Natural Selection

NATURAL SELECTION Ch 14 p. 296-324 BEYOND NATURAL SELECTION We now understand that natural selection is just ONE of a number of processes that can lead to evolution. THE SYNTHETIC THEORY OF EVOLUTION = a combo of Charles Darwins Natural Selection & Gregory Mendels Genetic Inheritance

along with population genetics and molecular biology of the 20th century NATURAL SELECTION Genes are the carriers of inheritable characteristics They are also the source of random variation upon which natural selection operates Mutation causes some variation Meiosis is when most variation occurs during

the copying, shuffling and dealing of genes to the gametes and crossing over Remember, genetic variation is random, it is not controlled or directed toward a goal How Natural Selection Works In the struggle for survival, entire organisms, not genes, either survive & reproduce, or do not

Natural Selection operates on the phenotypic variation between individuals Phenotypic = physical & behavioral characteristics produced by the interaction of genotype & environment How Natural Selection Works More fit individuals will have more success mating and will live longer

therefore producing more offspring in the next generation In essence, this is selection because individuals who are phenotypically fit will produce more offspring, thus causing a change in the genetics of the next generation EVOLUTION AS GENETIC CHANGE POPULATIONS: individuals of the same species in an area who breed with one another

GENE POOL: all of the alleles of genes within a population RELATIVE FREQUENCY: number of times an allele appears in a population compared to the other alleles of the same gene EVOLUTIONARY CHANGE INVOLVES A CHANGE IN THE RELATIVE FREQUENCIES OF ALLELES IN THE GENE POOL OF A POPULATION POPULATION GENETICS Study of genetic traits in

individuals Genotype actual allele inherited from each parent that the individual has (blue eyes, brown eyes) Phenotype resulting observable characteristic from the interaction of the individuals genotype (brown eyes)

POPULATION GENETICS Study of genetic traits in populations Gene Pool: combined genetic material of all the members of a population Alleles: name for the 2 or more different forms of a gene. (gene = eye color, alleles = blue, brown, green ) Allele Frequency: is a fraction that represents the frequency of a particular allele within a population HARDY-WEINBERG PRINCIPLE 1. If a population is not evolving, allele frequencies are

in Genetic Equilibrium Under specific conditions allele frq. Remain constant If those conditions are not met the population may EVOLVE 2. Conditions required to maintain G.E. are: No natural selection Random mating

No migration No mutation Very large population size If all these conditions are met, and the allele frequencies are not changing between generations, then the population is in HardyWeinberg equilibrium and is not evolving. In nature, one or more of these assumptions is always being violated. Real populations are compared against the Hardy-Weinberg

model to see if they are evolving MECHANISMS OF EVOLUTION Mechanisms of Evolution 1 Natural Selection Over-reproduction + Variation Competition Competition for survival & REPRODUCTION Heredity to next

generation Mechanisms of Evolution 2 Mutations = source of genetic variation change in the DNA sequence within a gene or chromosome of a living organism. Can be Neutral, Harmful

or Beneficial to fitness of the individual Germline mutations = gametes (eggs or sperm cells) can be pass on to offspring Somatic mutations = non-reproductive cells are not pass on to the

following generation. Mechanisms of Evolution 3 GENETIC DRIFT Random change in allele frequency due to a random event Does not necessarily result in ADAPTIVE evolution Occurs more/ Has more impact on SMALL

populations Two main types or Genetic Drift = Bottle Neck Effect Founders Effect Types of Genetic Drift Bottle Neck Effect Founders Effect

Mechanisms of Evolution 4 Gene Flow Migration the transfer of genes from the gene pool of one population to another may change the frequency and/or the range of alleles in the The introduction of new alleles increases variability within a population and allows for new combinations of traits.

