Unit Four
Mutations
 Any alteration in the base sequence of DNA—Errors can occur during DNA replication.
 Most discovered and corrected by proof reading enzymes.
 Some still are missed.
 Theoretical basis for Natural Selection.
Types Of Mutations
Point Mutation
 The substitution of one base for another.
 AAAICGGCAAACCGGC
 TTTAGCCGTTTGGCCG
 Replacing the “T” with a “C” changes the T/A pair to a C/G pair.
 The particular change would alter the amino acids for the codon from SER to GLY.
 May or may not affect the functioning of the protein.
 The effect may be positive; i.e., a change which results in a more efficient protein.
Silent Mutation
 An alteration of the DNA sequence which does not alter the amino acid sequence.
o Remember the codon table there are usually more than one codon for each amino
acid. (Same protein produced - mutation has no effect).
 AAAGAGAAAGAA
 TTTCTC TTTCTT
Frame Shift Mutation
o Insertion or deletion of a DNA base shifts the reading frame for the entire downstream
sequence. (Small insertion or deletion).
o Alters virtually every codon. (Thymadine dimmers).
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o Results in a nonfunctional protein.
Addition/Deletion
o Large insertion or deletion of DNA results in nonfunctional protein.
Somatic Cell Mutation
o Somatic cells—Every cell in your body that is not a sex cell (sperm/egg).
o These mutations not passed along to offspring.
o Result most often from external damage.
o Precursor to cancer.
Germ Cell Mutation
o Mutation in egg/sperm.
o Passed on to offspring.
o `Basis for Natural Selection.
o Why does changing the A.A. change the protein?
o 20 Amino Acids
o Each has own unique shape and properties.
o Proteins fold into 3-D shape and specific active sites.
o Altering the A.A. may disrupt either the 3-D shape or the active site.
Causes Of Mutations
o Internal
o Defective DNA polymerase. (Makes more DNA).
o Error/proof reading enzymes.
o External Mutation
o Gamma rays
o UV radiation
o Free radicals
o Carcinogens—any substance which causes DNA damage.
Darwin’s Theory Of Selection
 Darwin a Naturalist sailed on the Beagle5 yr. tripEnglandSouth AmericaNew
ZealandAustraliaSouth AmericaEngland.
 Collected living specimen and fossils throughout the trip.
 Fossils were similar but not identical to current living organisms.
 Observed that characteristics varied within the same species in different populations.
Natural Selection
 Those individuals better equipped to survive will reproduce at a higher rate and with greater
success.
 Overtime the traits of these individuals will accumulate in a given population.
 Eventually a new species:
o E.g., Differences in beak shape and size arose in varying population to exploit
different food sources.
 Species isolation leads to differentiation.
 Species one defined by their ability to mate and reproduce viable offspring.
 Horse + donkey = MuleSterile.
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What Is Selection?
Natural Selection:
 The environment chooses which individual survives.
 Those better equipped will send their DNA into the next generation.
Artificial Selection:
 Man chooses which individual will send their DNA into the next generation.
 Select those individuals which passes the traits which you find desirable.
o E.g., Dogs, descended from wolves.
Types Of Selection
Stabilizing:
 Selection for the average.
 Selection against the extreme.
 Chicken & ducks—Eggs of intermediate weight have best hatching success.
Directional:
 Selection for one extreme & against the other extreme.
 Humans—Height is increasing generation after generation.
Disruptive: (Least Common)
 Selection for extremes.
 Selection against the average.
 Nonpoisonous butterfly mimics the color marking of the poisonous one.
 Those who are completely successful survive.
 Those butterflies who miss by a little are eaten by predators.
Natural SelectionEvolution
 The better suited individuals produce more offspring.
 Their DNA passed down more often & with more success.
 These traits soon predominate in the population.
 Leads to new species development over time.
Lamarck’s TheoryAcquired Characteristics
 Abilities developed in the current generation would be passed on to the next generation:
o Example: Giraffes stretched their necks to reach food so next generation would be
born with stretched necks.
 Does not account for new species generation.
Hardy Weinberg (Where Math meets Biology)
 Allele frequency remains unchanged over time.
 For this to be true the following assumptions must be met:
1. Very large population.
2. Random mating.
3. No mutation.
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4. No migration into or out from the population.
