EVOLUTION
ORIGIN OF LIFE
Screen Notes-
[additional notes are available on the website (http://over.to/gottfried) or by arrangement, can be copied at lunch time or after school]
Biogenesis versus spontaneous generation
Redi's experiments on the generation of maggots
Spallanzani's experiments on microorganisms and the "vital" force
Pasteur's experiment disproving spontaneous generation
Earth History
Sun-5 billion years old
Earth >4 billion years old
Radioactive dating
half life
Organic compounds
Oparin
Miller & Urey
amino acids from inorganic chemicals
organic chemicals found in space
Fox-first cell-like structures
microspheres, coacervates (droplets)
Replicator...
RNA; DNA
DNA codes for RNA
RNA codes for protein
original world may have not had DNA, only an RNA replicator, where RNA also acted like an enzyme
Heterotroph hypothesis
first cells-heterotrophs taking energy by absorbing pre-formed organic molecules from their environment
archaebacteria
chemosynthesis
photosynthesis and aerobic respiration
3 bya some photosynthetic organisms (cyanobacteria)
First Eukaryotes-endosymbiosis
Fossils
trace of past life
mold, cast, amber, ice, track
law of superposition
relative age versus absolute age
Geologic History (figure page 280)
extinction
mass extinctions
biogeography
Evolutionary Theory....
Evolution-theory that groups of organisms, as species, may
change with passage of time so that descendants differ
morphologically and physiologically from their ancestors.
Evolution is the unifying theme in biology
Evidence:
fossils
biochemical
structural
hand bones
(analogous, homologous)
vestigial organs
1809 Lamark
species evolve from pre- existing species by
1-use and disuse
2-inheritance of acquired characteristics
Darwin 1831 Beagle
(Galapagos, finches)
Lyell-geology
Malthus-overpopulation
1838 - Darwin had the idea
1859 - published (in between-collected additional data, polished writing etc)
1858-Wallace "pushed" Darwin to publish a short paper, followed by
1859-On the Origin of Species by Means of Natural Selection
6 points
1-Overproduction
2-Competition
3-Variation
4-Adaptations
5-Natural Selection
6-Speciation
Proto-Giraffe/Giraffe
Proto-Chicken/Chicken
(in the chicken and the egg question the answer is egg)
Fitness
Where to variations originate?
(DNA)
Some variations not due to heredity
Rate???
Missing links
individuals not species....
Darwin-gradualism
New synthesis of theory includes-
Gould & Eldridge- punctuated equilibria
Synthetic Theory: Evolution occurs at the population level (not the individual level)
-an individual's genes don't change, but the proportions of
particular alleles in a population can
Population genetics and evolution
Population
allele frequency
All plants tall, and
10% heterozygous for Tall
90 % TT
10 % Tt
95 % of genes T
5% of genes t
If in a field of 200 plants there are 30 short, 50 heterozygous and 120 homozygous
120 x TT = 240 T
30 x tt = 60 t
50 x Tt = 50 T and 50 t
totals
290 T
110 t
110/400 = 27.5%
290/400 = 72.5%
Practice...
What are the gene frequencies if...
In a field of 500 pea plants
100 pure tall, 50 hybrid tall and 50 short.
DO IT!
50 x tt = 100 t
50 x Tt = 50 T and 50 t
100 x TT = 200 T
totals
250 T = 62.5%
150 t = 37.5%
All the available genes (alleles) in a population make up a
gene pool
Variations caused by mutation, crossing over, gene recombination, independent assortment, migration
Genetic drift
founder effects
(small populations)
Hardy Weinberg Law
frequencies don't change-populations aren't evolving
genetic equilibria
dominant/recessive has no effect on equilibria unless there is
an effect on fitness
Conditions:
population large
limited or no migration
no mutations
random reproduction
Mathematically if
p = frequency of one allele and (dominant)
q = frequency of the other allele (recessive)
p + q = 1 and
p2 + 2pq + q2 = 1
Do the H-W for the 3 examples of gene frequencies....
What proportion of plants are heterozygous if in a field of 100 plants we find 25 short ones.
We know that
q2 = 20/100
q = 0.45
p = 0.55 (p + q =1)
then
2 p q = .495 = 49.5% heterozygous
TT = 30. 25%
Practice:
In a field 10 of 1000 plants are short. What is the proportion
of genetically pure tall plants (TT).
q2 = 10/1000 = 1%
q = 0.1 p = 0.9
TT = .9 x .9 = .81 = 81%
Tt = 2 x .9 x .1 = .18 =18%
tt = 1%
Adaptations
structural
physiological
camouflage
warning coloration
mimicry
Types of selection
Directional
Stabilizing
Disruptive
Speciation
range
isolation
Convergent Evolution
Co-evolution
Observed Natural Selection
Industrial melanism
Bacterial resistance to antibiotics
-Lederberg experiment-
resistant bacterial clones grow in the presence of antibiotics
-pre-adaptation
Additional Notes.....
