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BIG Idea I
The process of evolution drives the diversity and unity of life
EVOLUTION is a change in the genetic makeup of a population over time
1.A.1 Natural Selection is a major mechanism of evolution
a. Darwin’s theory
- populations produce more offspring than can survive
- inheritable variations occur individuals in a population
- resources are limited so there is competition
- individuals with more favorable variations or phenotypes are
more likely to survive and produce more offspring
- traits are passed to next generation (through their genes)
Remember: it’s the environment that “selects” for or against the individuals
Remember: natural selection acts on the PHENOTYPE
(recall tho – phenotype is determined by genotype)
Remember: natural selection is the only force that makes a population better
“fit” to its environment
Remember: Environments change – so what genes are selected “for” in one
environment may be selected “against” if environments change (e.g.
global warming (fur coats not a needed adaptation in warm temps)
h. mathematical approaches are used to calculate changes in allele
frequency, providing evidence for the occurrence of
evolution in a population.
Remember : H-W says that populations are NOT evolving, if you find that the
allele frequencies change (e.g. p= .2 in year one and then .7 in year
10) then you have evidence that the population IS evolving!
Be able to analyze graphical analysis of allele frequencies:
Be able to apply the H-W equation
b. Evolutionary fitness is measured by reproductive success
Remember: Evolutionary fitness is the amount of genes that are passed on to
next generation – more offspring  more genes!
Remember: Evolution is defined as “differential reproductive success”
c. Genetic variation and mutation play roles in natural selection.
A diverse gene pool is important for the survival of a species in a
changing environment.
- Heterozygosity is “good” for populations – allows population to
respond to a changing environment. If too many alleles are “fixed”
populations may go extinct.
Remember: as environments change populations may have to respond to
different selective pressures – so having diversity makes the
population flexible.
d. Environments can be more or less stable or fluctuating, and this
affects evolutionary rate and direction; different genetic
variations can be selected in each generation.
- stable environments – rates are slower, unstable – faster
e. An adaptation is a genetic variation that is favored by selection
and is manifested as a trait that provides an advantage to an
organism in a particular environment.
1.A.2 Natural Selection acts on phenotypic variations in populations
a. environments change and act as selective mechanism on
populations
·flowering time in relation to global climate change
Plants are flowering
earlier as temps
get warmer
Remember: organisms don’t “adapt” (this is always murky water!) – organisms
are born with variations and variations are “selected” by the
environment.
Remember: Lemark said giraffe’s adapt by stretching their necks (this is the
theory of acquired characteristics and is a BIG no no in evolutionary
terms! Don’t use this – be careful of your language!)
f. In addition to natural selection, chance and random events can
influence the evolutionary process, especially for small
populations
·peppered moth (directional selection)
Remember: Population lab – Genetic drift (chance events) can move populations
towards one allele or the other – this is not natural selection and
can’t be predicted or controlled
-Two types of Genetic drift (Bottlenecks and Founder Effect)
Both are situations where new populations may not resemble original
population s
Both occur when there is a drastic reduction in the gene pool
Bottleneck – Prairie Chicken loss of range= loss of genetic diversity
Founder – Amish - Ellis-van Creveld syndrome – polydactyly
g. 5 Conditions for a population or an allele to be in Hard-Weinberg
equilibrium: 1. Large population size
2. no Gene Flow (immigration or emigration)
3. no mutations
4. random mating
5. no natural selection
Remember: H-W equations: p2 + 2pq + q2 = 1 and p + q = 1
Always start with finding the % of the recessives (that’s q2 )!
Take the square root of q2 and you’ll have q
Subtract q from 1 and you have p. Plug them into the equation
p2 = homozygous dominants (AA) 2pq = heterozygotes (Aa)
b. Phenotypic variations are not directed by the environment but
occur through RANDOM changes in the DNA and through
new gene combinations.
