Evolution Flashcards
Evolution
- is the gradual development and
change of heritable traits (allele frequencies) in
populations over successive generations.
Evolution increases biodiversity.
Evidence of Evolution include
1) Paleontology
2) Biogeographic
3) embryology
4) Comparative Anatomy
5) Biochemical
Evidence of Evolution: Paleontology
- is the study of fossils through actual remains of the animal or their traces
(ichnofossils). Petrification is the process by which living organisms turn into fossils. These fossils allow us to see the development of species through time by comparing deepest (oldest) fossils to shallowest (youngest).
Evidence of Evolution: Biogeographic
- biogeographic evidence, we can
see the spread of different species around
the world and analyze similarities and
differences.
Evidence of Evolution: embryology
- allows us to see embryological
similarities and differences between early
stages of related organisms. Eg. all chordates
have a gill slit during development.
Evidence of Evolution: Comparative Anatomy
- compares different body parts of different animals. Includes: 1) homologous structure, 2) analogous structure, and 3) vestigial structure
Evidence of Evolution: Biochemical
- allow for DNA sequence comparisons. Can see conserved
DNA sequences (higher similarity = higher relatedness) and common conserved pathways (eg. Krebs cycle). .
Homologous structures
- may or may not perform the same function but have a
common ancestor. eg. forearm of bird and
forearm of human.
Analogous structures:
- same function, do not have a common ancestor. eg. bird
wings and bat wings.
Vestigial structures:
- serve no purpose but are homologous to functional structures in other organisms eg. human appendix and cow cecum.
Theory of evolution
1) Cuvier’s catastrophism
2) Lamark’s inheritance of acquired traits
3) Darwin’s Natural Selection
Cuvier’s catastrophism
- lead to mass extinctions of species in those areas. The different
populations in different areas were shaped by what catastrophes had occurred, and what random organisms then survived and populated that area.
Lamark’s inheritance of acquired traits
● Use and disuse: used body parts will develop and unused ones are weakened, leading to evolution.
● Inheritance of acquired traits: traits acquired through use and disuse are
passed onto offspring (eg. giraffe stretching neck will cause its neck to
develop, and produce long necked offspring). This is incorrect - acquired
characteristics are generally not heritable.
Darwin - Theory of Natural Selection.
- is the gradual, non-random process where allele frequencies change as a
result of environmental interaction. Survival of the fittest occurs as individuals with greatest fitness (ability to survive and produce viable and fertile offspring) have greatest success, and pass on more DNA to future generations compared to less fit parents. Leads to the evolution of the population (not individuals).
Requirements for Natural Selection
1) Demand > supply
2) Difference in level of fitness
3) Variations in traits due to genetic influence
4) variation in traits due to reproduction and/or survival
Requirements for Natural Selection: Demand > supply
- results in competition for survival (fittest
survive to pass on genes).
Requirements for Natural Selection: Difference in level of fitness
- differentiate ability to compete and
survive (eg. black peppered moths favored
over white moths during Industrial
Revolution).
Requirements for Natural Selection: Variations in traits due to genetic influence
- Variation in traits must be genetically-influenced (heritable) to be passed onto offspring.
Requirements for Natural Selection: variation in traits due to reproduction and/or survival
- Variation in traits must be significant for
reproduction and/or survival: genes
improving reproductive success/survival are
favored and increase over generations and
vice versa.
Types of Natural Selection include:
1) Stabilizing Selection
2) Directional Selection
3) Disruptive Selection
Stabilizing Selection
- mainstream (average) is favored (eg. birth weight). Diagram follows
a standard bell curve.
Directional Selection
- one extreme favored (eg. longest giraffe neck allows access to the
most leaves).
Disruptive Selection
- : rare traits favored, mainstream is not. (eg. snails living in low
and high vegetation areas).
Other types of Selection
1) Sexual Selection
2) Artificial Selection
Sexual Selection
- non-random mating between males and females. Females favor high quality partners, males prefer high quantity of partners to increase their number of offspring. Traits selected for may be favorable for reproduction
but not for survival.
Artificial Selection
- carried out by humans to selectively breed for specific traits (eg. dog
breeding).
Gene Equilibrium: No evolution
- The Hardy-Weinberg formula calculates genetic
frequency during genetic equilibrium (no
change in gene frequencies). If both equations
hold true, the population is under
Hardy-Weinberg equilibrium.
p+q = 1
P^2 + 2pq + q^2 = 1
p= freq. of dominant allele
q= freq. of recessive allele
P^2 = freq of homozygous dominant
2pq = freq of heterozygous
q^2 = freq of homozygous recessive
The requirements for Hardy-Weinberg
equilibrium are:
- (Mnemonic: Large, Random, M&M)
● Large population: minimizes genetic drift.
● Random mating
● No mutation
● No natural selection
● No migration (gene flow): population must
be isolated.
When conditions are not met, evolution occurs.
Microevolution
- is the process when gene
frequencies change within a population over
generations (favorable genes increase,
unfavorable decrease).
Factors causing Microevolution:
1) Genetic drift
2) non-random mating
3) mutations
4) natural selection
5) gene flow
Microevolution: Genetic Drift
- allele frequencies change by chance. Larger effects on small populations. Includes: 1) Bottleneck effect and 2) founder effect
● Bottleneck effect
- smaller gene pool, some alleles may be lost (eg. disaster
killing majority of population).
● Founder effect
- some individuals migrate away from the population.
Microevolution: Non-random Mating
- sexual selection, outbreeding, inbreeding.
Microevolution: Mutations
- can be dormant until environmental change allows it to flourish.
Microevolution: Natural Selection
- no luck involved
Microevolution: Gene Flow
- migration (non-random) moving
alleles between populations, leading to
variation through mixing.