Vocabulary:
geologic evolution
organic evolution
fossil
spontaneous generation
heterotroph hypothesis
index fossils
correlation
geologic time scale
homologous
analogous
vestigial
abiogenesis
biogenesis
Evolution
1. A gradual process in which something changes into a
different and usually more complex or better form.
2. Biology.-theory that groups of organisms, as species, may
change with passage of time so that descendants differ
morphologically and physiologically from their ancestors.
Evolution the unifying theme in biology
Over the 4.5 billion year history of the earth the geology has
changed-this is geologic evolution: plate tectonics, mountain
building, erosion etc
Species have changed and evolved over the time life has
existed on earth-organic evolution
Evolution from common ancestors; "bushy" branches
Evidence based in part (not in whole) on fossils-trace or
remains of an organism preserved by natural processes.
MOST animals die and decay and leave no trace.
Occasionally-amber; ice
bones and petrification; teeth; tar; (mineralization)
molds; casts; imprints
Ages of fossils:
sedimentary rock (layered)
date the layers
superposition
(relative dates)
Absolute dating
radioactive decay C-14; U-238;K-40 etc
(igneous/sedimentary problems:
really good "clocks" are in igneous rocks, fossils
are in sedimentary rocks)
Correlation of layers from place to place-discontinuities
index fossils: trilobites; foraminifera
Geologic time scale:
ERA:
Cenozoic
Mesozoic
Paleozoic
Precambrian
Cenozoic
"modern"
65 mya -> now
Tertiary period
65 mya -> 2.5 mya
Quaternary period
2.5 mya -> now
Tertiary = age of Mammals
Quaternary = Age of "humans"
Mesozoic=age of reptiles (Dinosaurs)
225 mya->65 mya
Triassic 225->190
Jurassic 190-136
Cretaceous 136-65
Paleozoic=ages of invertebrates, fishes and amphibians
Earliest period of paleozoic the Cambrian began approximately
570-600 mya
Before the Cambrian, the Precambrian from 3.5 bya to 570 mya
Ages, periods, etc first defined by extinctions
Evolution is not linear-many side branches that "didn't
make it"
Living organisms also indicate evolution
comparative anatomy-structural similarities are evidence for
some evolutionary relationships
whales, bats and humans all have 5 bones in the "hand"
In the whale flipper the 2 bones of the lower arm (ulna and
radius) are larger
These bones are homologous
Similar structures, and embryonic development but different
functions and forms
Bird wing, insect wing, bat wing
analogous structures
similar external forms, but different structures internally
Homology evidence for evolution from common ancestor
Analogy evidence for evolution along different paths
Vestigial structures
no longer useful
reduced in size
evidence of evolution
coccyx-tailbone-reptilian tail
appendix-large digestive sac
Both whales and snakes have vestigial leg bones -4 legged
ancestors
Biochemical similarities-
antibody-antigen reactions
DNA hybridization
Life from non-life; spontaneous generation -abiogenesis-
meat exposed to the air generates maggots
Redi-need flies to get the maggots
Microorganisms-water not sterile
Pasteur-sterilized flasks - isolated air
If all cells come from preexisting cells where did the first
cell come from?
Early earth chemically different from modern earth
Many organic compounds will synthesize from chemicals that
where available in the earth earth's atmosphere or ocean
Aggregates of organics clumped together (clay, bubbles)
The first "organisms" got their energy by using energy in pre-formed compounds
They were heterotrophs
The heterotrophs used up the early chemicals and released CO2
When they ran out of pre-formed compounds-mass extinction-few
with primitive photosynthetic abilities survived
This primitive photosynthetic microbes didn't produce oxygen,
but rather broke apart other organic compounds in photosynthesis
Eventually since producing oxygen from water is more energy
efficient those organisms that did that outgrew their ancestors
Producing oxygen was also a problem.
Oxygen is toxic to most living reactions.
The oxygen first "rusted" all the iron on the
earth's surface
Then as the percentage of oxygen in the air increased the
ozone layer developed, and the high energy environment that first
led to life disappeared.
As more oxygen became available organisms that could not adapt
to it became extinct
This led to the success of heterotrophs that respired oxygen
instead of other chemicals.
Modern Evolutionary Theory
Vocabulary: natural selection; variation; gene pool;
adaptation; population; genetic equilibrium; speciation
Given that organic evolution exists (fossils, biochemical
evidence etc.), what accounts for the origin of and differences
between species.
During the 19th century this was THE question in biology
1809 Jean Baptiste de Lamarck-species not constant, but evolve
from pre-existing species; Changes in species caused by a need to
adapt to the environment
Two principles:
use and disuse (the more you use something the stronger it
gets-and the less you use something the less developed it
becomes)
inheritance of acquired characteristics; Characteristics an
organism develops in its lifetime can be passed on (like wealth)
to offspring
By stretching to reach food giraffe necks got longer. They
passed these long necks to offspring
(1870) Weismann-mice tails cut off for 22 generations- 23rd
generation still had tails.
Cultural evolution may work by Lamarckian means, but not
organic evolution.
