1. Ch. 17
Part 2

2. Evolution Long-term change in the characteristics of a species
Frequency of a particular allele within a population
When a group of organisms change over time
Changes in allele frequency within a population over many generations
Occurs because natural selection gives some alleles a better chance at surviving than other
Over many generations, populations gradually changed
Get better adapted to environment

3. 4 Main Principles of Natural Selection
Variation exists within a population
Organisms compete for limited resources
Organisms produce more offspring than can actually survive
Individuals with variations suitable for their habitat are the ones that SURVIVE and REPRODUCE

4. Three Major Types of Selection
Stabilizing Selection
Selection pressures are on the two extreme phenotypes
Center range/mean phenotype (average) is favored
Variation centered around mean value
Environment is stable
If organisms are well adapted to the environment, most common alleles in the population will lead to an advantage on the organisms and alleles wil continue to be passed on
Directional Selection
Aka EVOLUTIONARY SELECTION
Occurs when new environmental factor or new allele appears within a population
Results in change of characteristic in ONE particular direction
ONE specific phenotype is favored
Disruptive Selection
Occurs when conditions favor both extreme phenotypes of a population
Maintains different phenotypes with the population
Polymorphism

5. 1. Stabilizing Selection
Favors the more common traits in a population as opposed to the more EXTREME or unusual traits
Eliminates individuals that have EXTREME or unusual traits
Maintains the existing population frequencies of common traits while selecting against all other trait variations
Example: Infant birth weight

7. 2. Directional selection
Favors traits at one EXTREME of the range of possible traits
Result:
traits at the opposite end disappear
If this continues for many generations, favored traits become more and more extreme
Result: distinct changes in allele frequencies of the population
Examples:
Insecticide resistance
Peppered moth

9. 3. Disruptive Selection
Environment favors more EXTREME or UNUSUAL traits over common traits
Extreme or unusual traits at both ends of the spectrum are favored…common traits disappear over time
Leads to BALANCED POLYMORPHISM
Population divided into two phenotypes

13. Mutations
CAUSES:
Spontaneous
Natural factors
Ultraviolet radiation from the sun
Exposure to chemicals
Exposure to radiation
Introduces new alleles into a gene pool that NEVER existed before
VITAL b/c provides source for new variation
What is a mutation:
Change to an organisms genetic material (DNA)
Change the NUCLEIC ACIDS that make up one or more genes
Changes can produce new traits that can either HELP or HURT the survival of an organism
BENEFICIAL Mutations help organism
NEUTRAL Mutations have no effect on organism
NEGATIVE Mutations hurt organisms chances for survival

14. New Environmental Factors
Environmental changes can make certain phenotypes that were once NOT beneficial suddenly become beneficial
Ex. Ice age
Rabbit fur
Agouti brown originally favored
New environment makes white fur more beneficial
Frequency of the allele for white fur increases at the expense of the allele for agouti brown fur
Result after many generations?
Many white furred rabbits
Changes in environmental factors ONLY affect the likelihood of an allele surviving in a population
Environmental factors do NOT affect the likelihood of an allele arising by mutations

15. Antibiotic Resistance
Antibiotics chemicals produced by living organisms that inhibit or kill bacteria but do NOT harm human tissue
Most produced by fungi
Penicillin  1st antibiotic
Produced by fungus Penicillium
Treats wide range of bacteria
Stops cell wall formation  prevents bacterial cell reproduction
Kills all bacteria sensitive to penicillin
Inhibitor of enzymes called glycopeptidases
Glycopeptidases used to form cross-links between peptidoglycan molecules in cell walls of bacteria; makes cell wall rigid so cell do not burst when taking up water
Hopefully the ENTIRE population
What happens when entire population is NOT killed by antibiotic?
Due to one or more individual bacteria carrying an allele that makes them resistant to penicillin
NOT GOOD
Bacterial DNA
Single loop of DNA
Only ONE copy of each gene
Mutant alleles have IMMEDIATE effect on phenotype
Provides bacteria with selective advantage (those with beneficial allele will survive and reproduce…those without will die) if there are ideal conditions
Bacteria divide rapidly by BINARY FISSION

16. Antibiotic Resistance
Arises when an existing gene with the bacterial genome changes (mutates) spontaneously to give rise to a nucleotide sequence that codes for a slightly different protein that is NOT affected by antibiotic
DNA MUTATION!!!!
Incorrect dosage or stopping a cycle of antibiotic treatment increase chances of antibiotic resistant bacteria

17. Penicillin Resistant Bacteria
Produces enzymes that make penicillin ineffective against them
B lactamase
Group of Enzymes that breaks apart the penicillin molecule
Penicillinase
Enzyme that inactivates penicillin
Staphylococcus
Cause Staph Infection
may cause disease due to direct infection or due to the production of toxins by the bacteria
Methicillin-resistant Staphylococcus aureus
MRSA type of Staphylococcus aureus that is resistant to the antibiotic methicillin and other drugs in this class (penicillin)

18. Human Use of Antibiotics
Antibiotic use  change in environmental factors of bacteria
Exert selection pressures on bacteria
Enable more antibiotic bacteria t proliferate
Constantly trying to find new antibiotics that bacteria are NOT resistant to
More humans use antibiotics = greater selection pressures exerted on bacteria to evolve resistance to antibiotics
BAD!

