination forms new combinations of alleles. – can form new allele – can be passed on to offspring if in reproductive cells – usually occurs during meiosis – parents’ alleles arranged in new ways in gametes

Genetic variation comes from several sources. Hybridization is the crossing of two different species. – occurs when individuals can’t find mate of own species – topic of current scientific research

Genetic Variation Provide material for natural selection Brought about by mutation Provides genetic diversity – Allows a species to adapt a new niche in its environment Leads to natural selection

Phenotype

The observable characteristic of an organism such as coat color, eye color or size. Can be caused by genes, environmental factors, or a combination of both.

Phenotype Variation Is a fundamental prerequisite for evolution by natural selection. It is the living organism as a whole that contributes (or not) to the next generation, so natural selection affects the genetic structure of a population indirectly via the contribution of phenotypes. Without phenotypic variation, there would be no evolution by natural selection.evolution natural selection

Phenotype and Natural Selection Phenotypes provide an outward appearance for natural selections – Example: The peppered moth color variation was naturally selected according to the color of the forest that it lives within. – If the phenotype white is preferred in a light forest then the black moths find it hard to survive to reproduce thus leaving the white moths to reproduce.

Phenotype Variation Environmental factors are things in an organism's surroundings or lifestyle that can influence it in various ways. For example, body weight in humans may be influenced by genes, but is also influenced by diet. In this case, diet is an example of an environmental factor

Phenotype Variation A lot more is known about the relationship between genes and phenotypes. Let's take the example of hair color. Perhaps there is a gene in rabbits that codes for an enzyme that, in turn, makes a brown-colored pigment in hair follicles. Some rabbits may have genetic differences that cause them to have more or less of this enzyme, or enzyme that works more or less efficiently to produce the pigment. We would expect these rabbits to have different phenotypes, e.g. lighter or darker brown hair, depending on these genetic differences.