MICROEVOLUTION Mechanisms of

POPULATIONS Populations are groups of individuals that can breed with one another and are localized in certain regions. Some populations are isolated from others. Still others can easily mix with other members of a population.

POPULATIONS Within a population, all of the genes are called the gene pool and it consists of all alleles at a given locus. If only one allele exists in a population, it is said to be fixed and all individuals are homozygous. If more than one allele exists, then individuals are either homozygous or heterozygous.

Remember Genetics? Let’s recap Allele Frequency & Hardy-Weinberg

Allele Frequency Consider a population of 500 with 2 alleles, C R and C W C R C R gives Red C W C W gives White C R C W gives Pink

Allele Frequency Our Population Breakdown: 320 red, C R C R 160 Pink, C R C W 20 White, C W C W There are still only 2 alleles within our population for this trait

5 Conditions that result in Evolution: 1. Small population size 2. Non-Random mating 3. Mutations 4. Natural selection 5. Gene Flow These 5 conditions results EVOLUTION in EVOLUTION, more specifically MICROEVOLUTION

Mutation and Sexual Recombination These provide variety within gene pools. Mutations are changes in the nucleotide sequences that give rise to new genes and new alleles. – Sometimes they’re good, usually they are not. Most mutations occur in somatic cells and are never passed on. – Only a small percentage of gametes ever get into the populations, so any mutation occurring in the gametes likely won’t get passed on.

Mutation and Sexual Recombination Mutation rates in general are low. The larger the organism the less likely a mutation will occur and vice-versa. – For example: Plants and animals with long generation times are relatively large and have a much lower frequency of mutations than do microorganism and viruses.

Mutation and Sexual Recombination Sexual recombination is the best way to produce variation within a population on a generation-to-generation time scale.

Evolution is a change in allele frequency brought on by mutation and sexual recombination Evolution is a change in allele frequency brought on by mutation and sexual recombination There are 3 factors which cause the most evolutionary change by altering allele frequencies 1. Natural selection 2. Genetic drift 3. Gene flow

Organisms More Fit to Survive Organisms Pass on these Traits Change in Allele Frequency within a Population 1. Natural Selection As you know, when organisms are more fit to survive, they are more likely to pass on the traits that make them better suited for survival and this often changes the allele frequency within a population. Mutation Occurs in Organism(s)

2. Genetic Drift Genetic drift is an unexpected fluctuation in allele frequency from one generation to the next. This is often due to a chance event where a large proportion of the population is wiped out.

2. Genetic Drift There are two situations which increase the likelihood of genetic drift that have a large impact on a population: A. The bottle neck effect B. The founder effect

A. The Bottle Neck Effect A sudden change in the environment which drastically changes a population can have a profound impact on the genetic makeup of the population. It may change the population in such a way that the survivors no longer represent the original population. The survivors are said to have gone through a “bottleneck.”

The Bottle Neck Effect

B. The Founder Effect Occurs when a few organisms become isolated from a large population and establish a new population whose gene pool is not reflective of the large population. These founders pass through an isolation bottleneck and represent a gene pool with altered allele frequencies.

3. Gene Flow Gene flow occurs when populations gain or lose alleles as organisms come and go within a population Gene flow tends to reduce differences between populations. Also known as Migration