Genetic Variation and Evolution

Genetic Variation and Evolution

• Evolution refers to changes in a species over time.
• Darwin's Theory of Evolution emphasizes variation within populations, leading to adaptation.
• Individuals in a population exhibit varying traits which can result in adaptation and the evolution of species.
• Overproduction occurs as populations tend to produce more offspring than can survive, which leads to resource scarcity and competition.
• Competition leads to a struggle for existence, where more successful individuals survive and reproduce.
• Survival of the fittest describes how organisms best suited to survive and reproduce will leave more offspring.
• Adaptation involves organisms exhibiting heritable changes for survival in a changing environment.

Sources of Genetic Variation

• Mutation and meiosis provide variation within a species.
• Point mutations include substitutions and deletions.
• Chromosomal mutations include translocations and inversions.
• Meiosis involves crossing over, independent assortment of alleles, recombination, nondisjunction, and polyploidy.

History of Evolutionary Thought

• Charles Lyell(1830s) studied geologic history and fossils and determined that different organisms lived at different times.
• Thomas Malthus (1798) stated that populations grow infinitely, but certain factors prevent it.
• Jean Baptiste Lamarck (1809) introduced the concept of "Use and Disuse," stating Characteristics are inherited and passed to next of kin, but was incorrect in his use and disuse theory of acquired traits.
• August Weismann disproved Lamarck by cutting tails off mice, proving acquired traits are not inheritable.
• Charles Darwin (1859) Published book 20 years after the Galapagos and Alfred Wallace developed same ideas in 1858, presenting his work together in 1859, with Darwin publishing "The Origin of Species by Means of Natural Selection".

Agents of Evolutionary Change

• Mutation is an agent of evolutionary change.
• Gene flow is an agent of evolutionary change where new alleles enter/exit a population.
• Non-random mating is an agent of evolutionary change where mates are picked based on selective criteria
• Natural selection and selective breeding are agents of evolutionary change, where certain alleles increase survival chances.
• Genetic drift is a random change in allele frequencies, especially in small populations, and has two forms: founder effect and population bottleneck.
• The founder effect happens when a small group founds a population with little diversity and all future generations exhibit little variation.
• The population bottleneck happens when a population is drastically reduced in size, leading to very little genotypes surviving from the original population which results in decreased genetic diversity.

Measuring Evolutionary Change

• Changes in allele frequencies based on observed phenotypes can determine how a population changes.
• Allele frequency refers to the percentage of the population expressing a particular trait.
• Population change happens if allele frequencies change.
• The Hardy-Weinberg Principle says that allele frequencies can be mathematically determined.
• Allele frequencies remain unchanged if there is no mutation, no selection, no gene flow where the population is isolated, there is a large population, and that random mating occurs.
• Hardy-Weinberg Equation: p² + 2pq + q² = 1.00

Fitness and Natural Selection

• Evolutionary fitness is determined by the number of offspring that survive to the next generation.
• Natural selection places pressure on organisms to survive.
• Members of a species with the best adaptations (alleles) survive and reproduce.
• Environmental changes (selective factors) determine which alleles are most fit for survival such as disease, predation, resource gathering, changes in weather, new species occupying a niche, food type/availability.

Types of Natural Selection

• Stabilizing Selection favors heterozygous genotypes.
• Homozygous genotypes are selected against during Stabilizing Selection.
• Hybrid vigor and heterozygous advantage are components of stabilizing selection.
• Directional Selection favors one homozygous genotype over others, which often occurs with recessive or dominant genetic diseases.
• Disruptive Selection selects against the intermediate (hybrid) phenotype.
• During Disruptive Selection Homozygous genotypes are selected for survival.

Evidence of Natural Selection

• Darwin's Finches show how beak size and type are selected by food supply which also highlights how the best-adapted individuals survive changes in food type.
• Peppered Moths provides evidence where the dark form of moth is favored in areas of high pollution because darker color provides protection from predators, conversely, in less polluted areas the selective advantage is held by the lighter form.
• Industrial melanism happens when industry affects the frequency of the melanic (dark) phenotype.

Evidence of Evolution - Other concepts

• Artificial Selection happens when humans select traits over a short period of time.
• Comparative Biochemistry demonstrates similar DNA codes and proteins with common ancestry.
• Comparative Embryology happens as embryos possess similar structures during development.
• Behavioral Biology demonstrates that threat responses are similar in animals.
• Fossils indicates bone structure and size, determines age, and other factors such as habitat, food, method of reproduction, predators, prey.
• Homologous structures have a similar structures with possibly different functions.
• Vestigial Structures are structures that have no current function but are similar to functional structures in other species.
• Analogous structures are similar adaptations in unrelated species functionally similar and structurally different like blubber in arctic animals and fin structure with bony fish and sharks.

Biogeography and Evolution

• Observations of species' movements and locations compared to fossils can show Evolution.
• Adaptive radiation happens when ancestral species migrate to new locations in response to selective pressures where new species may result if enough different alleles are selected.
• Endemic Species are unique organisms found in one location that specialize in a specific niche, such as Kangaroos, koalas, giant tortoises, and the quokka.

Phylogenetic Trees

• Phylogenetic trees (cladograms) graphically represent the evolutionary relationships between species.

Species and Speciation

• A species is an interbreeding population that is reproductively isolated from other groups and produces fertile offspring.
• Reproductive isolation happens when one population cannot produce fertile offspring with another.
• Prezygotic reproductive isolation happens before zygote formation by geographic isolation, temporal isolation, behavioral isolation, ecological isolation, mechanical isolation, or prevention of gamete fusion.
• Postzygotic reproductive isolation happens after a zygote forms as Zygote inviability happens, an infertile hybrid forms, or an inviable hybrid forms.
• Allopatric Speciation (Adaptive Radiation) happens when a population is split and adapts to new environments.
• Divergent Evolution occurs when a species is split during Allopatric Speciation.
• Sympatric Speciation (Same Location) happens when a new species emerges within one population with chromosome number changes and disruptive selection of alleles which is common in antibiotic resistance in bacteria.
• Gradualism describes evolution occuring slowly.
• Punctuated Equilibrium (1972) states that species experience long periods of no change, punctuated by short periods of rapid change.

Adaptations for Survival

• Defensive mechanisms in plants and animals help them survive by using toxins, tannins, or physical structures and camouflage.
• Aposematic Coloration is a warning color exhibited by toxic/stinging organisms with bright and specific patterns.
• Camouflage conceals the body using countershading (dark dorsal surface and light ventral surface) or cryptic coloration (blends color pattern matches background)or disruptive coloration (Confuses predators and prey).
• Mimicry happens as species copy color patterns for protection like Batesian when a mimic can be non poisonous, or Mullerian is when several species with the same toxin or sting share similar color patterns.