Evolution and
Classification
B Y:
S U S A N A LO N D O N O,
LY N N S E Y N G U Y E N ,
C A M I L L E PAG U I N TO A N D
A LY S S A S I LVA
PART 1 A:
Darwin’s Principles of Natural Selection
1. Variation
2. Overproduction
3. Competition
4. Differential Survival
5. Differential Reproduction
Variation
• Heritable variation within traits
- Sexual recombination
- Mutation
Overproduction & Competition
• Individual organisms produce more offspring than can survive
• Therefore, organisms compete for survival
Differential Survival & Reproduction
• Survival of the fittest
• Survivors reproduce and pass on traits to offspring
- Certain allele frequency increases
- Population evolves
PART 1 B:
Chi – Square Test
1.
Decide on a null hypothesis (there is/isn’t a significant difference between specified
populations, any observed difference being due to sampling or experimental error)
2.
Note your “expected” and “observed” values
3.
Calculate the chi-square
•
4.
Look up the chi-square critical value based on the p-value and degrees of freedom (df)
•
5.
Add the values for all categories -> sum of (o-e) /e
df = number of categories - 1
Determine whether the chi-square value < critical value — if so, the null hypothesis is
accepted; if not, the null hypothesis is rejected
PART 2:
Selection
• Types: Directional, Diversifying
and Stabilizing.
• sexual selection
• -based on variation in sexual
characteristics related to
competition and attraction of
mates
• artificial selection
• -seek individuals with desired
traits to produce more offspring
Causes of Evolution of a Population
• Genetic drift: change in a gene
pool due to chance
• bottleneck effect
• founder effect
• Gene flow
• movement of alleles into and out of
a population
• increases diversity
• Mutations: change in genetic
material; considered to be key
idea for evolutionary change
• Nonrandom mating: specific
choosing of mate; eliminate the
ones who are less-fit
• Natural selection: better
adapted=better reproductive
success
PART 3:
Evidence for Evolution
• Fossil Record
• Comparative Embryology
• -radiometric dating; half-life • -embryonic development
• Comparative Anatomy
• Molecular Biology
• -homologous vs analogous vs • -cytochrome C; universal
vestigial
genetic code
• Comparative Biochemistry
• Biogeography
• -common ancestors,
antibiotic resistance
• -Pangea; plate tectonics;
continental drift
PART 4:
Hardy-Weinberg Equilibrium
The Hardy-Weinberg principle:
• Describes a population that is not evolving
• States that frequencies of alleles and genotypes in a population
remain constant from generation to generation
Hardy – Weinberg Conditions
1.
Large population
2.
Random mating
3.
No migration
4.
No mutation
5.
No selection
1. Large Population
• The bigger the better
• Necessary to reduce chance
occurrences having a significant
effect on allelic and genotypic
frequencies of a population.
What happens if the “large population rule” is broken?
• Genetic drift
•
Due to chance changes in populations causing genotypic
frequencies to change over time
•
Likely to “lose” less common alleles or at least represent
dissimilar gene frequencies relative to the original
population
• Founder effect: increases genetic drift as a few individuals move
to a new, isolated area
• Bottleneck effect: increases genetic drift due to drastic
population reduction (ie. - natural disaster, loss of habitat)
2. Random Mating
• Insures a consistent, random shuffling of genes.
3. No Migration
• Individuals who migrate into (immigration) or out
of (emigration) existing populations cause the
gene frequencies of that population to change.
• What happens if the “no migration rule” is broken?
•
Gene flow: alleles are transferred b/w existing
populations b/c of the movement of individuals
or gametes
4. No Mutation
Mutations ins the genotype cause the most direct change in
gene frequency.
