MICROEVOLUTION MICROEVOLUTION VS. VS. MACROEVOLUTIONMACROEVOLUTION

• Microevolution: survival through the inheritance of favorable characteristics – mutations – selection

• Macroevolution: progression of biodiversity through geological time – speciation – extinction

MICROEVOLUTIONMICROEVOLUTION

Evolutionary Mechanisms

Types of Natural Selection

Hardy-Weinberg Equilibrium

WHAT IS WHAT IS MICROMICROEVOLUTION?EVOLUTION?

• Traces generational changes in a population of organisms

• Changes eh?– Allelic frequency changes within a

gene pool!

•

WHAT LEADS TO CHANGES WHAT LEADS TO CHANGES IN THE GENE POOL OF A IN THE GENE POOL OF A

POPULATION?POPULATION?• SMALL POPULATION SIZE

(small pop frequencies)

toss a coin to prove it.

MECHANISMS OF MECHANISMS OF EVOLUTIONEVOLUTION

• GENETIC DRIFT

(random/chance events that change the gene pool of a small population)

examples:

natural disasters

2 TYPES OF GENETIC DRIFT 2 TYPES OF GENETIC DRIFT MECHANISMSMECHANISMS

• Genetic Bottleneck

dramatic decrease in pop size due to :

catastrophes

predation

disease, etc.

• Founder Effectmigration leads to changes in allele

frequencies from population of origin

WHAT ELSE CAUSES GENE WHAT ELSE CAUSES GENE POOL CHANGES ?POOL CHANGES ?

• GENE FLOW

immigration

emigration

EX OF GENE FLOW IN EX OF GENE FLOW IN HUMANSHUMANS

• Frequency of Rh- allele among Africans:

63%

• Frequency of Rh- allele among

African-Americans

45%

• Frequency of Rh- allele among White European population

3%

• MUTATIONS

may produce a selective advantage

may produce deleterious effects

may be harmless

• NATURAL SELECTION!

increases/decreases allele frequencies due to environmental impact.

Ex: English Peppered Moths

• NON-RANDOM MATING

individuals choose based upon traits

(vertebrates)

individuals “choose” based upon

physical proximity

(invertebrates)

OTHER FORMS OF NON-OTHER FORMS OF NON-RANDOM MATING:RANDOM MATING:

• INBREEDING– Proximity issues

• SEXUAL SELECTION:1. Male competition:

# offspring fitness2. Female choice: quality offspring fitness

SEXUAL SEXUAL SELECTIONSELECTION

Picky females, show-off males…

MICROEVOLUTION REVIEWMICROEVOLUTION REVIEW

• Changes in the GENE POOL!

• Caused by:– Gene Flow– Natural Selection – Mutations– Non-Random Mating

• Sexual Selection• Inbreeding

THE SIGNIFICANCE OF THE SIGNIFICANCE OF SELECTIONSELECTION

• Selection increases the adaptive qualities of a population for the environment in which it lives.Types of Selection:

Natural Selection determined by phenotype selection toward phenotypes that

improve fitness

SUBDIVISIONS OF NATURAL SUBDIVISIONS OF NATURAL SELECTION…SELECTION…

Stabilizing Selection

Eliminates individuals with extreme traits. Results in decreased variation

Directional Selection

Favors traits at ONE extreme

ex: resistance to insecticides

DIRECTIONAL SELECTIONDIRECTIONAL SELECTION

                                                               

Disruptive Selection

Selection toward BOTH extremes. Extreme traits are favored, common traits are NOT!

Results in major divisions in population!

What might result?

DISRUPTIVE SELECTIONDISRUPTIVE SELECTION

                                                               

ARTIFICIAL ARTIFICIAL SELECTIONSELECTION

Directional selection determined by humans

CAUSES OF VARIATIONCAUSES OF VARIATION

• Mutation is the ultimate source of variation

• Two major types of mutations:–Gene mutations

–Chromosome mutations

GENE MUTATIONSGENE MUTATIONS

Addition / Insertion

Deletion

Substitution

Inversion

SPECIFIC EXAMPLES OF SPECIFIC EXAMPLES OF MUTATIONSMUTATIONS

• Gene mutations–PKU (phenylketonuria)

–CF (cystic fibrosis)

• Chromosome mutation–Klinefelter syndrome (male with

47,XXY karyotype)

ONCE MUTATIONS HAVE ONCE MUTATIONS HAVE ARISEN, FURTHER ARISEN, FURTHER

VARIATION RESULTS FROM:VARIATION RESULTS FROM:• Recombination of

alleles during meiosis

• Recombination of alleles during fertilization

ONCE GENETIC ONCE GENETIC VARIATION HAS ARISEN, VARIATION HAS ARISEN,

THERE IS ALSO THERE IS ALSO PHENOTYPIC VARIATION.PHENOTYPIC VARIATION.

