Evolution Especiale Flashcards
What is bootstrapping?
- using an original phylogenetic tree, we take multiple random sequences and form thousands of trees
- we then can compare the amount of trees that represent the same groupings as the original tree
- > 70% is a good grouping, consistent values that reprint the original data set is close to accurate: increased likelihood and probability
Describe blended and particulate inheritance in terms of genetic variance
- blended inheritance reduces genetic variation (combines them, cannot uncombined)
- Particulate inheritance: maintains genetic variance (can combine traits but alleles remain separate - this is how variation persists in a population)
What functions do proteins serve?
- Transportation
- structural function: maintains ECM and cytoskeleton
- enzymes: intimates and regulates chemical reactions
- intracellular signalling
- regulates DNA expression
What are regulatory elements?
section of the DNA strand that controls the rate of transcription and therefore the extent of gene expression
- associated with how DNA is wound around histones (packed too tightly can prevent access to promoter region and block transcription)
What is epigenetic inheritance? What is one method of epigenetic inheritance?
- heritable mechanisms that alter gene expression without altering the DNA sequence
- in germ lining, secondary process that impacts the histones and inhibits transcription
methylation: adds a CH3 group to G-G bonds - they interact with proteins and alter chromatin structure: highly methylated regions make RNA polymerase unable to bind
What are the methods of epigenetic inheritance in individuals?
- cell differentiation: methylation and changes in histone modifications alter gene expression
- X chromosome deactivation
What is maternal antibodies an example of?
- epigenetic inheritance across generations: mothers resistance to pathogen from experience can be passed on to offspring!
What is developmental plasticity?
- the altering of genes based on environmental conditions in utero : mother’s diet can increase risk of child developing metabolic disease later in life
How are heritable mutations transferred to offspring?
- through the cell germ lining
What are rates of mutation dependant on?
- genome size and organism size
What are the conclusions of HW equilibrium ?
- A and a frequencies will remain constant
- we can predict genotypes from allele frequencies
- An allele not in HW equilibrium will reach HW equilibrium within one generation
If a locus is at HW equilblirum is it guaranteed to stay that way?
- no the population may not remain at equilibrium (HW equations can be used on any population though)
What is balanced polymorphism? In which processes do we see it?
- balanced polymorphism is stabilizing equilbirum: alleles are stabilized in frequency
- occurs in overdominance, where heterozygotes have a higher fitness
- also occurs in frequency dependant negative selection
What are the effects of mutations on allele frequencies in the absence of NS?
- little effect!
What are the effects of mutations and NS ?
Greater effect: mutation selection balance is when the mutation rate is countered by NS evenly
How does migration affect island natural selection and fixation?
- migration prevents localized adaptations from holding
- as long as migration is coming into the land, the alleles cannot be fixated - the only way for allele frequencies to remain is for the frequencies to have no difference between mainland and island
- speciation is a potential way for the alleles to become fixed
Dissassortative mating?
- where individuals prefer mates with different genetic and phenotypic traits
- example: MHC loci are associated with the immune system highly polymorphic - mammals tend to make with different alleles than self, detected via olfactory (smell) cues
Sweaty T-shirt study: women preferred sweat smell of those who have genes more dissimilar to their own
What are the consequences of drift?
- Drift and allele frequency
- Drift reduces variation (increase homozygosity)
- divergence among populations (its random so different population will have different fixed alleles)
What are the qualities of an ideal population?
- equal number of males and females
- same number of offspring
- random mating
- the same number of breeding individuals every generation
- rate of heterozygosity in a real population is equal to the rate in an ideal smaller population
What are the assumptions of neutral theory?
- At the molecular level …
- variation within the population is neutral
- changes in DNA and amino acid sequences are selectively neutral over time
Describe neutral theory
- Describes most mutations as deleterious but they are removed quickly - so the majority are neutral mutations that are changed or fixed by drift!
- BUT ns is still occurring but isn’t the main driver of change of evolutionary change - positive and purging selection alter the amount of synonymous and non synonymous mutations
- this means that when only drift is acting, the rate of mutations are the same because it is random
- if NS is occurring then rates will change dN/dS within and between populations
How do we determine new frequencies form genotype frequencies after selection?
- first must calculate the p and q alleles and THEN recalculate genotypes -
What are the costs of sexual reproduction?
- it is the norm BUT
- reduced amount of genetic info is passed on
- two fold cost of sexual reproduction
- cost to search for mates, court mates, less vigilant to predators, can contract parasites, recombination breaks up combinations favoured by NS
What are the positives of sexual reproduction?
- removes deleterious mutations (muller’s ratchet)
–> produces genetic variability:
- faster adaption - fisher-miller hypothesis
- sex and unpredictable environments (>1 offspring studied to their environment, and less competition between non-identical genotypes)
- red queen hypothesis: sexual genotypes can outcompete pathogens
What are the assumptions of the red queen hypothesis?
1) oscillations between in relative frequency of sexual lineage when parasites are present : initial resistance, may increase in frequency, pathogen will overcome the adaption of the asexual hosts
2) time lag between the emergence of en effective host defence and and effective pathogenic counter defence
3) increase sexually reproduction relative to asexual ins response to increased pathogenic load
What are most mutations?
- deleterious but they are removed!
What is the rate of synonymous and non synonymous mutations in neutral theory?
- the same: only impacted by genetic drift
what are the reasons that a mutation may be selectively neutral?
1) non coding regions
- pseudogenes
2) synonymous mutations (create variation but no fitness consequences)
3) non-synonymous mutations : will cause mutations because it does change the protein structure but if its further from the binding site less fitness consequences
What is the red queen hypothesis?
- sexually reproducing host lineages outcompete asexually reproducing host lineages
- sexual lineages must “keep running”: genotypes have to change to keep up with pathogen adaptations
Describe the pre Darwin scientists and Darwin himself
Erasmus Darwin: described evolutionary change and the struggle for existence
Chambers: principle of progressive development: new species must arise from old species
- diversity of species changes over time, very gradual
- populations evolve not individuals
Lamarck : inheritance of aquired characteristics
Charles Darwin:
- Explained natural selection: the environment selects of certain traits that have a higher fitness
- all species arise from one (or a few) common ancestors
What is the Fischer-muller hypothesis?
- predicts that sexually reproducing populations will evolve more rapidly than asexual
- arises from sexual reproducers’ abilities to recombine and create allele with decreased mutations
- asexuals need to develop those mutations entirely independantly
What is the fossil record?
History of life on earth indicated by fossil evidence
What does balanced polymorphism mean?
Regardless of where A1 begins it will reach a stabilized equilibrium
- associated with balancing selection: a1 and a2 are equal in frequency
Describe the associated experiments with variational and transitional processes? What is evolution?
- transitional process: all parts must be converted, Lamarck’s inheritance of acquired characteristics
- variational process: evolution is a variational process, ‘sifts’ out certain individuals : natural selection!
What are the processes which change allele frequencies?
- mutation, migration, genetic drift and non-random mating all cause all frequencies to change and drive adaptive evolution
