3 Darwin in a nutshellIndividual organisms in nature differ from one another.Organisms in nature produce more offspring than can survive.Because more organisms are produced than can survive, competition for limited resources takes place.Since each organism is unique, each has distinct advantages and disadvantages in the struggle for existence.
4 Darwin (con’t)Individuals best suited to their environment survive and reproduce most successfully. The characteristics that make them survive are passed on to their offspring.Species change over time.Species alive today have descended with modifications from species that used to live in the past.All organisms on Earth are united into a single tree of life by common ancestors.
5 Gene PoolsA gene pool is the combined genetic information of all the members of a particular population.
6 Sources of Genetic Variation Mutations –A change in sequence of DNA. Things that can cause mutations:Mistakes in DNARadiationChemicalsThey can affect a single base, a length of DNA or an entire chromosome
7 Genetic Shuffling –This is basically the genetic variation that occurs with the process of sexual reproduction (crossing over, 4n, etc.)
8 Genetic DriftOccurs when one portion of the population finds a new habitat.Now, there are different types of genes present in the new gene poolThis creates a new population.
9 Genetic EquilibriumThis is a situation where allele frequencies (the amount of times a trait occurs) stay the same.In order for this to happen, the following must occur:
10 There must be random mating Random mating ensures that each organism has an equal chance to pass on its genetic informationRandom Mating AllowedNo Random Mating Allowed
11 B. Large PopulationA large population would limit the effect of Genetic Drift
12 C. No movement into or out of the population Genetically, this would keep the gene pool of a certain population in tact and totally different from nearby gene pools
13 D. No MutationsA mutation would alter the types and numbers of alleles present in the gene pool.
14 E. No natural selectionNo phenotype can have a selective advantage over another.
15 SpeciationThis is the formation of a new species from pre-existing ones.
16 Isolating MechanismsIn order for speciation to occur, there must be an isolation in gene pools between the ‘old’ species and the newer forming species.
17 Reproductive Isolation Once the new species has changed enough where it no longer can share a gene pool with the ‘original species’, both species are said to be reproductively isolated.
18 How does reproductive isolation occur? One way is called BEHAVORIAL ISOLATION.This is when there is a difference in behavior (duh) namely in courtship rituals.Bufo alvariusBufocognatus
19 A second way that isolation can occur is called GEOGRAPHIC ISOLATION. This is where two populations are separated by a geographic barrier.
20 A third way that isolation can occur is Temporal. Temporal isolation is when the two species have a different mating season, duration, etc.
21 Speciation In Darwin’s Finches: Founders ArriveSeparation of PopulationsChanges in the gene poolReproductive isolationEcological CompetitionContinued evolution
22 Final Important Terms Adaptive Radiation – When a single species has evolved into several different forms that live successfully in different ways
23 Convergent Evolution – When two or more unrelated organisms evolve to look like each other.Ex. Aquatic animals (sharks, dolphins, etc.)
24 Coevolution –Two species evolve in response to changes in each other over time.