5. No Natural Selection.
May seem restrictive but if the population is large enough the other conditions have a
minimal impact.
o P=Dominant allele q=Recessive allele
P2 + 2Pq + q2 = 100% of population.
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HD Het hr
HD = Homozygous Dominant
Het = Heterozygous
hr = Homozygous Recessive
If I give you the frequency of homozygous recessive can you determine the allele frequencies?
If 5% of population has polydactaly, a recessive disorder of extra fingers What are the allele
frequencies for this population?
P + q =1
(Professor will complete calculation of allele frequencies using the formula p2 + 2 pq + q2 = 1 )
What factors may affect HW equilibrium?
Random Mating
 Each individual must have an equal chance of mating with every other individual.
 Utilizing criteria for choosing a mate can affect allele frequencies.
Mutation
 Alteration of DNA.
 Usually at such low frequency it does not directly affect the allele frequencies from one
generation to the next.
Migration
 Movement of individual(s) into or out from a population.
 Depending on the size of the population & the size of migration can affect Hardy Weinberg
Theory.
Natural Selection
 Applying pressure which selects a set of individuals will definitely alter allele frequencies.
 Like mutation, however, it occurs in general very slowly so as not to alter allele frequencies
from one generation to the next.
Hardy Weinberg Busters
Genetic Drift:
 Characteristics of very small populations.
 If an allele has a very low frequency it can be lost from a population in a single generation.
 A single individual not mating can remove the allele.
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Founder Effect
 Small group of individuals migrate to begin new population.
 Only those alleles in the founders will be represented in the resulting population.
 May have very different allele frequencies than the original generation.
Amish
Bottle Neck Effect
 Same outcome as the founder effect.
 Population decimated by natural disaster.
 Only small number remain.
 New population will only have the alleles from the survivors.
 Cheetahs—All cheetahs are virtually genetically identical.
Non Random Mating
 Inbreeding
 Results in an increase of homozygous individuals
Life Forms Are Categorized Into Six Kingdoms
1. Archaebacteria.
2. Eubacteria.
3. Prostista.
4. Fungi.
5. Plantae.
6. Animalia.
Populations
 Individuals of the same species in the same location.
o Southeastern Pennsylvania White tail Deer.
Communities
 Population of different species in the same location:
o Deer, trees, grass, insects, bears, Mountain Lions in Pocono Forest.
Ecosystems
 Community plus its non-living regions.
o Elevations, soil types, rainfall, temperature, etc.
o Deer, trees, grass, insects, Mountain Lion in Pocono Mountain Forest.
Biomes
 Large geographical regions of similar characteristics:
o Desert, Tropical Rain Forest, Deciduous Forest, prairie.
 The Pocono Mountain Forest has much in common with the Colorado Deciduous Forest.
Food Webs
 ProducersMake their own food.
 ConsumersEat other life forms.
PlantsProducers.
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Harness energy from the sun.
Light reactions versus Dark reactions.
Herbivores
 Eat plants.
 Primary consumers.
Carnivores
 Eat animals.
 Secondary consumers.
 Primary consumers.
Omnivores
 Eat plants and animals.
Decomposers
 Recycle dead organic matter (plants and animals).
 Bacteria, fungi, insects, worms.
**Energy decreases as you go up in the food web.
**Number of individuals decreases as you go up in the food web.
Planetary Cycles
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Water Cycles
o Water cycles back and forth.
o Between the atmosphere.
o And the surface of the planes.
Sublimation - Ice and snow skip the liquid stage and can directly add H2O to the
atmosphere.
Liquid water from lakes, rivers and oceans evaporate into atmosphere.
Water returns to the surface via precipitation.
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Carbon Cycle
 Plants remove CO2 from the atmosphere in photosynthesis
 CO2 in atmosphere diffuses into oceans.
o What role does the temperature of the ocean play in this ability?
 CO 2 released to atmosphere by:
1. Cellular respiration.
2. Burning of fossil fuels.
3. Decomposition of organic materials.
It is quite possible that man will exceed the planet’s ability to support us.
Global Warming …
 Mean rise in the earth’s temperature of 1o Fahrenheit in the last century
 CO 2 emissions increase the greenhouse effect, allowing sunlight in, but preventing some of the
resulting heat from radiating back to space.
 Is it real?
o Polar ice forms later and melts earlier
o Glaciers are retreating
o Sea levels are rising
Which species are currently threatened by a warming shift in the climate? (don’t forget plants too)
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