19. Bacteria can pass off genes to other bacteria increase proliferation of resistant bacteria

20. Pollution from Sulfur Dioxide Released into the Air = no more lichens
Industrial Melanism
Pollution from Sulfur Dioxide Released into the Air = no more lichens
Example of changing environmental factor
Peppered Moth Biston betularia in UK and Ireland
Night-flying
During the day found on branches of tress to camouflage from insect eating birds (sight hunters)
Before 1849
Pale wings with dark markings
In 1849
Black (melanic) moth found
Population of melanic moth increased in certain areas
Difference between Speckled and Melanic Moths
One gene
Normal speckled coloring recessive allele c
Black coloring  dominant allele C
Frequency of dominant C allele increased in areas near industrial cities
Frequency of recessive c allele increased in non-industrial areas
Selection pressure causing change in allele frequency in industrial areas  predation by birds
Unpolluted (non-industrial) areas  green, brown, and grey lichens covered tree branches = good cover for speckled moths
Polluted (industrial) areas  sulfur dioxide affects lichens  lichens do NOT grow on trees = dark bark presides = good cover for melanic moths

21. 1970s decrease in pollutants = change in melanic allele frequencies
Mutated C alleles were always present in moth population
Those with dominant C allele never survived because they were always spotted by the predatory birds and eaten (and never passed off their genes)
Dominant C allele only increased its frequency when having dark pigment gave moths advantage in polluted areas
Mutations to the C allele NOT caused by pollution
Changes in environmental factors ONLY affect the likelihood of an allele surviving in a population
Environmental factors do NOT affect the likelihood of an allele arising by mutations

22. Malaria Review Caused by protoctist parasite Plasmodium
Insect vector  mosquito (salivary glands)
Mosquito bites  Plasmodium enters blood
Parasite enters RBCs  multiplies in RBCs  illness and death

23. Sickle Cell Anemia and Malaria
HBS (sickled hemoglobin) and HBA (normal hemoglobin) alleles
Possible genotypes:
HBSHBS (homozygous dominant, sickled RBCs)
Great selective disadvantage  less likely to survive and reproduce
HBSHBA (heterozygous dominant, some sickled RBCs, carriers)
Less likely to suffer from serious attack of malaria
Contain about 1/3rd the number of Plasmodium parasites is their blood compared to homozygous normal HBAHBA
HBAHBA (homozygous dominant  normal)
More likely to suffered from serious attack of malaria
Parts of the world with increased cases of MALARIA have higher frequency of HBS (sickled hemoglobin) allele

25. Two Strong Selection Pressures Acting on 2 Alleles
HBSHBS
Selection against these genotypes b/c they become seriously anemic
HBAHBA
Selection against these genotypes b/c they are more likely to die from malaria
HBAHBs
Strong selection advantage
Do not suffer from sickle cell anemia
Less likely to suffer from malaria
Both alleles remain in population where MALARIA is an important environmental factor

27. More noticeable when a small # of individuals are separated from the rest of the population
Form small sample of original population
Not likely to have same allele frequencies as large population
Further genetic drift in small population  alters allele frequencies even more
Evolution of small population may be very different from evolution of larger population
Process called FOUDNERS EFFECT (occurs in small, isolated populations)
Genetic Drift

28. Genetic Drift Founder Effect Bottleneck Effect
When allele frequency of group of migrating individuals, by CHANCE, are different from their original population
Bottleneck Effect
Occurs when a population undergoes a dramatic decease in size
Regardless of cause of bottleneck (natural disaster, predation, disease), small population is now very vulnerable to genetic drift
Certain alleles have greater effect on population than other alleles
The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better adapted” individuals. That, in a nutshell, is genetic drift.

29. Genetic Drift
changes in the allele frequency within a population that occur by chance
genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better adapted” individuals
No guarantee that the new population will be better suited to its environment than the original population
Effect of Genetic drift is very strong and dramatically influences evolution of small populations (fewer than 100)
Before
After
The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better adapted” individuals. That, in a nutshell, is genetic drift.

30. Allele frequencies measure genetic variation.
how common allele is in population
can be calculated for each allele in gene pool
Calculate the allele frequency for G(Green frogs) in the population
Calculate the allele frequency for g (brown frogs) in the population

31. How to calculate the ALLELE Frequency in a Gene Pool
Allele X or Allele x for certain TRAIT
Allele frequency X = # of allele X in population (gene pool)
total # of alleles (X + x) in population (gene pool)

32. Hardy Weinberg Principle (HWP)
Phenotypes controlled by 2 alleles only (A and a)
Three possible genotypes:
Homozygous DOMINANT (AA)
Heterozygous DOMINANT (Aa)
Homozygous RECESSIVE (aa)
Two phenotypes:
Dominant (can be AA or Aa)
Recessive (HAS to be aa)
HWP allows the proportions of each genotype in a large, randomly mating population to be calculated
Total population = 100% or 1
Frequencies within population are rations or percentages of whole population (decimals or percentages)
P = frequency of dominant allele in population
Q = frequency of recessive allele in population
P + Q = 1 (all the alleles in the population)
P2 = frequency of homozygous dominant allele in population
Q2 = frequency of homozygous recessive allele in frequency in population (easy to recognize)
2pq = frequency of heterozygous genotypes in population

33. Condition when the HWP does NOT apply to a population
Purpose of HWP
Condition when the HWP does NOT apply to a population
When to use HWP:
Determining ratios of different genotypes in population allows predication of their ratios in the next generation to be compared with observed results
Use Chi-Squared test to analyze significance
Significant differences mean:
Evidence of directional selection occurring in population (only if migration and non-random mating can be discounted)
Small populations
Significant selective pressures against one particular genotype
Migration of Individuals carrying one of the two alleles into OR out of population
Non-random mating

34. Practice Problem

36. Practice Problem