Upon completion of this unit you will be able to:
1. Define and discuss the gene pool.
2. State the conditions under which
the Hardy-Weinberg Law is applicable.
3. Apply the Hardy-Weinberg Law to the
prediction of the frequency of alleles in a population.
4. Define evolution and explain the
two step process of evolution.
5. Describe and explain with examples
mechanisms that increase genetic variability.
6. Describe and explain using examples
manners in which variability can be reduced.
7. Compare and contrast genetic drift and
the founder effect.
8. Describe how genetic drift and natural
selection can affect gene frequencies in a
population.
9. Define a species.
10. Explain how a species may be seperated
into distinct groups by geographical
isolation, mutation and natural selection.
11. Explain how a subspecies differs from
a species.
12. Describe and give examples of each
of the following prezygotic isolating
mechanisms: Mechanical isolation,
temporal isolation, behavioral isolation,
gamete incompatability and ecological
isolation.
13. Describe and give examples of each
of the following postzygotic isolating
mechanisms: Hybrid inviability, hybrid
infertility and hybrid breakdown.
14. Discuss the competitive exclusion
principle.
15. Provide the definition and examples
of ecological equivalents.
16. Contrast the views of Lamarck with
those of Darwin and Wallace.
17. Relate natural selection to survival
of the fittest.
18. Relate the experiments of Miller in
1953 to the origin of life.
19. List and discuss some examples of present
day evolution.
20. Compare and contrast evolutionary gradualism
and punctuated equilibrium.
21. Provide examples of convergent and
divergent evolution.
22. Define adaptive radiation.
23. Explain how common origin can be established
in various groups of living organisms.
24. Discuss possible reasons for the
extinction of a species.
Unit References:
Text Chapters 12, 13, 14, 19, 20
http://www.mhhe.com/enger12
Unit 9: Adaptation, Speciation and Evolution
Population genetics
(Objective #1) text pgs 240-243
Population- a group of organisms inhabiting
an area. Includes individuals of the same
type that are capable of breeding
and producing viable offspring (human pop.;
ferret pop.; cat pop; etc.)
gene pool- all the genes (alleles) available to a population
Statistical studies- employ known rates to
predict future outcomes. Need large #s to be
most accurate
-studies help determine changes in
population, changes in allele frequency
Hardy-Weinberg Equilibrium
(Objectives #2, 3) Text pgs 273-277
- under certain conditions,
gene frequencies and genotype frequencies
remain the same from one generation to the
next in sexually reproducing animals.
Conditions: 1. no selection
2.
no migration in or out
3.
no mutations, lethals
4.
large population so as not to be affected by random chance.
**if the cross between two heterozygous carriers
of albanism (a) produce 25% albino
offspring, why isn't the population of humans
25% albino? How many heterozygous
carriers are there? Is it likely that two
heterozygotes mate with each other?
Key terms: gene pool, inbreeding, allele frequency, population
Hardy- Weinberg: mathmaticians, endeavored
to link inheritance to predictable
mathematical models.
let p = frequency of dominant allele
let q = frequency of recessive allele
p + q = 1 (or 100%) All individuals have two alleles for any trait, p + q = all alleles in pop
Binomial Expansion- statistical method to fit general population characteristics
(p + q)2 = 1; (p + q) 2 = p2 + 2pq + q2 = 1 *notice 1:2:1 ratio (genotype)
p2 or p X p = frequency of homozygous
dominant
2pq or 2 X p X q = frequency of heterozygotes
q2 or q X q = frequency of homozygous
recessive
Production of variation: frequencies of
genes in the gene pool stay constant unless
change (evolution) occurs
Hardy-Weinberg implies no change, however, Hardy-Weinberg conditions rarely exist
Evolutionary process requires two steps
(Objective #4):
1. Production of genotype and therefore
phenotype variations (adaptations)
2. Sorting out and reduction of variations
passed on to next generation (field test)
**Evolution can be defined as changes in allele frequency within a population over time
Variations Produced by
(Objective #5) text pgs. 243-245:
1. Mutation - 1/100,00 to
1/10,000,000 per generation, likely to be neutral or harmful
(non adaptive).
