Week 1 Flashcards
What are the 2 key principles of Darwinian evolution?
Descent with modification
Natural selection
What is descent with modification?
All speices, living, and extinct, have descended without interruption form an original form
What is natural selection?
Causal agent of adaptive evolutionariry change
More offspring produced than can survived
Less well adapted individuals contribute less to the next generation
Other than natural selection what is another key mechanism of evolution?
Drift (genetic drift)
What are used as evidence of evolution?
Fossil record
Living organisms
Experimental evolution
What are fossils?
Can be defined as ‘any physical trace of past life’
What are the different types of fossils?
Structures
Trace fossils - footprints, burrows and bite marks
Chemical fossils - lipids from algae found in oils
Unaltered remains - frozen in ice
Where are fossils mostly found?
Normally formed by burial in sediment
How are fossils biased?
Typically hard structures fossilise meaning species that are primarily soft structures are less frequent
What is the oldest fossil?
Bacteria that resemble filamentous cyanobacteria
What do fossils provide?
They provide key bits of evidence (history and patterns) for our understanding of evolution
Fossils allow us to characterise an evolutionary timescale
What types of information can fossils provide?
Morphology
Behaviour
Tracks- walking on the surface, not burrowing
Trail sgaoe suggests a searching pattern
What can fossils show evolution?
Show ancestors of living organisms with many fossils resembling existing organisms
Can have characteristics that are intermediate between different groups
What is an example of intermediate group with respect to bird evolution?
Archaeopteryx - bird like organism but with dinosaurs
What is an example of intermediate group with respect to ant evolution?
Sphecomyrma freyi - has characteristics of both modern ants and the primative wasps (from which ants evolve)
How can fossils show evolution with change in forms?
Characteristics found in existing organisms today appear in a series of stages within the fossil record
How do fossil forms show relationship between species?
Most recent fossils resemble existing species most closely
Forms can be interpreted in terms of evolutionary change
How common is extinction?
Extinction is very common
What are the two main problems of fossils?
Fossilisation is inherently unlikely
The fossil record is extremely incomplete
What is a problem with a lack of infomation from fossils?
Fossils tell us that a wide range of organisms have existed, but little about the process that created them
What is an example of fossils not showing us how lifeforms were created?
Cambrian explosion - a huge array of animal types suddenly appear in the fossil record during the cambrian period with frw intermediates. The cause of the explosion is unknown
How can living forms show evolutionairy history?
Evolutionairy relationships - inferred form living organisms based on traits
What traits are used to show the evolutionary relationship?
Morphology
Ecology
Behaviour
Genetics
What are homologous traits?
They are trait inherted between two species shared by descent Divergent evolution
What are analogous traits?
Traits evolved independantly
What are the different types of morphological differences?
Among species (inter-specific)
Within species (intra-specific)
How can evolution of morphological traits be shown?
Through the use of an evolutionary tree going from an ancestral state to derived state
What is defines the each node?
Each node is based on the absence/presence of homologous characteristic
What is a key trait about the genetic code?
The same universal genetic code is used in almost all organisms
What are the differences in species with genetics?
Differences between organisms accumulate through mutations
Differences is related to evolutionary time between them
Few differences = closely related
Many differences = distantly related
What are the key traits of a evolutionary tree?
The lines connecting these organisms in the tree are telling us about their past
Nodes tell us about a hypothetical common ancestor
Divergence of lines after nodes represents speciation events
Are genetics a better trait to use?
Less homologous/analogous confusion
Correct misinterpretations based on morphology
Add timeline to events
Resolve complex evolutionary relationships i.e. the relationship between all flowering plants
What is the advanatge of genomics?
It can sequence whole genomes
Where can we get genetics from?
Extract DNA from ancient samples
What places on earth can DNA be found?
Amber preserved insects
Ice-age mammals
Human remains from peat bogs etc
What are problems with ancient DNA?
DNA is an acid - hydrolyses over time.
Human samples - difficult to eliminate contamination by modern human DNA
Requires DNA to be there!
How can evolution be infered?
Infer evolution by observing form and function in populations and species
Mutation (change in DNA) normally happens on a long time scale
But changes in frequencies of alleles at a gene can occur quickly
What is micro-evolutionary scale processes?
Observing populations changing - or comparing across populations subject to
Different pressures - allows us to observe / infer evolutionary change.
What can be used to test and explore the theory of evolution?
Controlled (replicated) experiments across generations to determine the evolutionary response of organisms to specific factors or selection
How can controlled experiments show evolution?
Modification in both phenotype and genotype can be observed in the lab as organisms adapt
What is a long term experimental evolution in mice?
Running performance in mice
(Swallow et al. 1998)
4 selected and 4 control lines
Selected trait – total distance run
What were the results of the long term experiment in mice?
Top 20% of mice used to breed next generation
Physiological and genetic changes after 20+ generations
Results – changes in body and muscle mass, neurotransmitters, gene frequencies
What is macro-evolution?
Large evolutionary changes e.g. origin of new organisms, or shifts in body plans seen in fossil record
What is micro-evolution?
Smaller-scale changes such as base mutations, alterations
of gene frequency within a population (e.g. changes in
frequency of human blood group types)
What is an overview of the fossil record?
Tell us what has existed and when, but incomplete - must be
interpreted with care. Does not tell us about processes
What is an overview of characteristics of livinf organisms?
Tell us about the relationships among organisms living now
Allow us to compare and contrast evolutionary outcomes Limited ability to view evolutionary processes due to time factor
What is an overview of experimental evolution?
