Evolution Flashcards
What causes evolution?
Accumulation of genetic variation
History of Evolution
Greeks –> Carolus Linnaeus (hierarchy based on common features, animalia, chordata etc.)
Lamarckism (living beings could acquire characteristics over their life and pass these down)
Nicolaus Steno (fossils showing evolution)
Mary Anning (species could go extinct)
Darwin (theory of natural selection)
Darwin (sexual selection)
Evolution Definition (CD)
The cumulative change in the genetic composition of a population or species over time
The 3 pillars of Darwinian Theory of Evolution
- Species are not immutable
○ Population show phenotypic variation and species can change over time
○ Difference in and between species- Descent with modification occurs
○ Related species, which share a common ancestor, diverge from one another gradually over time - Natural selection
○ Differences in phenotypes of individuals cause some of them to survive and reproduce more
○ Not all organisms produce offsprings, the more adapted to the environment you are, the more offspring you can produce, increasing genetic/phenotypic occurrence
- Descent with modification occurs
Explain natural selection? What does it act on?
Individuals with phenotypes most suited to the environment (fittest) are more likely to produce offspring.
Natural selection is the driver of evolution and acts on heritable variation within a population
What is a phylogeny? What groups/relationships can it represent?
A phylogeny is a physical representation of evolutionary relationships of species
Monophyletic:
includes the common ancestor and all descendants (a clade)
Polyphyly
does not include common ancestor
Paraphyly
includes the common ancestor, but not all the descendents
Terminology of phylogeny
Nodes
represent the msot recent common ancestor
Terminal Branch
leads to taxonomic group *only one species
Internal branch
leads to many other groups/species
Macro and microevolution
macroevolution:
explains the evolutionary changes among large taxonomic groups above the species level
includes:
origin, diversificationa dn extinciton of species over long periods of time
Convergent evolution
when two species evolved separately but formed similar morphological traits
What are the 6 agents of evolutionary change? What do they do?
The 6 agents of evolutionary change are:
- mutation
- gene flow
- genetic drift
- natural selection
- non-random mating
- recombination
They effect and cause evolution in species
Mutation- what is it?
Changes in an organisms DNA that can introduce new alleles. They have to be heritable (to the germ line cells) and can then contribute to the allele frequency in populations, changing the overall species
How do mutations arise?
During DNA replication there can be mistakes, they can also occur from mutagens (chemicals that cause mutations) or radiation damage
There are 2 sources of external damage
- exogenous (UV, radiation, chemicals etc.)
- endogenous (reactive oxygen species, hydrolysis, alkylation, endonucleases)
If the mistake isnt repaired this can cause mutation
What are the types of Mutations
- point mutation
single base change - insertion/deletion
DNA of different sizes is inserted/deleted from an existing sequence - Frameshift
a section is added or deleted, causing everythign to be moved over (codons) - larger mutations
DNA is copied an extra time, flipped aroumd, chromosomes are gained or lost (aneuploidy). They are less common because they lead to death more often
positive and negative mutations are known as?
advantageous and deleterious
Somatic and Germline mutations
germline
affects gametes
passed on through sexual reproduction
somatic
affects all of the daughter cells of a single cell
not heritable (can be passed down through plants and vegetative reproduction)
cancer
How often do mutations occur for evolution to occur?
○ If the mutation rate is too low then there is no evolution or adaptation (risk of extinction in new conditions)
○ If its too high then too many functional alleles are effected
○ 10-8 mutations per nucleotide per generation (of single nucleotide changes)
○ 50-70 changes per individual at birth
○ 3.2x109 nucleotides in the human genome
○ Almost 4 times more mutations from the father than mother (because of Y chromosome mutations)
How do mutations cause evolution?
New alleles arise by mutations, which are created by change in the nucleotide sequence of an organism’s DNA. Mutation creates genetic variation that selection can act upon, which can result in increasing the frequency of adaptive traits, or removing maladaptive traits from the population
Non-random mating
General term used to describe when an individual does not choose mates at random.
Animals can dominate others in order to breed, or pick mates based on certain criteria, therefore changing allele frequency to favour the genes required to fit these criterie
Plants often self-germinate, resulting in increase homozygosity
this decreases genetic variation
What is Genetic Drift?
the populations alleles are separating slowly from their original combo due to random chance e.g. they are drifting
effects smaller populations because there are less things to change to make a bigger impact
It REMOVES variation, rather than adding it
Natural selection as an agent of evolutionary change
Natural selection changes the frequency of genes and alleles in a population and is therefore an agent of evolutionary change
It can help increase beneficial mutations to the environment and sift out maladaptive traits
it a microevolutionary process that shapes the phenotypes of an organism to match its environment
Gene Flow
Isolated populations accumulate genetic differences over time, through genetic drift, selection and mutation
These can lead to reproductive isolation and speciation
Gene flow counteracts the effects of population subdivisions
Gene flow is the process of the spread of genetic variation across geographical areas due to migration, hybridisation or gamete dispersal
Increases genetic variation and can homogenise allele frequencies across the landscape between connected subpopulations
What needs to happen for gene flow to occur?
individuals must be able to disperse, interbreed and produce viable offspring
The populations can be isolated at one point, but gene flow can only occur when there is some way for them to reproduce again
What does the impact of gene flow depend on?
- The genetic difference berween populations
if there isnt a lot of difference, then there isnt a lot of stuff to change/disperse, and vice versa - the level of migration/movement and hybridisation
if there isnt a lot of interaction, then the distribution of genetic material will be slower and vice versa
Recombination
Recombination is the exchange of genetic material that occurs when two chromosomal pairs cross over in meiosis.
This results in the exchange or mixing of the chromosomal regions to create new genetic combinations
Particular combinations of traits may be beneficial. Since recombination creates new combinations of alleles at different genes, and recombination frequencies can vary between genes, the ease at which recombination occurs can affect the speed at which evolution occurs.
Intependent assortment
Paternal and maternal chromosomes inherited by the individual will assort into gamete cells independently during meiosis, creating novel combinations of alleles at different loci
Molecular clocks and phylogenies
molecular clocks can be used to estimate when two species last shared a common ancestor
you can look at morphological changes, protein changes and amino acid sequence changes, however, protein and amino acid sequence changes are more accurate and useful
cladograms vs phylograms vs ultra metric trees
cladograms show clades and topology
phylograms show how much change occurs (longer length is more change)
ultra metric trees use genes adn real time plots
adaptive traits
Particular structures, physiological processes or behaviours that make an organism bettwe able to survive and reproduce
arise through mutation, creating new variation for selection to act upon
can also be passed between related species via hybridisation
examples of adaptive traits (4)
- pollinators
two different types of the same flower attract different pollinators and are seperated by prezygotic reproductive isolation - bee pollinated
nectar guides, wide corollas, inserted anthers and stigma - bird pollinated
red and reflexed petals, narrow tubular corolla, exerted anthers and stigmas