Darwin-1831-naturalist on HMS Beagle 5 year expedition; collected specimens, made observations
especially in the Galapagos islands; Finches-
setting the stage - Principles of Geology-Lyell (earth old, gradually changing)
On Darwin's return- Malthus-An Essay on the Principle of Population
(Human population problems go back a long time)
Malthus-population increases geometrically 2 4 8 16 32 64 128
food can at most increase arithmetically 2 3 4 5 6 7 8
Therefore people starve! To balance population growth and food, millions must die by some means
Excess production of people
Darwin- Malthus also applies to organisms who produce more
offspring than could possibly survive (cod-millions of eggs)
1838-idea of "Natural" Selection (as opposed to "Artificial" Selection by breeders)
Darwin spent 20 years collating data, polishing his writing
etc.
1858 Wallace wrote an essay based on studies of beetles in Malaysia that was on Natural Selection
Darwin "co-published" with Wallace and then produced his great work
"On the Origin of Species by Means of Natural
Selection" 1859
six points:
1-Overproduction
2-Competition
3-Variation
4-Adaptations
5-Natural Selection
6-Speciation
Giraffes- many more "proto-giraffes" than environment can support (1)
they must compete for resources (2)
some have longer necks than others (3)
A longer neck allows some proto-giraffes to be better adapted (4)
they then produce more offspring than those with shorter necks (5)
In time they become substantially different from the original
"proto- giraffe" and a giraffe is born (6)
Fitness- production of F2 generation
Flaws-Problems
1-where do variations originate (remember this is 1859)
2-some variations cause by the environment not heredity
3-rate of evolution
4-missing links in fossil record
5-evolution occurs to individuals
Darwinian theory-
gradualism
Gould and Eldridge- punctuated equilibria-evolution in fits
and spurts and environment changes
Synthetic Theory: Evolution occurs at the population level (not the individual level)
-an individual's genes don't change, but the proportions of
particular alleles in a population can
Population=group of organisms of the same species living
together (interbreeding)
Study of changes in allele frequencies in populations=population genetics
Frequencies-number of individuals per hundred who have a
particular allele
In a field of pea plants all the plants are tall.
If 10% of plants are heterozygous for stem length the frequency of the allele for tall is .95 (95%) and for short is .5 (5%)
[In 100 plants there are 200 genes; In 10 of those plants 1 of
the 2 genes for length is the allele for short; therefore 10/200
genes are for short]
In a field of pea plants 5% of the plants are short, 10% are heterozygous for stem length
What are the gene frequencies?
10% short 90% tall
All the available genes (alleles) in a population make up a
gene pool
Genetic Variation (remember-only variation in the gametes
effects evolution)
mutation-(De Vries); gene recombination; crossing over;
independent assortment; Migration
Genetic drift; -small populations; founder effects
Hardy-Weinberg Law
If conditions exist such that frequencies don't change a
population is in genetic equilibrium
Dominant and recessive have no effect on genetic equilibria if
there is no difference in fitness
4 conditions need to be true for H-W to hold true and a
population to be in genetic equilibria
1-Population must be large
2-Migration into or out of the population be limited or random
3-mutations don't occur
4-reproduction must be random (fitness for alleles must be the
same)
These 4 never really exist, but the theory is useful since we
can figure out the rate of evolution from how much a population
varies from H-W
Mathematically if
p = frequency of one allele and
q = frequency of the other allele
p + q = 1 and
p2 + 2pq + q2 = 1
Adaptations:
Structural-body of an organism
Physiological-metabolism of organism
Adaptations for protection- camouflage; warning coloration;
mimicry
Types of Selection
Directional Selection-
an extreme phenotype becomes a favorable adaptation - population evolves
Stabilizing selection -most common-
extreme phenotypes "weeded" out of the population reducing variation in a trait
Disruptive selection (rare)
2 opposite rare phenotypes are favorable, while the average is unfavorable-extremes survive
2 sub-populations
Speciation: range-where you find a species
At far reaches of a range a species may have different gene frequencies
Isolation-geographic leading to reproductive isolation
Reproductive isolation-new species-
different behavior
different time of mating
different structures
infertility
(In plants-polyploidy can produce new species in 1 generation
since the polyploid plant can no longer interbreed with the
parent species)
Adaptive radiation-spreading out into new environments which are different from the original environment w/o large migrations back and forth to mix the gene pool
If the new environment has niches that are open variations
will take advantage of these niches
Darwin's Finches
Convergent Evolution: Some answers to life's problems are better than others
vertebrate and octopus eye have similar structures although they do not share common "eyed" ancestors
bird and insect wings are similar in shape
Tuna, dolphin (Flipper), sharks, and attack submarines share
shape
Co-evolution-
bees and flowers
ants and acacia trees
Observed Natural Selection
Industrial melanism
Bacterial resistance to antibiotics
-Lederberg experiment-
resistant bacterial clones grow in the presence of antibiotics
-pre-adaptation
-Newest information
some bacteria seem to increase the rate at which mutations
occur in specific genes when under stress.
This "directed" evolution runs counter to the
Synthetic Theory of Evolution, since adaptive mutations occur as
a result of selection pressure
Insect resistance to pesticides (DDT)