Evolution Flashcards
Evolution
- The gradual development and change of heritable traits (allele frequencies) within a population over time
- Evolution increases biodiversity
Evidence of evolution
Fossils
Biogeographical
Embrological
Comparative anatomy
comparative biochemical
molecular biology
Paleontology
Study of fossils
What are the two types of fossils?
1) Actual remains of the animal, petrification
2) Traces of animal like footprints, molds, casts (ichnofossils)
Petrification
The process by which living organisms turn into fossils due to the body being buried under layers of sediment - minerals slowly seep into the body and replaces organic material to get a hardened corpse
Evolution: fossils
Allows us to see the development (anatomical changes) of species through time by comparing deepest (oldest) fossils to shallowest (youngest) fossils
evolution: biogeography
Evidence explains the spread of different species throughout the world
Pangea (supercontinent) separated into 7 different continents and caused living organisms to separate - as their environment changed evolution made it so that the organisms adapt to their new habitats
Evolution: embryology
Embryological similarities observed during development stage in related species
Example: all chordates have gill slits at some point in development
evolution: comparative anatomy
- Compares different body parts of different animals that contribute to the identification of an evolutionary relationship
- Three types: homologous, analogous and vestigial structures
Homologous structures
- Structures that may or may not perform the same function but are derived from a common ancestor
- Example: forearm of birds and humans
Analogous structures
Structures that have the same function but are not derived from common ancestors
Example: bird wings and bat wings
Vestigial structures
Structures that exist, but do not serve a purpose in the organism but are homologous to functional structures in other organisms
Example: ostrich wings are homologous to wings of eagles, ostrich do not use them to fly but eagles do
evolution: molecular biology
- Method that allows for comparison of nucleotide and amino acid sequences of DNA and proteins from different species
- Able to see conserved DNA regions across species when comparing DNA sequences (ex: chimpanzees have ~98% similarity with humans)
- amino acids in the protein cytochrom C are often compared
Catastrophism
Baron Cuvier proposed catastrophism through observing fossil patterns
Proposed that sudden catastrophes happened spontaneously throughout history caused mass extinction of species
Different populations shaped by what catastrophes had occurred and the random organisms that survived
After catastrophe, landscape changed and new organisms populated the area
Jean-Baptiste Lamarck
Proposed two theories: use and disuse, and inheritance of acquired traits
Use and disuse theory
The most used a body part is, the more it will develop and the less used a body part is, the more it will weaken
Example: a giraffes neck gets longer the more they stretch it to use it, and the giraffe will give birth to offsprings with long necks
This theory is incorrect
Theory of inheritance of acquired traits
Whatever characteristic an organism acquires throughout its life, it will be passed onto its offspring
This theory is incorrect: the changes are not changing the DNA within an organism and therefore will not be a passed on
Natural selection theory
Proposed by Charles Darwin
Inspired by thomas malthus’ theory of population growth
Unchecked population growth would outgrow available resources which results in Malthusian catastrophe: manny members of population die of starvation, remaining forced to return to basic survival
What are the requirements for natural selection?
1) There is more demand than supply
2) There is a difference (variation) in the level of fitness
3) Traits must be heritable
4) Variation of traits must be significant to reproduction and/or survival
Stabilizing selection
Mainstream (average) is favored and extremes are selected against
Example: average newborn weight
Diagram follows a stranded bell curve
Directional selection
- One extreme is favored (population evolves to favor traits in one direction)
- Example: giraffes with longer necks are able to survive due to ability to get more food from tall trees
- industrial selection: industrial pollution causes the selection of dark-colored moths
Disruptive selection
Extremes are favored, mainstream traits are not
Example: black shelled snails thrive in high vegetation areas, while the white shelled snails thrive in low vegetation areas
Sexual selection
- Non-random mating between a male and a female
- Females favor high quality partners to boost quality of offsprings (limited capacity to reproduce) while males prefer high quantity of partners to increase the number of offsprings
- Traits selected for may be favorable for reproduction but not for survival
- Example: male peacock feathers attract females, but also attract predators
Requirements for a population to be in Hardy-Weinberg Equilibrium:
(Large Random M&M)
Large populations: minimizes effects of genetic drift (random increase or decrease in allele frequencies)
Random mating: individuals do not seek a particular type of individual to mate with wgucg decreases the chance of any allele from changing in frequency
No mutation: prevents new alleles to be introduced to the population
No natural selection: the environment is not impacting allele frequencies and so traits are neutral
No migration: (aka no gene flow) no movement of genes in or out of population (an isolated population has no gene flow)
what does the Hardy-Weinberg formula calculate?
