Evolution and Speciation Mechanisms of Evolution

Factors that affect Populations Genetic variation of individuals within a population makes evolution possible. Each new generation is made up of genetically unique individuals. Also, new mutations occur randomly new each generation These lead to creation of new alleles inherited from parents

Populations not individuals evolve Population:A localized group of individuals belonging to the same species. Species: A group of populations whose individuals have the potential to interbreed and produce viable offspring. Gene pool: The total collection of genes in a population at any one time.

Microevolution Changing percentages, or frequencies, of alleles within populations are the small events that lead to evolution within a population = microevolution

Hardy-Weinberg Principle The concept that the shuffling of genes that occur during sexual reproduction, by itself, cannot change the overall genetic makeup of a population.

Hardy-Weinberg Principle This principle will be maintained in nature only if all five of the following conditions are met: 1. Very large population 2. Isolation from other populations 3. No net mutations 4. Random mating 5. No natural selection

Hardy-Weinberg Principle Remember: If these conditions are met, the population is at equilibrium. This means “No Change” or “No Evolution”.

Microevolution The origin of taxonomic groups higher than the species level. A change in a population’s gene pool over a secession of generations. Evolutionary changes in species over relatively brief periods of geological time.

Factors that Cause Evolutionary Change Five Mechanisms of Microevolution Mutation Gene flow Non-random mating Genetic drift Natural selection

1. Mutation Mutation: Change in an organism’s DNA that creates a new allele. Randomly introduces new alleles into a population and can change allele frequencies in a population

2. Gene flow Net movement of alleles from one population to another due to the migration of individuals Occurs between two different interbreeding populations that have different allele frequencies Hamadryas baboons in Saudi Arabia. At some point in their lives, female Hamadryas baboons leave their birth group and migrate to a different one. This promotes gene flow between different groups, helping all populations maintain healthy and diverse gene pools.

3. Non-random mating Selection of mates other than by chance Individuals in a population select mates often based on their phenotypes Increases the population of particular characteristics Based on: Preferred Phenotypes Inbreeding

Preferred Phenotypes Choosing of mates based on their physical and behavioural traits Prevents individuals with particular phenotypes form breeding Only the individuals that mate will contribute to the gene pool of the next generation

Inbreeding Occurs when closely related individuals breed together E.g. self-fertilization of flowers Purebred animals tend to have a higher incidence of deformities and health problems compare with non-purebred animals. (lower fertility rates) E.g. Shar-pei dog -- hyaluronic acid and mucinosis

4. Genetic Drift The change in frequencies of alleles due to chance events in a breeding population. Sample size can greatly affect the gene pool of a population. The smaller the population, the less likely it is that the parent gene pool will be reflected in the next generation. In a large population there is a better chance that the parent gene pool will be reflected in future generations. Occurs by: Bottleneck Effect -Founder Effect

Bottleneck Effect Changes in gene distribution that result from a rapid decrease in population size Colonization of a new location by a small number of individuals, results in random change of the gene pool E.g. Darwin’s finches http://www.associatedcontent.com/video/492512/microevolution_by_genetic_drift.html?cat=7

BOTTLENECK EFFECT Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000 — but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted. Don’t kill me 

FOUNDER EFFECT Genetic drift resulting from the colonization of a new location by a small number of individuals. Results in random change of the gene pool. Example: 1. Islands (first Darwin finch) Darwin’s finches 18

FOUNDER EFFECT Founder effect A founder effect occurs when a new colony is started by a few members of the original population. This small population size means that the colony may have: a. reduced genetic variation from the original population. b. a non-random sample of the genes in the original population. Computer Simulation

FOUNDER EFFECT Example: Amish community Ellis-van Creveld syndrome, involves not only short stature but polydactyly (extra fingers or toes), abnormalities of the nails and teeth, and, in about half of individuals, a hole between the two upper chambers of the heart. The syndrome is common in the Amish because of the founder effect

5. Natural Selection The result of the environment selecting for individuals in a population with certain traits that make them better suited to survive and reproduce than other in the population Over many generations, frequencies of alleles of many different genes may change, resulting in significant changes in the characteristics of a population

MODES OF ACTION Natural selection has three modes of action: 1. Stabilizing selection 2. Directional selection 3. Diversifying selection Number of Individuals Size of individuals Small Large 22

1. STABILIZING SELECTION Acts upon extremes and favors the intermediate Reduces variation, improves the adaptation of the population to aspects of the environment that remain constant 23

2. DIRECTIONAL SELECTION Favors variants of one extreme Common during times of environmental change or during migration to a new habitat Peppered moths 24

3. DIVERSIFYING SELECTION Favors variants of opposite extremes Intermediate phenotypes can be eliminated 25

Animations http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf

Sexual Selection Natural selection for mating based, in general, on competition between males and choices made by females Combat Visual displays Sexual dimorphism