Sources of Gene Variation
1) Mutation
2) sexual reproduction
3) balanced polymorphism
4) polyploidy
Sources of Gene Variation: Mutation
- must not be fatal.
Sources of Gene Variation: Sexual reproduction
- crossing over, independent assortment and random joining
of gametes.
Sources of Gene Variation: balanced polymorphism
- maintains a variety of phenotypes within a population. Includes:
1) Heterozygote advantage,
2) Minority advantage,
3) neutral variations
Sources of Gene Variation: Polyploidy
Heterozygote advantage
- (eg. sickle cell anemia). Two parents produce an offspring that is more fit than either parent.
Minority Advantage
- : rare phenotypes offer higher fitness. Cycle between high and low frequency. (eg. advantageous against hunters’ search images).
Neutral Variations
- may become beneficial if the environment changes.
Polyploidy
- : plants have multiple copies of
alleles introducing more variety and
preserving different alleles. Can also mask
effects of a harmful recessive allele.
Macroevolution
- is long-term and occurs at a
level at or higher than species. Species are
reproductively isolated (via prezygotic and
postzygotic isolating mechanisms) resulting in a
lack of gene flow between species.
includes:
1) prezygotic isolation
2) postzygotic isolation
prezygotic isolation
- mechanisms are barriers that prevent fertilization and zygote
formation from occurring between species. - includes:
1) habitat isolation
2) temporal isolation
3) behavioral isolation
4) mechanical isolation
5) gamete isolation (incompatibility)
Habitat Isolation:
- occupying different habitats.
Temporal Isolation
- reproducing at different times/seasons.
Behavioral Isolation
- different courtship rituals.
Mechanical Isolation
- male and female
genitalia are not compatible.
Gamete Isolation (Incompatibility):
- gametes do not recognize or are unable
to fertilize each other.
Postzygotic Isolation
- refers to barriers to organism success after zygote has formed.
- includes:
1) hybrid mortality (inviability)
2) hybrid sterility
3) hybrid F2 breakdown
hybrid mortality (inviability)
- hybrid zygote not-viable and does not survive past embryonic stage (often due to different chromosome numbers).
Hybrid Sterility
- hybrid zygote sterile (infertile).
Hybrid F2 Breakdown:
-Hybrid F2 generation have reduced fitness
compared to their parental generation.
Speciation
- is how species form, starting with
reproductive isolation, which leads to
interruption of gene flow between populations
that gradually develop into two species. - includes:
1) allopatric speciation
2) sympatric speciation
Allopatric Speciation:
- occurs due to a geographical barrier.
- e.g: Adaptive radiation
adaptive Radiation:
- occurs when many species arise from one ancestor as they adapt differently to their environments. During adaptive radiation, species can
specialize to fill different niches within the same environment.
Sympatric Speciation:
-occurs without a geographical barrier.
- includes:
1) Balanced Polymorphism
2) Polyploidy
3) Hybridization
Balanced Polymorphism
- : different phenotypes are isolated within the same area.
Polyploidy
-: in plants results from nondisjunction during meiosis. (eg. Two
3n organisms - usually sterile - meet and are reproductively compatible).
Hybridization
- some hybrids are more fit than purebreds.
Theories of Macroevolution include:
1) Phyletic gradualism
2) punctuated equilibrium
Phyletic gradualism
- : evolution happened gradually via accumulation of small
intermediary changes. Not likely to be true (not supported by fossil evidence).
Punctuated equilibrium
- short spurts of evolutionary changes during periods of stasis
(supported by fossil evidence).
Patterns of Evolution
1) Divergent Evolution
2) Convergent Evolution (homoplasy)
3) Parallel Evolution
4) Coevolution
Divergent Evolution
- : species diverge from
common ancestor.
Convergent Evolution (Homoplasy):
- unrelated species adapt to similar
environments becoming more alike
(analogous structures).
Parallel Evolution
- : species diverge from a
common ancestor but undergo similar
changes.
Coevolution:
-two species impart selective
pressure on each other. Classic example is
hummingbirds and flowers.
- includes:
1) camouflage
2) crypsis
3) aposematic coloration
4) mimicry
Camouflage (cryptic coloration)
- : match appearance to environment to avoid
detection. Strictly visual method of
concealment.
Crypsis
- Similar to camouflage, except
includes olfactory (smell) or auditory
methods of concealment (ex. scent
masking, silencing).
Aposematic Coloration (warning
coloration):
- vibrant coloration in
poisonous animals to warn predators.
Mimicry:
- evolving to resemble another species.
- In Batesian mimicry a non-harmful animal resembles a harmful one.
- In Mullerian mimicry, two poisonous animals resemble each other to
warn their predator.
A Phylogenetic tree
- is a branched diagram that
shows inferred evolutionary relationships
between different taxa. A clade is a cluster with
an ancestor and all its descendants. - Phylogenetic trees can either be monophyletic
(an ancestor and all its descendants) or
paraphyletic (ancestor and some but not all of
its descendants).
A cladogram
- is a type of phylogenetic tree that
shows such inferred evolutionary relationships
among various biological species.
An internal node
- is a branch point on a
cladogram, and represents the splitting
(divergence) of a single group into two
descendant groups.
Cladogenesis
- refers to the splitting apart of
evolutionary lineages (formation of new clades).
Anagenesis describes the gradual evolution of
an interbreeding population without splitting.
Parsimony
- means the simpler the evolutionary
explanation, the better. Phylogenetic trees
minimizing evolutionary reversals, convergent
evolution and parallel evolution are preferred.
Polytomy (multifurcation)
- an internal node of a phylogenetic tree that leads to more than two
tips.
