as revealed in the fossil record
EVOLUTION... is descent with modification
C22 pg 412-422, C23 pg 428-444, C23 pg 445-458, C25 pg 464-473
progressive changes in organisms that persist over time
helps explain the great diversity, wide geographical
distribution, adaptations and origins of organisms 24.17
micro-evolution- changes in allele frequency within a species
macro-evolution- new species, new forms replacing old
as revealed in the fossil record
Darwinian (classical) Evolution Theory (24 Nov 1859)
is based upon theory of Natural Selection Origin of Species
only small fraction of progeny of a generation survive
survivors have traits (alleles) promote their survival
survival depends on all genes acting together
Darwinian Natural Selection is defined as :
is a change in allele frequency
from generation to generation,
as influenced by environment
that promotes progeny survival. "Survival of Fittest "
The Darwin Awards - improving the human gene
pool by removing oneself from it.
Synthetic (modern) Evolution Theory...
Darwinian evolution mixed with modern genetic theory
Population - an interbreeding group of individuals
Gene Pool - is sum total of all alleles of all indiv in pop.
Variation - is quasi measure of number of alleles
none = only 1 allelic form present
low = few alleles in population differ
high = high heterozygosity, every allele
differs
Adaptation - establishment of organism in particular environment
due to its allelic combinations,
that promotes its survival &
reproduction
Fitness - is reproductive success of one genotype over another genotype
Change in gene pool ....... leads to
better fitness ....... which leads to
adaptation ....... which leads to
reproductive success
Evolution - better adapted genes leaving more progeny
what we need is a way to measure changes in the gene pool.
population genetics
Hardy-Weinberg Equilibrium
1908 G.H.Hardy, English mathematician
& G.Weinberg, German physician
Law of Genetic Equilibrium
describes the gene pool (i.e., all the alleles present) mathematically
defines the ideal case of a NON-evolving populations
for an ideal case... a number of criteria must be met...
- must be an infinitely large populations (large sample sizes)
- should exhibit random mating
- absence of forces which can change allele frequencies
no migration (in/out)
no mutation
no selection
each allele is equally viable (no lethals)
HW law states -->
original percentage of a genotypes alleles remains
constant
HW can be defined algebraically, by the binomial expansion
any gene with 2 allelic forms.... A
and a
let frequency of one allele (A)
= p
& frequency of other allele (a) =
q
then by definition, p + q = 1
HW equation... (p + q)2 = p2
+ 2 pq + q2 = 1
GG Gg gg
| In population of canettes | Orange is dominant (GG) to Green (gg) |
|
|
 |
of 1000 canettes, we observe that...
40 are Green (gg) &
thus 960 are Orange (GG or Gg)
q2 = freq homozygous recessive (green
gg) = 0.04
40/1000 = [0.04] x 1000 =
40
q = freq of recessive allele sq.root of 0.04
= 0.20
p = freq dominant allele [G] = 1 - q = 1 - 0.2
= 0.80
2pq = freq of heterozygote [Gg]
= 2 (0.2) (0.8) = [0.32 x 1000] = 320
p2 = freq of homozygous dominant
= (0.8)2 = [0.64 x 1000] =
640
(23.3)
cf
agents of evolution...
But..... Allele frequencies do change over time via....
Mutation... 1/10,000, random, non-directional
Gene Flow... migration of breeders... in/out
Genetic Drift... random loss of alleles - due to failed matings (23.4)
in very small populations, it's a statistical anomaly
can lead to
fixation or deletion of alleles
Bottleneck Effect... natural disasters leave survivors
which are not representative of whole population
(23.5)
Non-Random Mating... in-breeding lessens heterozygosity...
Founder's Principle... little dispersal -
new allele predominates - small human tribes
Selection... better fit individuals are better reproducers
Artificial - animal husbandry selects best -
mustards- (22.6)
Natural - acts on individuals of populations
factors that may affect selection...
ABIOTIC - non-living factors
temp, humidity, presence heavy metals, Chernobyl
BIOTIC - living factors
predators, parasites, population density, growth rates
Types of Selection (23.11)
STABILIZING - limits extremes of population
one optimum phenotype -
ex: human birth weight
DIRECTIONAL- one best phenotype, not the mean
gradual replacement one by another
DIVERSIFYING (disruptive)- increases the fitness of extremes
no optimum phenotype (2 or more)
-
patchy environments
ex: sexual dimorphism
How do you win the game of evolution:
the mother of all bumper stickers......
the one who leaves behind the best fit genes, wins...
How species form
MICROEVOLUTION
----> MACROEVOLUTION
Definition of a SPECIES (latin - meaning KIND) table 24.1 p 450
morphospecies - most common definition -
different species look different from each other
geographical species - occur in particular places (habitat)
reproductive species - group of actual/potential interbreeding
natural populations, which are reproductively isolated
from other
such groups (can't form hybrids)....
i.e., all individuals which can interbreed &
produce progeny
ex: all dogs, all pigeons
BEST definition...
a group of organisms, which does not interbreed with
others groups and is thus reproductively isolated from
other such groups...