Experimental manipulations of organisms with short generation spans
Used to view evolutionary processes at work and test theories and predictions
Why is DNA important?
Fundamental determinant of inheritance
Which bases are purines?
A and G
Which bases are pyrimidines?
T and C
What are the two types of nuclear DNA?
Autosomal - biparental inheritance
Sex chromosomes - human x bi and Y is uni
What are the two types of cytoplasmic DNA?
Mitochondria and chloroplast
What is linkage and why is it important?
Tendancy for loci to be inherited together when near one another on the same chromsome
Less likely to be seperated by recombination
What are the key traits of dominant alleles?
Causes phenotype even if only one copy in genotype (Individual= heterozygous)
Hides the effect of a recessive allele
What are the key traits of recessive alleles?
Effect hidden by dominant allele
Two copies of the allele must be present for the effect (individual = homozygous)
What is the key trait of co-dominance?
Neither allele is dominant. The individual expresses mix of both phenotypes
What determines phenotype?
Determined by genotype and environment
What is pleiotrophy?
A single gene affects multiple traits
What is an example of pleiotrophy?
Phenylketonuria = mutation in a single gene reduced hair and skin pigmentation + also causes cognitive problems
What is epistasis?
Effect of one gene modified by another gene
Genomic level
Phenotypic level - e.g. Albinism (cc)
What are the two strands of DNA called?
One DNA strand is coding - SENSE strand
The other is non-coding - ANTI-SENSE strand
What strand is transcriped?
The sense strand
What is the function of the promoter?
Promoter binds the enzyme RNA polymerase, initiating transcription
What can cause mutations?
Caused by chemicals, irradiation, viruses, or mistakes during replication
What are the types of mutations?
May involve large changes e.g. Chromosome breakages, rearrangements, duplications
Or smaller changes - Single base difference (point mutation) or Deletion/Insertion
What is synonymous substitutions?
No change in amino acid sequence
What is non-synonymous substitutions?
Change in amino acids
What mutations are important?
Only those passed on to the next generation are evolutionary important
What are alleles that are equal fitness called?
Alleles that are of equal fitness = neutral with respect to one another
What are homeotic mutations?
They alter a developmental pathway
What are the common outcomes for mutations?
The majority of mutations have little or no effect (neutral)
Those that do are normally deleterious
Selection normally eliminates deleterious mutations in each generation, but favours the occasional beneficial mutation
What was the difference between control group and drosophila which had no selection pressure?
Selection is reduced in populations of Drosophila- individuals kept singularly and protected
Thus mutations accumulate over generations (genetic load) leading to increased juvenile mortality
What is standing genetic variation?
‘neutral’ or ‘nearly neutral’ variants remain in a population
What happens to mutations in non-coding regions?
Often mutates – and not selected out - so high variation between individuals
What is the variation in functional DNA sequence?
Variants (alleles) may differ between individuals/populations
Inherited in a Mendelian manner (in nuclear DNA)
How do we measure DNA variation
PCR (polymerase chain reaction)
SNP chips
Sanger sequencing
Next generation sequencing
Short read (e.g. illumina) long read (e.g. PACBIO)
Why are neutral DNA used in understanding genetic variation in evolutionary biology?
Within population differences (individual variation)
Between population/species differences
Why are functional DNA used in understanding genetic variation in evolutionary biology?
Between population/species differences
Functional genetics
What is a use of variation in non-coding repeats?
Variation in non-coding repeats between individuals
Why is identifying parentage important?
major importance in evolutionary studies (currency of evolution)
What are types molecular markers?
DNA fingerprinting
Microsatellite profiling
Single nucleotide polymorphisms (SNPs)
What are key uses of identifying parentage?
Quantify the reproductive success of individuals
Determine the adaptive significance of different
strategies and phenotypes
What is extra-pair paternity (EPP)?
Male other than the pair male is the genetic father
What are examples of extra-pair paternity?
Common in birds, average of 15% EPP in
passerine birds (Griffith et al 2002)
Common in mammals, e.g. white toothed
shrews (Bouteiller & Perrin 2000)
How does EPP benefit males and females of a species?
Good genes theory. Females prefer better genetic quality
males – provide better genes for their offspring
Males can gain more offspring if they gain EPP
What were the predictions when studying EPP?
Not all broods should have multiple paternity
Certain males with good genes gain increased EPP
Increased viability of offspring of preferred males
What is required for accurate testing of EPP?
Testing requires accurate parentage assignment
What is an example of ecological changes impacting reproductive isolation?
Reproductive isolation in lake Victorian cichlid
fishes (Pundamilia pundamilia and Pundamilia nyererei)
Increased water turbidity due to agriculture:
May interfere with mate choice
The mechanism of reproductive isolation
Courtship dance and mate recognition
systems among species are disrupted
What happened as a result of increased water turbidity due to agriculture?
Increased interbreeding between Pundamilia pundamilia and Pundamilia nyererei compared with areas of low water turbidity
What is an example of evolution of polnesian land snails?
Splits snails into two clades: Partula and Samoana
Exceptions among the Samoana:
S. strigata & S. ganymedes have thick shells and nonpigmented mantles
Conclusion: Thick shells and non-pigmented mantles have evolved more than once
What is an example of Arabidopsis thaliana with resitance to powdery mildews?
Resistant genotype (RPW8) triggers a cascade of other genes (the Salicylic acid dependent pathway)
Final outcome is cell death around the fungus
Halts fungal growth