Replacement of one allele
with another.
2. Gene flow - change of allele
frequency due to migration into or out of a population.
-removing alleles from one
group and introducing them to another
Ex. Africanized Killer bees; Hybrid production; "Melting Pot", introduced species
Check out:
Carl Hayden Bee Research Center
Africanized Honey Bee
3. Recombination - gene mixing during meiosis (sexual reproduction)
4. Non Random mating- sexual selection (Bower birds; Humans- tall X tall etc.) Speciation
Variations Reduced (Objective #6, 7) by:
1. Genetic drift
text pgs. 245-247- movement of genes out of the population (effects
greatest on small pops)
Population bottleneck
- cheetahs, black footed ferret
Just as a small amount
of liquid can get through a narrow neck bottle, only a
small pop may survive a
disaster, leaving depleated gene pool.
Founder effect- a
few individuals separate from a large pop and establish a new one
Amish- recessive alleles
for short forearms and lower legs. As a result, Amish
in Penn. have a freq. for
these alleles of 1/14 whereas other pops have a
freq of 1/1000
Check Out:
Genetic Drift Model
Natural Selection (Objective #8, 17) text pgs 261-265
Adaptations resulting from changes in allele
frequencies due to differential reproduction
and survival
-what do cactuses, brown stone plants,
poison ivy and Thompson's gazelles have in common
"Survival of the Fittest"- surviving
to reproductive age and pass favorable genes on to the
next generation, favorable genes enhance
survival, therefore, survivors leave more offspring
and favorable genes are passed on.
-natural selection chooses parents with most suitable phenotypes (coded by genotypes)
Result: Adaptations- accumulation
of structural, physiological or behavioral traits that
increase an organisms fitness.
(peppered moth, insecticide resistance)
Check Out: The Peppered Moth Model
Maintaining Variation- Speciation
(Objective #9) pgs 282-287
Species- group of organisms
that interbreed naturally to produce fertile offspring
Speciation- portion of gene pool becomes isolated; process of generating new species
*Accumulation of changes may seperate
a population into distinct groups (Objective #10)
Speciation: three step process
1. Geographic isolation-
prevents free flow of genes
2. Selection- field test
determines which genetic combos are valuable (selection
pressure)
3. Accumulation of genetic
differences and time to develop differences
sufficient to prevent
reproduction
Examples: Tassel eared squirrels, snails (pg 241)
?What if after a period of time
the barriers are removed?
-pops interact but no gene
flow: different mutations
different adaptations
different gene recombinations
Subspecies (races)
(Objective #11)- groups significantly different in appearance
behavior and physiology
but may interbreed
-geographic variants
differ but DNA changes not dramatic enoughto prevent
interbreeding
Check Out:
Twenty-one Species That
Were One
Observed Instances of Speciation
Maintaining Genetic (Reproductive) Isolation
(Objective #12) text
pgs 285-287 - reproductive isolating
mechanisms
-prevent cross-species mating (why
can't a dog and a cat have an offspring together?
Check Out:
PBS- Isolating Mechanisms: Lacewing Songs
1. Prezygotic
(Objective #12)- prevent mating or fertilization
a. Habitat Preference (Ecological
isolation)
-pops in different habitats do
not meet (garter snakes, parasites, Mexico
Towhee's)
b. Temporal Isolation- mating
or flowering occur at different seasons or times of day
-Brown Trout, fall; Rainbow
Trout, spring
c. Behavioral Isolation-
little or no sexual attraction between males and females
-fireflies (blinking); insects
(pheromones); meadowlarks (song)
d. Mechanical Isolation- structural differences in genetalia (dragon flies)
e. Gametic Isolation- male
and female gametes fail to attract each other or are
inviable (gametic recognition) dog
X cat ---> NOT!!
