Week 3- evolutionary genetics Flashcards
what is a scientific theory
an explanation supported by evidence
what did Darwin hypothesised
that present-day species are descendants of ancient ancestors that have evolved
why do populations change over generations
to become more adapted to their environment
what species are naturally selected
when there is a frequently recurring struggle for existence, any being that varies slightly in a manner profitable to itself, will have a better chance of surviving
when was the origin of species discovered
1859
what is natural selection
organisms with certain inherited traits are more likely to survive and reproduce that those with other traits.
Frequency of alleles in a population can change over time
what theory did Alfred Wallace come up with
similar conclusion to Darwin- survival of the fittest
what was Darwin
A naturalist
what tends to happen to closely related species that occupy different ecological settings
they have different characteristics
what happens to populations that are physically isolated
tend to differ
what were Darwins theories
- All species derive from very different species living in the past
- Species change over time because bearers of different traits have different probabilities of contributing offspring to the next generation
- Splitting of single species into two or more species has occurred (Speciation)
- Evolution occurs by the gradual transformation of populations over long periods of time
what processes are required in natural selection
- competition
- variation
- heritability
- iteration
why is there competition in natural selection
Many more individuals are born than survive
why is there variation in natural selection
Individuals vary in traits directly related to their ability to survive and reproduce
what is heritability in natural selection
advantageous traits are passed on to offspring
what is iteration in natural selection
process is repeated generation after generation over long periods of time
what does the modern synthesis theory state
genes are responsible for the inheritance of characteristics
what does the modern synthesis combine
Darwinian selection and Mendelian inheritance
what is the basic explanation of modern synthesis
populations evolve, not individuals. speciation is usually due to the gradual accumulation of small genetic changes
what does the Modern Synthesis Theory suggest that genes are responsible for
the inheritance of characteristic
what does the Modern Synthesis Theory suggest that speciation is due to
the gradual accumulation of small genetic changes
what do fossils show
that species existed in the past that no longer exist today, and species exist today that did not exist in the past
what do fossils provide solid evidence towards
the fact that organisms from the past are different to those we see today; they show a progression of evolution
what are vestigial structures
an anatomical feature or behaviour that no longer seems to have a purpose in the current form of an organism
how did blind cave fish lose their complex eye structure
adaptation to cave dwelling
what is the vestigial genes in blind cavefish
one of the genes responsible for eye loss in cavefish also increases the number of taste buds on the ventral surface of the head, which helps them find food more effectively
what would natural selection for the increase in taste buds in cavefish promote
blindness
what is homologous
Similarities because they derive from a common ancestral source
analogous
Similarities because they perform a similar function and not because they come from a common ancestor
what are homologous structures
similar structures in organisms with shared ancestry
where are homologous structures derived from
the same common ancestor but may not have the same function
what are analogous structures
Less-related species living in similar environments have similar body forms, though often involving different body parts.
how are analogous structures formed
From variations in a population, the environment selects those that best help an organisms survive in that environment.
what can spines be used for in different species
insulation, camouflage, signalling, sensing, and defence
what does embryological similarities demonstrate
a shared set of genes between groups of organisms, suggesting common ancestry.
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what does comparative genomics demonstrate
shared genes for many traits between related species, suggesting descent from a common ancestor
what does the direct observation of change over time show
through artificial selection experiments, the mean phenotype can be rapidly advanced, and phenotypes can be produced that are well beyond the range of variation in a base population.
what is contemporary evolution/ evolution in ecological time
evolutionary change in response to changing environmental conditions
what is one of the outcomes of evolutionary change
the development of species
what are species
a group of organisms that can potentially interbreed with one another to produce viable, fertile offspring.
what is the outcome of different species interbreeding
often produce sterile or less viable offspring
what are the mechanisms of reproductive isolation
- prezygotic
- potzygotic
what is the pre zygotic mechanism
prevent members of different species from mating to produce a zygote
how does the prezygotic mechanism work
- habitat isolation
- temporal isolation
- behavioural isolation
- gametic isolation
- mechanical isolation
what is postzygotic mechanism
keep hybrid zygotes from developing into healthy, fertile adults
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what is speciation
the process where one species can no longer reproduce with and therefore is different from another species
what is allopatric speciation
geographic separation of populations from a parent species
what is sympatric species
remaining in one location
how does allopatric speciation occur
evolution into two or more descendant species after a period of physical separation caused by a geographic barrier leading to reproductive isolation
what are some some examples of geographical barriers that leads to allopatric speciation
- mountain range
- body of water
- changed landscape
- crossing a pre-existing barrier
what is sympatric speciation
divergence without geographic seperation
how does sympatric speciation happen
- mutation/polymorphism within a species
- polyploidy
how does sympatric speciation happen
- mutation/ polymorphism within a species
- polyploidy
what is polyploidy
heritable condition of possessing more than two complete (homologous) sets of chromosomes
what is microevolution
changes in allele frequencies in a gene pool from generation to generation
what are the causes of microevolution
- genetic drift
- natural selection
- gene flow
- mutation
- non-ramdom mating
what does a reduction in genetic variation lead to
inability to adapt to new selection pressures, because genetic variation that selection would act on may have drifted out of the population
what 2 factors may cause genetic drift
- bottleneck effect
- founder effect
what is the bottleneck effect
leads to reduced genetic variability following some large disturbances that removes a large portion of the population. The surviving population often does not represent the allele frequency in the original population
what is the founder effect
when a few individuals from a large population colonise an isolated habitat which may lead to reduced variability
what is natural selection
differential success in reproduction based on heritable traits results in selected alleles being passed to relatively more offspring
when does natural selection occur
when one allele (or combination of alleles of different genes) makes an organism more or less able to survive and reproduce in a given environment
which mechanisms cause natural selection
- directional selection
- disruptive selection
- stabilising selection
what is directional selection
where one extreme phenotype is more fit than all the other phenotypes
what does directional selection favour
individuals at one end of the phenotypic range and is most common during times of environmental change or when moving to new habitats
what is disruptive selection
where both extreme phenotypes are more fit than those in the middle
what does disruptive selection favour
extreme over intermediate phenotypes, and occurs when environmental change favours an extreme phenotype
what is stabilising selection
where the intermediate phenotypes are more fit than the extreme ones
what does stabilising selection favour
intermediate over extreme phenotypes and reduces variation and maintains current average
what is gene flow
movement of alleles between populations
what tends to happen to gene flow over time
reduction in variation
what does natural selection normally select
pre-existing traits (alleles)
what is a mutation
a change in an organism’s DNA and is represented by changing alleles
what is the original source of variation
mutations
how do mutations affect the composition of the gene pool
mutations can be transmitted in gametes to offspring
what is non-random mating mating
when individuals choose mates non-randomly with respect to genotype
what is positive non-random mating
same genotypes
what is negative non-random mating
different genotypes
what is inbreeding
mating with close relatives
