General Biology
Unit Four
Objective One
Charles Darwin
Theory of Natural Selection –”descent
with modification”
Influenced by his voyage on the Beagle, James
Hutton, Charles Lyell, Thomas Malthus and
others
HMS Beagle Voyage
Darwin noticed gradual changes in the same
species as he moved from north to south and
up in elevation, leading to the hypotheses of
gradualism and adaptive traits
James Hutton
Hutton, a geologist, proposed the theory of
gradualism
Darwin took the ideas of Hutton and thought if the
earth can gradually change over long periods of time,
why not organisms?
Charles Lyell
Lyell, a geologist, stated the concept of
uniformitarianism
Darwin took the ideas of Lyell and thought if the
earth can gradually change over long periods of
time, why not organisms?
Thomas Malthus
Malthus was an economist that stated if a
population outgrew its resources, it would
restrain the population
Darwin applied this to organisms
Erasmus Darwin
Darwin was Darwin’s grandfather who
formulated one of the first theories of
evolution
Darwin wrote of life evolving from common
ancestors, but did not present a mechanism
Jean-Baptiste
Lamarck
Lamarck published his theory of evolution the
year Darwin was born
Larmarck’s mechanism of evolution was
“acquired characteristics”
Alfred Wallace
Wallace was a contemporary of Darwin’s and
developed the same theory of natural
selection
Wallace’s letters to Darwin prompted Darwin to
write and publish the theory first
Darwin’s Four Postulates of Natural
Selection
1. Each generation will produce more
offspring than can possibly survive
2. Inherited variations occur due to random
mutations. These can be harmful, helpful
or
3. neutral
Because of limited resources, not all
offspring survive. Those with the most
advantageous variations will survive.
4. The adaptive traits are perpetuated in
the following generations – non-adaptive are
Sources of Evidences for Natural
Selection
Comparative morphology
Comparative biochemistry
Comparative cytology
Biogeography
Sources of Evidences for Natural
Selection
Comparative morphology
- examines the physical features of extinct and
extant organisms
- uses homologous and vestigial structures to
determine phylogeny
- vestigial structures are those that are retained, but
not longer used
Homologous structures
C
a
n
lead to
Divergent
evolution
Analogous structures
indicate
Convergent
evolution
Mutual
adaptations
lead
to
Parallel
evolution
Sources of Evidences for Natural
Selection
Comparative biochemistry
- examines the sequences of amino acids and
nucleotides
- quantifies the similarities among extant organisms
- usually cannot be used on extinct organisms
Sources of Evidences for Natural
Selection
Comparative cytology
- examines the numbers and sizes of chromosomes in
extant organisms
- compares how cells and tissues develop
- usually cannot be used on extinct organisms
Sources of Evidences for Natural
Selection
Biogeography
- examines the geographic distribution of organisms
- implies that we find modern species where they are
because their ancestors lived there
- analyzed in the context of extinct and extant
organisms
Three Traits of Populations
Morphological traits
Physiological traits
Behavioral traits
Microevolution & Macroevolution
Microevolution is the modification of a population
(gene pool) by small changes in allele frequencies
These changes are brought about by mutation, natural
selection, gene flow and genetic drift
Microevolution & Macroevolution
Macroevolution is the appearance and extinction of a
species
Macroevolution is many times the result of
accumulating microevolutionary changes
Microevolution & Macroevolution
Macroevolution tends to span enormous time frames,
whereas microevolution happens rapidly
Hardy-Weinberg
Equilibrium
An unlikely situation
which mathematically
describes what
happens if evolution
does not occur
Produces a baseline
for comparison
Hardy-Weinberg
Equilibrium
Hardy-Weinberg
conditions:
+ large population
+ mating is random
+ no migration,
mutation or
natural selection
Hardy-Weinberg Equilibrium
Hardy-Weinberg Equilibrium
Natural Selection
A gene pool is all the genes found in an entire population
In theory, this is a pool of genetic resources shared by all
members and passed on to the next generation
Natural Selection
Remember, each gene is present in two or more forms
called alleles
These different forms can create a tremendous amount of
variation
Natural Selection
Allele frequency is the abundance of each kind of allele in a
population
Due to the size of a gene pool, the frequency does not
change rapidly, usually taking many generations
Natural Selection
Genetic equilibrium is a theoretical reference point in
which the allele frequency of a given gene remains stable
from one generation to the next
If this stability continues, the population is not evolving in
respect to that gene
Natural Selection
Crossing over, independent assortment, fertilization,
change in chromosome number or structure will lead to
new combinations of genes – BUT NOT NEW GENES!