Speciation via reproductive isolation
SPECIATION occurs when a gene pool splits & becomes
reproductively isolated...
i.e., selection favors one allele over another
Some Evolutionary barriers to forming hybrids which can
lead to REPRODUCTIVE ISOLATION (speciation)
1. Pre-Zygotic - prevent mating &/or fertilization 24.5
Geographical isolation ....English oak & California oak (deer mice- 24.6)
Ecological (habitat) isolation..........Tiglons & Ligers
Temporal isolation..........different breeding seasons
Behavorial isolation.........distinct mating rituals
Mechanical isolation........structural differences
2. Post-Zygotic - no development of fertile adults
horse + donkey = mule (sterile chromosome mismatches) see 24.4
Some Evidences microevolution might lead to macroevolution
- all are adaptations via Natural Selection
changes in allele frequency, which altered makeup of a
population..... making some of it better adapted to its environment
1 - Poecilla reticulata (pg 15-17) - guppies in Trinidad pools (web)
predation by... killifish favored survival of LARGER indivduals at maturity
pike-cichlids favored
survival of SMALLER fish at maturity
2- Industrial Melanism & Peppered moth ... H.B.D. Kettlewell
Biston betularia of England
in original butterfly population most had light colored wings
 |
 |
late 1800's- dark winged form increases in freq in populations
esp. in industrialized areas... to almost 100%
light form was preyed upon when on soot blackened trees
dark form not preyed upon... thus an increase in dark's frequency
changed populations allele frequencies via
predation
ex: #3.... Darwin's Finches
there are 13 species of Galopagos Island finches
main difference among brids is structure of their beaks -
an adaptation to their specifc diets (25.7)
seed eaters, cactus eaters, insect eaters, fruit eaters
medium ground finch's beak - 22.7 p422 (408)
eats mostly small (easier to crush) seeds
wet years = lots small seed = beak has
smaller avg depth of beak
dry years = few small seed.... mostly larger seed
= greater avg depth (top to bottom) of beaks
birds w stronger beaks can eat large seed
advantage for "deep beak alleles" during drought years
can reproduce greater number of offspring to survive
Some types or patterns of speciation...
ALLOPATRIC SPECIATION (see fig 24.7)
the initial block to GENE FLOW is GEOGRAPHIC
mts, glaicers, land bridges, land locked lakes, followed by micro-evolution
SYMPATRIC SPECIATION
a subpopulation becomes reproductively isolated in the
midst of the parental population. ex: autopolyploidy - doubling of chrm #'s
ADAPTIVE RADIATION (24.9)
is the emergence of "new" species from single common
ancestor that spreads out to new environments
best example: Darwin's Finches of Galopogos Islands.
ANAGENESIS (phyletic evolution is static)
is the transformation of a single unbranched line of
organisms toward a "new" species.
(24.1)
CLADOGENESIS (branching evolution - diversifying)
budding off of a "new" species from a parent that
continues; favors biological diversity & increases total
# of species.
the rates of evolution ???
is it SLOW & CONSTANT ?
or does it occur in
rapid SPURTS?
GRADUALISM (24.13)
suggests a very slow constant rate...
26.3
periods of stasis, which lack significant evolution change
ex: Lung fishes...
have not
changes in 150 mil yr
PUNCTUATED EQUILIBRIUM
suggests rapid significant changes in a short period
followed by a stable and constant rate of change
[any advantageous role for intron & exons?]
The Cambrian Explosion... tbl 5.1 pg 467
a period of geological time [from roughly 543 mya to 490 mya]
marking the emergence of (sea) ANIMAL life
see great diversity of fossilized animals absent
in late Precambrian
an adaptive radiation due to (?) unique circumstances
(?)
most
extraordinary biological event on our planet
by 505 mya... majority of all animal phyla (between 28-40) had appeared
all basic animal
body plans had been established
Possible causes of rapid evolution of animal life in Cambrian Explosion...
1. O2 levels reached some critical value - favored oxidative metabolism
favored biochemical evolution allowing making of hard
skeletons
2. large amounts of nutrients became available
phosphorites, nitrates, & Fe (via deep
sea upswellings)
3. temperatures become moderate
4. continental drift (which lasted 10-15 my) was occurring at this time
Is there animal life elsewhere in the Universe or is it a "Rare Earth"?
end
Cystic Fibrosis (cc)
is a recessive GENETIC DISEASE of childhood that is characterized by
respiratory & digestive problems and is usually fatal. The average life span of
its victims is only about
24 years.
Effects include heavy production of thick mucus in respiratory
tracts, which increases
susceptibility to respiratory infections; 90 percent of all patients die of chronic lung disease.
Secretions that block pancreatic ducts cause important digestive enzymes to fail to reach the
small intestine. Treatment is directed toward relief of symptoms, and no cure is yet known.
Cystic fibrosis apparently is caused by the inability of
chloride ions to cross the specialized
epithelial cells of salivary, mucus, and sweat glands and the pancreas. The ductal systems become clogged with thick secretions. Cystic fibrosis is a recessive condition from a mutation to a single gene, which produces a disfunctional chloride channel
protein.
Gene lies on Chromosome 7
CFTR gene : cystic fibrosis transmembrane conductance regulator
mutation: ΔF508 ; deletion of 3 nucelotides at positions 507-508 in the CFTR
protein
|
A T ISOLEUCINE 506 C |
|
|
A T ISOLEUCINE 507 C ---> ISOLEUCINE 507 |
|
|
T T PHENYLALANINE 508 --> NO 508 T |
|
|
G G GLYCINE 509 T |
|
|
G T VALINE 510 T |
The disease is a commonly inherited disease among Caucasians;
1/2,500 whites have the disease cc (0.0004 %)
How many carriers Cc are there is U.S. population?
frequency of cc is 0.0004% thus
freq of "c" is sq.root = 0.02%
if freq of c = 0.02 then freq of C = 1 - 0.02 = 0.98%
then freq of 2(Cc) = 2 (.98) (.02) = 0.039%
4% of American whites are asymptomatic carriers
4 out of 100 whites are carriers (Cc)
1 out of 25 in U.S. Caucasian population
end