Remember: natural selection is only an “editing” mechanism, it cannot CREATE
new genes – only mutation can do that
Remember: organisms cannot change their genes- they have what they were
born with. e.g. Organisms cannot “evolve” a new body color.
Remember: new gene combinations arise through MEIOSIS –
1. crossing over 2. Independent assortment 3. Random fertilization
Artificial selection: (wild mustard)
Selective pressures can cause populations to change
c. some phenotypic variations significantly increase or decrease
fitness of the organism and the population
Loss of genetic diversity within a crop species:
- diversity allows for some members to survive
- monocrops (all one crop) is disasterous if disease strikes
·sickle cell anemia ( fitness (except in areas where malaria is present)
·peppered moth
·DDT resistance in insects
Overuse of antibiotics:
Remember: insects are not developing resistance – a small number are born
with a variation to be resistant. When DDT is sprayed, it kills all the
non-resistant insects leaving only resistant ones. They mate and
soon the entire population is resistant to the pesticide.
Also – insects don’t have an immune system (remember TOLL like receptors?)
Remember: The DDT is selecting which organism will live
Remember: this also is true of antibiotic – resistance in bacteria
1.A.3: Evolutionary change is also driven by random processes
a. Genetic drift is a nonselective process occurring in small pop’s
This is a BIG BiG problem that CB wants you to remember!
d. Humans impact variation in other species
·artificial selection
·Loss of genetic diversity within a crop species
·overuse of antibiotics (see above)
b. reduction of genetic variation within a given population can
increase the differences between populations of the same species
1.A.4: Biological evolution is supported by scientific evidence from
many disciplines, including mathematics
a. scientific evidence of biological evolution uses information from
geographical (biogeography), geological (fossils), physical
(comparative anatomy), chemical (DNA, RNA, protein analysis) and
mathematical applications.
Carbon-14 dating
Relationship within phylogenetic trees
2. Morphological homologies represent features shared by common
ancestry. Vestigial structures are remnants of functional structures,
which can be compared to fossils and provide evidence for
evolution.
Remember: Homologous structures come from common ancestry and are
representative of DIVERGENT evolution
b. molecular, morphological and genetic information of existing and
extinct organisms add to our understanding of evolution. (know each
of these)
·1. Fossils can be dated by a variety of methods that provide evidence for
evolution. These include the age of the rocks where a fossil is found (RELATIVE
DATING), the rate of decay of isotopes including carbon-14, the relationships
within phylogenetic trees, and the mathematical calculations that take into
account information from chemical properties and/or geographical data.
Relative dating: (correlation to infer the relative age of rocks & fossils)
Remember: Analogous structures do not come from common ancestry – but
rather evolutionary pressures. They are representative of
CONVERGENT evolution
Vestigial structures:
2. Major features of the genetic code are shared by all modern living
systems
3. Metabolic pathways are conserved across all currently recognized
domains
b. Structural evidence supports the relatedness of all eukaryotes
·cytoskeleton
·membrane-bound organelles (mitochondria and/or chloroplasts)
·linear chromosomes
·endomembrane systems, including the nuclear envelope
3. Biochemical and genetic similarities, in particular DNA nucleotide and
protein sequences, provide evidence for evolution and ancestry.
4. Mathematical models and simulations can be used to illustrate and support
evolutionary concepts
· graphical analyses of allele frequencies in a population
· analysis of sequence data sets
· analysis of phylogenetic trees
· construction of phylogenetic trees based on sequence data
1.B.2: Phylogenetic trees and cladograms are graphical representations
(models) of evolutionary history that can be tested.
a. Phylogenetic trees and cladograms can represent traits that are either
derived or lost due to evolution
1B: Organisms are linked by lines of descent from common ancestry
1.B.1: Organisms share many conserved core processes and features
that evolved and are widely distributed among organisms today.
a. structural and functional evidence supports the relatedness of all
domains
1. DNA and RNA are carriers of genetic information through
transcription, translation and replication
·number of heart chambers in animals
· opposable thumbs
· absence of legs in some sea mammals
b. Phylogenetic trees and cladograms illustrate speciation that has occurred,
in that relatedness of any two groups on the tree is shown by how recently
two groups had a common ancestor
c. Phylogenetic trees and cladograms can be constructed from morphological
similarities of living or fossil species, and from DNA and protein sequence
similarities, by employing computer programs that have sophisticated ways of
measuring relatedness among organisms (BLAST lab!)
d. Phylogenetic trees are dynamic (constantly being revised), based on the
biological data used, new mathematical and computational ideas and current
and emerging knowledge.