• Recall that, according to Darwin’s Theory, due to competition within populations, there is …

Differential Reproduction of Selected Phenotypes

GREAT EXAMPLE OF GREAT EXAMPLE OF DIFFERENTIAL DIFFERENTIAL

REPRODUCTION OF REPRODUCTION OF SELECTED PHENOTYPES:SELECTED PHENOTYPES:

ULTIMATE RESULT OF ULTIMATE RESULT OF EVOLUTIONEVOLUTION

Change in the genetic composition (gene pool) of a

population.

RELATED CAUSES OF RELATED CAUSES OF GENETIC VARIATIONGENETIC VARIATION

Sexual Reproduction!

• Diploidy

• Outbreeding

MINORITY ADVANTAGE…MINORITY ADVANTAGE…

• 50/50 Sex Ratio

• Predation (more common phenotype preferred by predator)

• The Lefty Hypothesis

10-15 % general population

>50% contact sports (esp. males)

REPRODUCTIVE ISOLATIONREPRODUCTIVE ISOLATION

Prezygotic

• Temporal isolation

• Behavioral isolation

• Mechanical isolation

• Ecological isolation

• Gametic isolation

Postzygotic

• Hybrid inviability

• Hybrid sterility

• Hybrid breakdown

ALLOPATRIC SPECIATIONALLOPATRIC SPECIATION

SYMPATRIC SPECIATIONSYMPATRIC SPECIATION

GRADUALISMGRADUALISM

Species A evolves to become species B.

LONG, GRADUAL process!

PUNCTUATED PUNCTUATED EQUILIBRIUMEQUILIBRIUM

• Evolution is Slow with brief periods of rapid development of new species.

THE HARDY WEINBERG LAWTHE HARDY WEINBERG LAW

• If allele frequencies for a population do not change…

NO EVOLUTION IS OCCURRING!

• Genetic Equilibrium

• Hardy Weinberg Equilibrium

GENETIC EQUILIBRIUM GENETIC EQUILIBRIUM OCCURS ONLY IF THERE IS…OCCURS ONLY IF THERE IS…

1.A large breeding population 2.Random mating 3.No change in allelic frequen

cy due to mutation

4.No immigration or emigration

5.No natural selection

EQUILIBRIUM REQUIRES…EQUILIBRIUM REQUIRES…

• Large Population Size(laws of probability must apply)

• Isolation of Population(no immigration/emigration to/from other populations)

• NO MUTATIONS ALLOWED!• NO NATURAL SELECTION ! all traits must be selectively neutral• Mating Must Be RANDOM equal probabilities of mating btwn genotypes

IS HW EQUILIBRIUM IS HW EQUILIBRIUM POSSIBLE?POSSIBLE?

• YES ? / NO ?

• WHY / WHY NOT??

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

THE HARDY-WEINBERG THE HARDY-WEINBERG EQUATIONEQUATION

• Given one locus with two alleles (A,a) the frequency of either allele is described by a number from zero to one:

allele absent from pop freq = 0

same allele in all indiv in pop

freq = 1

WHAT IF BOTH ALLELES ARE WHAT IF BOTH ALLELES ARE PRESENT IN A POPULATION?PRESENT IN A POPULATION?• Frequency of both alleles is equal to

p + q = 1

[p = dominant allele (A)]

[q = recessive allele (a)]

• Knowing the frequency of one allele allows for the calculation of the other…

p = 1- q ; q = 1 - p

• If p+q=1,

then (p+q)2 = 1.

Expand it and get…

p 2 + 2pq + q2 = 1

WHAT DOES IT ALL MEAN WHAT DOES IT ALL MEAN GENOTYPICALLY?GENOTYPICALLY?

p2 = frequency of AA

2pq = frequency of Aa

q2 = frequency of aa

PROBLEM 1PROBLEM 1

• In pigs, the allele for black coat (b) is recessive to the allele for pink coat (B).

WHAT % OF PIGS ARE WHAT % OF PIGS ARE HETEROZYGOUS FOR PINK HETEROZYGOUS FOR PINK

COAT?COAT?

PROBLEM 2PROBLEM 2In a certain population of 1000 fruit flies, 640 have red eyes while the remainder have sepia eyes. The sepia eye trait is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color?

PROBLEM 3PROBLEM 3

Phenylketonuria (PKU) is a human metabolic disorder that results in mental retardation if it is untreated in infancy. In the United States, one out of approximately 10,000 babies is born with the disorder. Approximately what percent of the population are heterozygous carriers of the recessive PKU allele?

IF 9% OF AN AFRICAN IF 9% OF AN AFRICAN POPULATION IS BORN POPULATION IS BORN

WITH A SEVERE FORM OF WITH A SEVERE FORM OF SICKLE-CELL ANEMIA (SS), SICKLE-CELL ANEMIA (SS),

WHAT PERCENTAGE OF WHAT PERCENTAGE OF THE POPULATION WILL BE THE POPULATION WILL BE

MORE RESISTANT TO MORE RESISTANT TO MALARIA BECAUSE THEY MALARIA BECAUSE THEY ARE HETEROZYGOUS(SS) ARE HETEROZYGOUS(SS)

FOR THE SICKLE-CELL FOR THE SICKLE-CELL GENE?GENE?