2. Postzygotic
(Objective #13)- prevent development of viable, fertile adult
a. Hybrid Inviability - hybrid
zygotes fail to develop or fail to reach reproductive
maturity
b. Hybrid sterility- hybrids
fail to produce functional gametes; mules (failure of
meiosis)
c. Hybrid breakdown- offspring
of hybrids have reduced viability or fertility
-Cotton, radish/cabbage; usually
hybrids have to give up something
Development of Evolutionary Thought/ Origin of Species text pgs 260-263, chapter 20
Check out:
History of Evolutionary Thought
Evolution (Objective
#4)- Genetic and phenotypic changes occurring in a pop. over
time,
resulting in increased
adaptations of organisms to the prevailing environment.
Species- group of reproductively isolated individuals or populations
George Cuvier- Catastrophism
Charles Lyall- geologic changes slow,
therefore, earth old
Thomas Malthus- death and famine
are inevitable because human pops. tend to
increase faster than the supply
of food. Necessitates struggle to survive.
Lamark (1744-1829)- Inheritance of
Acquired Characteristics (Objective #16)
"Changes in individual body over
its life could be passed to offspring"
-believed evolution responded
to "felt needs"
2 principles: 1. use
and disuse
2. Inheritance of acquired characteristics
Giraffes neck; blacksmith's sons
**wrong mechanism of change:
Muscle cell enlargement due to lifting
weights has no effect
on gene for muscle development
Darwin/ Wallace (~1869)- Natural Selection;
"Survival of the Fittest" (Objective #16)
-all species have great biotic
potential
-no two organisms are alike, variations occur constantly, at random
-natural resources are limited
-individuals with advantageous variations most likely to survive (acquire resource)
-individuals best suited to survive will be best suited to leave most offspring.
-genes of individuals producing
most offspring will be found most frequently in
future generations
**Darwin, Wallace, Lamarck had no knowledge of Mendel
Natural Selection
(Objective #14, 15, 17)- guiding force of evolution, environmental
selection of individuals that are
well adapted to their environment and fit
to reproduce.
Competitive Exclusion Principle-
two species, same environmental requirements, cannot
live together; competition forces one to
leave, adapt differently or become extinct
ecological equivalents- organisms
performing similar activities in widely seperated
biomes (kangaroo/antelope)
Artificial Selection- outside forces guiding selection of desired traits
Check out : Ascent of the Dog
Evolutionary Applications
(Objective #19, 20, 21, 22)
text pgs. 287-291
1. Convergent Evolution- different
organisms similar due to common environment
Ex. water ---> seals, penguins,
turtles
2. Divergent Evolution- speciation
events cause many branches in evolution of group
-Adaptive Radiation- Darwins
Finches (competitive exclusion ---> adaptation
---> speciation)
3. Coevolution- bee pollinated flowers; parasites; disease
Chemical Evolution (Objective #18) - Could this have all begun from scratch?
Stanley Miller 1953
Primitive Atmosphere- NH3, H2, H2O
vapor, CH4 --> electrical charge -->Amino Acids
purines
pyrimidines
Chemical evolution of life- primordial
soup
Simple molecules + Simple molecules
---> complex molecules (carbo, fat, protein, etc)
Extinction (Objective
#26) text pg 288 - 99%+ of species
that have existed, exist no more (baseball)
-changing environments, unable
to adapt
-Dinosaurs, asteroid/volcanoes
Habitat Destruction - animals
forced to leave habitat, are unable to adapt or compete
in new one
Isolation - line dies out because
gene pool not diverse. Not enough individuals to
maintain hybrid vigor (black footed
ferret, virtually all endangered species)
Specialization - yucca moth is only pollinator of yucca plant. Moth dies . . . .
Check Out : The Extinction files