DISTRUBUTION & TYPES of SELECTION The normal distribution of variations in a population can change by natural selection Evolution results from disruptions in genetic equilibrium STABALIZING SELECTION This is selection against the extreme phenotypes and may result in reduced

variability over time DIRECTIONAL SELECTION This type of selection occurs when a change in the environment makes it infavorable to have an extreme phenotype

DISRUPTIVE SLELECTION This type of selection occurs when an environmental change makes it unfavorable to have the most common phenotype CONCEPT OF A SPECIES Speciation and extinction were extremely important in

determining the history of life on earth Before we can know whether speciation has occurred in a group of organisms, we have to know what a species is! A species is a group of interbreeding individuals or populations that are reproductively isolated from other such groups SPECIATION Speciation involves environmental processes that lead to

the splitting of a gene pool into two or more separate pools MAJOR CAUSES: Reproductive isolating mechanisms Geographic isolation Courtship behaviours SPECIATION - REPODUCTIVE ISOLATING MECHANISMS The key event in PRE-ZYGOTIC = speciation is

Prevent fertilization Reproductive Seasonal/habitat barriers to mating, behavioral isolation, Isolation between physical isolation two diverging POST-ZYGOTIC = populations Come into play despite Isolating mechanisms fertilization Gamete mortality, hybrid nonare all genetically

viability, hybrid sterility based and can be either pre-zygotic or post-zygotic SPECIATION ISOLATION - GEOGRAPHIC Simplest mechanism of isolation Continents collide, mountains are uplifted &

suddenly a population finds that it is splintered into a large population as well a number of geographically isolated smaller population Most of these small populations eventually go extinct SPECIATION BEHAVIORS - COURTSHIP

Often the behaviors a male must engage in to convince the female of his proper species-hood are quite elaborate and cannot be reproduced by member of a different species Various behavioral cues allow males & females to recognize their own species PUNCTUATED EQUILIBRIUM VS GRADUALISM Darwin saw evolution as a slow, continuous process, without sudden jumps (GRADUALSIM) however, if you

study the fossil record, you will see long intervals in which nothing changed (EQUILLIBRIUM) punctuated by short, revolutionary transitions in which species became extinct and replaced by new forms (PUNCTUATED EQUILIBRIUM) Instead of a slow progression, evolution of life seems more like the life of a fire-fighter: long periods of boredom interrupted by rare moments of terror. TYPES OF EVOLUTION The basic evolutionary mechanisms-mutation,

migration, genetic drift, and natural selection- can produce major evolutionary can change if given enough time THERE ARE 3 MAJOR TYPES OF EVOLUTION: Divergent Convergent Co-evolution DIVERGENT EVOLUTION = THE PROCESS OF 2+ RELATED SPECIES BECOMING MORE DISSIMILAR

Ex. Red Fox (forests, red) and Kit Fox (prairies, tan) Similarities in structure show that they have a common ancestor, but as they adapted to different environments, they diverged CONVERGENT EVOLUTION = WHEN ORGANISMS THAT ARE NOT CLOSLY RELATED EVOLVE SIMILAR TRAITS Ex. Antifreeze proteins in both Antarctic and Arctic fish

Ex. Wings of a bat and bird COEVOLUTION = JOINT CHANGE IN 2+ SPECIES IN CLOSE INTERACTION Often occurs between Predators and prey Parasites and hosts Ex. Plants and the animals that pollinate them

EXTINCTION 99% of the species that have ever lived on earth have gone extinct! Present day biodiversity is a result of an accumulation of changes due to extinction events over millions of years EXTINCTION

CONTAINS 3 KEY ELEMENTS: For geographically widespread species extinction is rare Large mass extinctions produce major restructuring of the biosphere and allowing previously minor groups of expand and

diversify It is generally impossible to predict which species will be victims of an extinction event SUMMARY EVOLUTION CAN RESULT FROM: Mutation Natural selection

Genetic recombination Non-random mating Genetic drift Gene flow Extinction EVOLUTIONARY PROCESSES ALLOWS US TO UNDERSTAND:

Crossing over Mutation Extinction Convergent evolution Divergent evolution Co-evolution

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