5. No Selection
• Natural / artificial selection ill cause a shift in gene frequencies.
p+q=1
• Percentages are represented as decimal numbers
• p = the dominant allele
• q = the recessive allele
• Accounting for allele frequencies in isolation (p & q)
To get the 2nd equation:
(p + q = 1)^2
Square it
(p + q) ^2 = 1^2
Use the “foil method”
p^2 + 2pq + q^2 = 1
p^2 + 2pq + q^2 = 1
• p^2 = homozygous dominant
• 2pq = heterozygous
• q ^2 = homozygous recessive
• Accounting for phenotype frequencies
• Represents the 3 genotypes of a genetic cross
Part 5 :
Speciation
Biological Species Concept
• “Species are groups
of interbreeding
natural populations
that are
reproductively
isolated from other
such groups.”
– Ernst Mayr
2 Basic Types of Speciation
• Allopatric- geographical isolation
• Sympatric- populations adjust to accommodate different niches
- Adaptive radiation: Galapagos finches
Rate of Speciation
• Gradualism: Darwin(non)adaptive changes
accumulate
• Punctuated equilibrium:
Stephen Gould, Niles
Eldridge- sporadic changes
PART 6:
The Origin of Life
There are 4 scenarios that explain the creation of organic
molecules
1.
Made from inorganic compounds in the atmosphere
2.
Came from outer space as rain
3.
Made from hydrothermal vents in the ocean floor
4.
Made from comets or asteroids that have struck the earth in the
very beginning.
Miller – Urey Experiment
• Miller, a biochemist, used an apparatus to prove is
hypothesis:
• The atmosphere of the early earth resembled a mixture of
inorganic molecules:
•
•
•
•
•
Water (H2O)
Methane (CH4)
Ammonia ( NH3)
Hydrogen (H2)
No oxygen
• The mixture was kept circulating, boiling, condensing the water.
• The gases passed through a chamber containing electrodes .
• By the end of the experiment, paper chromatography was used to
show that the flask contained amino acids and other organic
molecules.
Protobionts and Protocells
Are the origin of cells.
• Protobionts - collection of organic molecules produced abiotically. This are
surrounded by a membrane-like structure.
• Exhibit properties related to life such as metabolism, reproduction,
maintenance of chemical environment in the interior, which is different
from its surroundings.
• Believed to be a key step to the origin of life
• Experiment by Sydney Fox and Aleksandr Oparin demonstrated its
spontaneous formation and the similarity to conditions in earth. The
experiments formed liposomes.
• Examples of Protobionts are: nanobes or nanobacteria
Protobionts and Protocells continue
• Coacervates were taking new materials from the ocean a degraded
material, which contained the basic properties of life. Nucleic acids
taking over the coacervates and replication led to the establishment
of genetic material and the first living systems.
Protobionts and Protocells
• Protocells are large structures enclosed by a membrane. These
structures carry out the basic properties of life.
• It is suggested that self replicating molecules and metabolism
sources appeared together in protocells.
• Vesicles, which separate inside from outside.
• Abiotically produced vesicles can reproduce on their own and grow,
absorb montmotillonite particles, like those on which RNA are
attached. They also contain a semipermeable bilayer and carryout
metabolic processes.
Free Response :
-In terms of climate and geology, Charles Darwin noted that Galapagos
Islands are nearly identical to the Canary Islands. Darwin was struck,
however, by the fact that the Canary Islands, just off the coast of Africa
(200km or 120 miles), contain very few unique species. Whereas the
Galapagos Islands, over 800km (~500 miles) off the coast of South
America, are home to scores of unique species, found nowhere else in
the world. Give a concise evolutionary explanation for why remote
islands would give rise to unique species, while those relatively close to
mainland contain few if any species not found on the mainland.
Answer
remote islands are isolated
- strong selection pressure to adapt to the environment or not survive.
- adaptive radiation colonizing new habitats/niches; first colonizers fill
unoccupied niches
- founder effect & genetic drift; no gene flow
- geographic isolation in allopatric species
- nearby islands share migration with mainland
-gene flow
- migration may mean island population & mainland share gene pool
- may have similar selective pressures as mainland
- similar niches on mainland & island will be populated by same species so
they will experience similar selective pressures therefore few
opportunities for the evolution of new or distinct species