Natural Selection
Changes in gene frequencies occur through mutations and
gene flow
Natural Selection
Mutations are changes in DNA sequence that can produce
new alleles
Mutations can be lethal, neutral or beneficial
Beneficial mutations are very rare, but can increase fitness
Natural Selection
Population members with the best adaptations (beneficial
genes) are the ones that survive to reproduce
Over many generations the survivor genes can alter the
allele frequencies
Natural Selection
Gene flow is the movement of genes into and out of a
population (gene pool)
Immigration – new genes entering the pool
Emigration – current genes leaving the pool
Natural Selection
Genetic drift is the random change in allele frequency
brought about by chance alone
The larger the population, the less chance of drift
Natural Selection
Genetic drift can be caused by:
inbreeding
~ bottleneck effect
effect
~
~ founders
Natural Selection
Inbreeding – the constant mixing of genes among closely
related individuals
Inbreeding produces the effect of concentrating alleles
found only in the closely related group
Natural Selection
Natural Selection
Founders effect occurs when a small group breaks away
from the original population
The genes carried by these individuals may cause a change
in the allele frequency found in the original population
Natural Selection
Founders effect
Natural
Selection
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Mechanisms
of Selection
Stabilizing Selection
Intermediate forms of a trait are
favored
Extreme forms of a trait are
eliminated
Tends to counteract the effects of
mutations, gene flow & genetic drift
to preserve the most common
phenotype
Directional Selection
Forms of a trait shift toward one
extreme due to environmental
changes
Adaptive mutations can also cause
this shift
Tends to reduce or eliminate the
original most common phenotype
Disruptive Selection
Extreme forms of a trait are favored
Intermediate forms of a trait are
eliminated
Tends to shift to the extreme forms
due to extremes in the environment
Biological Species Definition
A group of populations in which genes
are exchanged through reproductively
isolated mating, producing viable
offspring
Speciation Patterns
Allopatric Speciation
Sympatric Speciation
Parapatric Speciation
Allopatric Speciation
This type of speciation occurs due to the
development of a physical barrier
The physical barrier splits the
population, preventing gene flow
Due to possible differences in the genetic
variations of the new groups, speciation
may occur
Sympatric Speciation
This type of speciation occurs within the
home range of the population
A very slight ecological separation may
influence sexual selection, leading to
speciation
This speciation can also occur in plants
through polyploidy
Parapatric Speciation
This type of speciation occurs when two
neighboring populations become distinct
species
Interbreeding may occur in a hybrid
zone between the two populations
These adjacent populations may evolve
into two distinct species while
maintaining contact along a border
Reproductive Barriers
Prezygotic reproductive isolation
- six forms
Postzygotic reproductive isolation
- two forms
Reproductive Barriers
Evolutionary Patterns
Gradualism – a pattern of slow, steady changes over
a long period of time
This the pattern proposed by Darwin in his theory of
natural selection
Evolutionary Patterns
Punctuated equalibrium – a pattern of long periods
of time with no change, interrupted by short periods
of dramatic change
This pattern was proposed by Stephen J. Gould and
Niles Eldridge
Evolutionary Patterns
Evolutionary Patterns
Punctuated Equilibrium
Gradualism
Geological
Time Scale
Geological Time Scale
Domains
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Eubacteria
Archaea
Eukarya
The Six Kingdom
Classification System
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Prokaryotic
Unicellular (single celled)
All have cell walls
Autotrophic (producer) or
heterotrophic (consumer)
Asexual reproduction (binary fission)
and conjugation (gene mixing)
Prokaryotic
Unicellular (single celled)
All have cell walls
Heterotrophs and chemotrophs
Have some eukaryotic like genes and
live in extreme conditions
Asexual reproduction (binary fission)
and conjugation (gene mixing)
Eukaryotic
Unicellular (single celled)
Many have cell walls
Autotrophic (producer) or
heterotrophic (consumer)
Asexual reproduction (binary fission)
and conjugation (gene mixing)
Eukaryotic
Multicellular (most)
All have cell walls
Heterotrophic (consumer)
Sessile
Asexual & sexual
reproduction
Eukaryotic
Multicellular
All have cell walls
Autotrophic (producer)
Sessile
Asexual & sexual
reproduction
Eukaryotic
Multicellular
None have cell walls
Heterotrophic (consumer)
Capable of movement
Asexual & sexual
reproduction
Carolus Linnaeus
“The Father of Modern Taxonomy”
Hierarchical system of taxa
Latinized names
Binomial nomenclature
The scientific name
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Eukarya
Animalia
Chordata
Mammalia