Calculates generic frequency during genetic equilibrium (no change in gene frequencies aka no evolution)
Microevolution
- changes in allele frequencies that occur within a population over generations
- favorable genes increase, unfavorable genes decrease
- due to mutation, gene flow, gene drift, nonrandom mating, and natural selection
Allele frequencies
Indicate how often you find certain allele in a population
Do genes that result in traits being best suited for the environment increase or decrease gene frequency?
Do genes that result in traits not being suited for the environment increase or decrease gene frequency?
Increase
Decrease
Sources of genetic variation:
1) mutation
2) sexual reproduction
3) balanced polymorphism: heterozygote advantage, hybrid vigor, minority advantage
4) diploidy
5) outbreeding
6) neutral variation
7) geographic variation
Genetic variations: mutations
Must not be fatal
Mutations are a way to introduce alleles into a population
Genetic variation: sexual reproduction
- Creates diversity in three ways: crossing over, independent assortment and random joining of gametes
- allows for the removal of deletatrious alleles
Balanced polymorphism
Different phenotypes within population members can be maintained through different advantages:
- heterozygote advantage: the heterozygote form is better suited for the environment than both homozygote forms —> two parents produce an offspring that is more fit than either of them
- Minority advantage: rare phenotypes offer higher fitness than common phenotypes —> cycle between high and low frequencies (ex: advantages against hunters search image)
- hybrid advantage: hybrid (breeding between two different strains of organisms), offspring is usually superior due to combination of different genes
- neutral variations: variations passed down that do not cause benefits or harm to the organism that may come in handy if the environment changes
Genetic variation: Polyploidy
Beneficial because the dominant allele can mask the affect of the recessive allele (ex: diploid organisms with 2 alleles for each gene
More variety and preservation of different alleles in the genome (ex: plants are polyploid, they have multiple alleles for a gene)
Causes of microevolution:
(Opposite of Large Random M&M)
1) genetic drift
2) non-random mating
3) mutations
4) natural selection
5) gene flow
Genetic drift
- A factor causing microevolution
- Change in allele frequencies in a gene pool by chance (random increase or decrease in allele frequency)
- Larger effects on smaller populations
- 2 types: bottleneck and founder
Bottleneck effect
- occurs when the population undergoes a dramatic decrease in size due to a natural catastrophes or other disaster
- population is vulnerable to genetic drift and gene pool is much smaller
- some alleles may be lost
Founder effect
- when some individuals migrate away from population and settle in new location
- smaller gene pool
- Successive generations’ genetic makeup will come from original founders (unique from the original population before migration)
Microevolution: non-random mating
- Individual chooses who they want to mate with (sexual selection) based on certain traits
- Certain traits are favored over other —> increase in allele frequency
- Outbreeding: breeding with individuals which no distinct family ties
- Inbreeding: breeding with relatives
- sexual selection: females choose males based on superior taits
Microevolution: mutation
These heritable changes in DNA have varying effects
Some mutations go into a dormant phase until the environment changes and the mutation suddenly becomes favorable
Microevolution: natural selection
An increase or decrease in allele frequency due adaptations to the environment
Microevolution: gene flow
- The process of moving allele (introducing/removig) between populations through individuals migration which leads to mixing of variations
Mullerian mimicry
When two different poisonous species that have a common predator evolve to resemble each other- makes it easier for the predator to learn to avoid these species
Sympatric speciation
Occurs without the presence of a geographical barrier
Achieved in three ways: balanced polymorphism, polyploidy and hybridization
Hardy-Weinberg equations:
- p2 + 2pq + q2 = 1 –> all individuals sum to 100%
- p + q = 1 –> all alleles sum to 100%
both equations must equal 1 to be in hardy-wenberg equilibrium
speciation:
- formation of new species
- occurs when gene flow is intertupted between 2 sections of a population
allopatric speciation
- occurs when the population is divided by a geographical barrier
- results in prevention of interbreeding between the two populations causing the gene pool to diverge
- population diverges due to natural selection, mutation and geneticc drift
- no interbreeding = new species
divergent evolution
- species originate from common ancestor but become different over time as a result of speciation
convergent (homoplasy) evolution
- unreleated species evolve to share similar trairs due to adapting to similar environments (analogous structures)
parallel evolution
- species that share a common ancestor make similar evolutionary changes after their divergene from the common ancestor
coevolution
- two species impart selective pressure on each other
- each causes the other to evolve, resulting in the evolution of both
- ex: hummingbirds and flowers, predetor and prey
evolution: comparative biochemistry
- Able to see common conserved pathways in related species (ex: Krebs cycle and ETC are conserved in all eukaryotes
monophyletic
- the ancestral species and all its descendants
paraphyletic
- the ancestral species and some of its descendants
polyphyletic
- common ancestor of its members is not a part of the group
synapomorphies
- shared traits derived from an evolutionary ancestor common to all members of a group
analogous traits are an example of ________ evolution
convergent
