Evolution Biology Review
Charles Darwin • Known as the Father of Evolution • Wrote book On the Origin of Species • Sailed the world on a ship called the Beagle
Evidence for Evolution • The fossil record – show biodiversity, mass extinctions and episodic speciation • Geographic Distribution of Living Species – shows similarities among species living on different continents • Homologous Body Structures – structures that have different mature forms but come from the same embryonic tissue. • Similarities in Early Development – embryos of many vertebrates are very similar.
What are Populations and Gene Pools? http://www.copernicusproject.ucr.edu/ssi/HighSchoolBioResources/Evolution/Fossils_and_the_Study_of_Evolution.asf
Natural Selection • Over time natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness (ability to survive and reproduce) in its environment. • Natural Selection causes struggles for existence and survival of the fittest. • Natural Selection act on the phenotype rather than the genotype of a species.
Gene Pools • A gene pool is the combined genetic information of all the members of a particular population. • A gene pool typically has two or more alleles for a given trait. • Homozygous lethal traits can be carried by heterozygous individuals and thus remain in a gene pool. • Relative Frequency is the number of times an allele occurs in a gene pool compared with the number of times other alleles occur.
What are gene pools? http://www.copernicusproject.ucr.edu/ssi/HighSchoolBioResources/Evolution/What_are_Populations_and_Gene_Pools_.asf
Sources of Variation • Two main sources are mutations and gene shuffling. • Mutations – changes in DNA sequence. These may or may not affect an organisms fitness. • Gene shuffling – is the random shuffling of genes caused by sexual reproduction.
Natural Selection on Single-Gene Traits • Natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution. • If the change is beneficial to the organism, the change may cause the original form to fade out and the newer organisms to be more fit and take over.
Natural Selection on Polygenic Traits • Natural Selection can affect the distribution of phenotypes in a population in any of three ways: directional, disruptive and stabilizing.
Directional Selection • Directional Selection – Evolution causes an increase in the number of individuals with the trait at one end of the curve.
Stabilizing Selection • Individuals in the center of the curve and more fit and thus the curve narrows
Disruptive Selection • Individuals at the ends of the curve are more fit than the ones in the middle causing two curves to form and possible new species to form.
Genetic Drift • In small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population.
Hardy-Weinberg • Genetic equilibrium takes place when allele frequencies remain constant. • In order for genetic equilibrium to take place, five factors must remain true. • 1. random mating • 2. Large Population • 3. No movement in or out of the population • 4. No Mutations • 5. No Natural Selection
H-W Conditions http://www.copernicusproject.ucr.edu/ssi/HighSchoolBioResources/Evolution/Introduction___The_Hardy___Weinberg_Principle.asf
Speciation • Reproductive Isolation occurs when members of two populations cannot interbreed. At that point, they have different gene pools.
Types of Isolation • Behavioral Isolation – Two populations capable of interbreeding but have differences in courtship rituals or other types of behavior. • Geographic Isolation – Populations are separated by geographic barriers such as rivers, mountains, or bodies of water. • Temporal Isolation – Species reproduce at different times of the year.
Galapagos Finches • Speciation in the Galapagos Finches occurred by founding of new populations, geographic isolation, gene pool changes, reproductive isolation, and ecological competition.
Survival • Variation within a species help insure that some will survive major changes in the environment. • Major diversity of species also insure that some of the species will survive major environmental changes.