Carnivora
Felidae
Panthera
leo
Panthera leo
Viruses
Viruses are non-living structures that are obligatory
parasites of living cells
Viruses are cell specific, causing a variety of diseases
in almost all organisms
Viruses
Viruses are considered non-living because of the
following:
* not made of cells
* no organelles
* cannot metabolize
* they replicate, not
reproduce
Viruses
All viruses are comprised of a nucleic acid
encapsulated by protein
The nucleic acid can be DNA or RNA and may be
single or double stranded
Viruses
The proteins form a coat around the nucleic acid
called a capsid
Some viruses will also have an envelope made of the
cell membrane stolen from a host cell
Viruses
Viruses are very small and come in a variety of shapes
* liver cell = 20µm
RBC = 8µm
E. coli = 2µm
typical virus = .02µm
Viruses
Viral Replication Cycles
Viral Replication Cycles
Viral Replication Cycles
Retroviruses
Viral Infections
Treatment for viral infections is to let it run its course
while treating the symptoms
Preventative treatment is by way of vaccines
Prokaryotic Cells
Prokaryotic Cells
Coccus
Bacillus
Spirillus
Bacterial Metabolism
Bacterial metabolism exhibits a
number of different strategies:
~ photosynthesizers
~ heterotrophic consumers
~ aerobic & anaerobic respiration
Bacterial Reproduction
Bacteria increase in numbers using
a form of asexual reproduction
called binary fission
Bacteria produce genetic diversity
through a process called
conjugation
Ecological Impact of Bacteria
Bacteria have three major
ecological impacts:
~ decomposers (vast majority)
~ nitrogen fixers
~ pathogens
Ecological Impact of Bacteria
Most bacteria are decomposers,
breaking down dead organisms,
lost or shed organismal parts &
organic wastes
Bacterial decomposers break down
organic compounds into their
elemental states
Ecological Impact of Bacteria
Decomposition is vital to all mineral
cycles in that nutrients and
minerals are returned to the soil for
use by other organisms
As a result of their decomposing
activities bacteria act as a natural
“maid”, cleaning up after everyone
else
Ecological Impact of Bacteria
Nitrogen makes up 78% of the
atmosphere in the form of N2
In this form nitrogen is unusable to
organisms due to its triple bonding
A large complex of bacteria fix
nitrogen by converting into a form
that can be used by organisms
Ecological Impact of Bacteria
Nitrogen fixing bacteria live in the
soil and in nodules on the roots of
certain types of plants (legumes)
The bacterial complex carries out a
series of reactions that break the
bonds of N2, converting it to nitrates
and nitrites
Ecological Impact of Bacteria
Ecological Impact of Bacteria
Some bacteria negatively impact
their environment by being
pathogenic parasites
Bacterial pathogens cause disease
by secreting toxins that can poison
or destroy cells
Ecological Impact of Bacteria
Bacterial pathogens impact fungi,
plants and animals
Human diseases caused by bacteria
are numerous – typhoid,
pneumonia, cholera, tetenus,
tuberculosis, diptheria, plague,
botulism, gonorrhea, syphilis, etc.
Ecological Impact of Bacteria
Treatment for bacterial infections
can be preventative using vaccines
Post bacterial infection treatment
uses antibiotics
Protista
Large phylum of a variety of different eukaryotic
organisms
Most are unicellular, but a few are multicellular
Cells show distinct intracellular specialization
(division of labor)
Protista
There are a variety of structures used for locomotion:
~ flagella
~ cilia
~ pseudopods
Some groups have no structure for locomotion
Protista
Protists can be grouped into three informal
categories:
~ plant-like (algae)
~ animal-like (protozoans)
fungus-like (slime molds)
~
Protista
Algae occur in many forms and are named according
to their color (green, golden, red & brown)
Most are unicellular, but brown, red and some green
algae are multicellular
Protista
As they are plant-like, algae are autotrophs,
producing their own food by way of photosynthesis
Algae are all aquatic and are found in marine and
fresh waters
Protista
Protista
Protozoans are animal-like protists and therefore
heterotrophs
All protozoans are unicellular
Most protozoans will have one of the three types of
locomotive structures, but some have none
Protista
Some are free living, while others are parasites
Protozoans have world wide distribution, including
terrestrial and aquatic environments as well as being
found inside organisms
Protista
Protista
Slime molds are fungus-like protists and therefore
heterotrophs
Like fungi, slime molds are saprophytic, digesting
their food outside their cells
Protista
Slime molds occur as unicellular individuals and in
large masses of individuals
Slime molds are found in terrestrial environments
feeding on organic detritus and other microorganisms
Protista
Protista
Protists increase in number using binary fission
(asexual reproduction)
Protists gain genetic diversity by way of conjugation
Protista
Protists have three major ecological impacts:
+ photosynthesizers
+ pathogens
+ plankton