1 C: Life continues to evolve within a changing environment
1.C.1 speciation and extinction have occurred throughout the Earth’s
history.
a. speciation rates can vary, especially when adaptive radiation
occurs when new habitats become available.
b. New species arise from reproductive isolation over time, which can involve
scales of hundreds of thousands or even millions of years, or speciation can
occur rapidly through mechanisms such as polyploidy in plants.
- SYMPATRIC SPECIATION
·autopolyploidy, allopolyploidy
b. species extinction rates are rapid at times of ecological stress
· 5 Major extinctions on Earth
1.C.3 Populations of organisms continue to evolve
a. scientific evidence supports the idea that evolution has occurred in
all species
b. scientific evidence supports the idea that evolution continues to
occur
·chemical resistance (mutations for resistance to antibiotics, pesticides,
herbicides or chemotherapy drugs occur in the absence of the
chemical)
· Human impact on ecosystems and species extinction rates
(refer to your Darwin200 Evo packet reading)
1.C.2: speciation may occur when two populations become
reproductively isolated from one another
a. speciation results in diversity of life forms. Species can be physically
separated by a geographic barrier (allopatric speciation) such as an
ocean or a mountain range, or various pre-zygotic and post-zygotic
mechanisms can maintain reproductive isolation and prevent gene
flow.
Remember: the key to maintaining a species is Reproductive Isolation
Remember: species definition: members of a population that are capable of
interbreeding and producing viable (fertile) offspring.
·emergent diseases
· observed directional phenotypic change in a population (Grant’s
observations of Darwin’s finches in the Galapagos (this was in your
Darwin200 reading!))
·a Eukaryotic example that describes evolution of a structure or process
such as heart chambers, limbs, the brain and the immune system
1D: The origin of living systems is explained by natural processes
1.D.1: There are several hypotheses about the natural origin of life on
Earth, each with supporting scientific evidence.
a. scientific evidence supports the various models
- know EACH of the following;
·1. Primitive Earth provided inorganic precursors from which organic
molecules could have been synthesized due to the presence of available free
energy and the absence of a significant quantity of oxygen.
·2. In turn these molecules served as monomers or building blocks for the
formation of more complex molecules, including amino acids and nucleotides.
·3. The joining of these monomers produced polymers with the ability to
replicate, store and transfer information.
·4. These complex reaction sets could have occurred in solutions (organic
soup model) or as reactions on solid reactive surfaces.
·5. The RNA World hypothesis proposes that RNA (not DNA) could have
been the earliest genetic material.
Urey- Miller experiment:
b. Molecular and genetic evidence from extant (living) and extinct
organisms indicates that all organisms on Earth share a common
ancestral origin of life.
- understand EACH of the following:
1. scientific evidence includes molecular building blocks that are
common to all life forms.
2. Scientific evidence includes a common genetic code.
RNA World Hypothesis:
1.D.2: Scientific evidence from many different disciplines supports
models of the origin of life.
a. Geological evidence provides support for models of the origin of
life on Earth
- understand EACH of the following:
1. The earth formed approximately 4.6 billion years ago (bya) and
the environment was too hostile for life until 3.9 bya, while the
earliest fossil evidence for life dates to 3.5 bya. Taken together, this
evidence provides a plausible range of dates when the origin of life
could have occurred.
2. Chemical experiments have shown that it is possible to form
complex organic molecules in the absence of life. (Urey-Miller!)