Evolution Flashcards
What is Mendel’s first law?
alleles can be dominant or recessive
What is Mendel’s second law?
assortment is independent/ alleles are transmitted independent of each other if they are on different chromosomes
What are Darwins 5 theories
Evolution occurs, species multiply, common descent, natural selection, gradualism
What is evolution?
Descent with modification. All species have a common ancestor. Evolution produces complex phenotypes and new species
How does evolution occur?
Mainly by natural selection of existing variation: the preferential survival of the organisms better adapted to their environment
What 3 observations does Darwin make about organisms and what was his conclusion?
geographic similarities, animals are anatomically similar and that animals look very similar in their embryonic stage. Conclusions - all species on Earth had a common ancestor
What observations does Darwin make which leads him to conclude that evolution was driven by natural selection
Fossils show that most species went extinct
There is survival for competition because there are excessive amounts of offspring and limited resources but still there are stable population sizes.
Humans have used artificial selection to produce variation, so species can change under selection
Define natural selection
a mechanism that results in the survival and reproductive success of individuals best adjusted to their environment and that leads to the perpetuation of genetic qualities best suited to that particular environment
What can we conclude if population is not in Hardy-Weinberg Equilibrium
We can conclude that the population is undergoing selection, migration, or assortative mating (or is not large enough, or mutation rate is very high
How does population size affect natural selection
Natural selection is more effective in large populations and the effect of genetic drift is more prominent in small populations which can cause favorable alleles to go extinct
What is runaway selection
When females prefer to mate with a showy male, resulting in her sons being showy males and the daughters preferring showy males, increasing the reproductive success of the males creating a positive feedback loop
Define epitasis
Interactions between genes (which aren’t alleles), often referencing how one gene may suppress another resulting in a change in phenotype`
What is genetic drift
It is a mechanism of evolution which, unlike natural selection, is when allele frequencies in a population fluctuate due to chance
What are non-sex chromosomes called?
Autosomes
What are the consequences of allele on an autosome if its not in H-W equilibrium
H-W equilibrium will be reached in one generation
Directional selection favours which individuals?
Those at one end of the distribution of a trait
Stabilizing selection favours which individuals?
Those near the mean of the distribution of a trait
Disruptive selection favours which individuals?
Those at both ends of the distribution of a trait
What is the Hardy-Weinburg Law?
Allele frequencies will not change across generations if there is random mating, an infinite population (or the equation would not be true),no gene flow, no selection and no mutation
How do you work out frequency after the selection?
Frequency before selection x relative fitness
What is the mean fitness of the adult population if the aa genotype is deleterious?
p^2(1)+2pq(1)+q^2(1-s) or 1−sq^2
How do you work out the frequency of genotype after selecton when you know the frequency before selection and the relative fitness, e.g AA
Original frequency x (AA’s fitness / average fitness)
or
p^2 x (1/1-sp^2)
When calculating relative fitness, what terms can ‘before’ frequency and ‘after’ frequency be replaced with
before = observed after = expected
What are the benefits of sex
Allows for out-crossing and recombination which results in variance
What is the Red Queen Hypothesis
A theory which suggest that species need to continuously evolve in order to keep up with competition. If they stop evolving, they will lose to species which do. e.g hosts need to continuously evolve in order to become resistant to a parasite, which needs to continuously evolve in order to overcome such defenses. it is used to explain why sexual selection occurs
Explain Fischer’s evolution of stable sex ratios
- Suppose males are less common than females.
- A male will have higher chance of mating than a female.
- Parents producing more males will have higher fitness.
- Genes for male-producing tendencies will spread.
- Male births will become more common…
- …until we reach the 1:1 sex ratio.
- The same argument holds if females are substituted for males.
- Therefore 1:1 is the equilibrium sex ratio.
What is an evolutionary stable strategy?
a strategy which if adopted by all members of a population cannot be invaded by a mutant strategy through the operation of natural selection.
What are the to configurations in biological games
Monomorphorism one phenotype has taken
over the population, it was fitter than the others
and dominates.. e.g all hawks
Polymorphism: there are multiple phenotypes
in a population, all reinforcing the presence of
the others. e.g a stable ratio of hawks and dove
What is frequency-dependent selction
Selection where the f fitness of a genotype depends on its frequency.
Explain the process of frequency-dependent selection and give an example
When a genotype is rare, it is relatively favored by selection and it will increase in frequency; as it becomes more common, its fitness decreases and there may come a point at which it is no longer favored. At that point, the fitnesses of the different genotypes are equal and natural selection will not alter their frequencies: they are at equilibrium. The sex ratio is another case in which selection is frequency-dependent.
What is the handicap principle and give examples
A theory which suggests that certain signals are costly and thus cant be bluffed, therefore they are reliable indicator of quality. Low quality specimens could not afford to give of the same standard of signal as high quality e.g an impala stotting to show off it’s quality to a predator or a bird of paradise dancing with its elaborate feathers
Explain the process of Fishers runaway selection
For what ever reason some females have an underlying
preference for males with an exaggerated trait. Sons of choosy mothers have the exaggerated trait and carry
the tendency to be choosy. Daughters tend to be choosy, and carry the tendency for the exaggerated male trait. Therefore exgagerated traits (in males) and the preference for exaggerated traits (in females) will coevolve in a positive feedback [“linkage
disequilibrium”] and reinforce heach other
What is linkage disequilibrium
The nonrandom association of alleles at different loci
What are the 4 ways to answer the question why do male birds often have bright colors or long feathers?
Ontogeny (during development) Overtime Proximate
Phylogeny (over generations) Overtime Ultimate
Mechanism (immediate causation) Current Proximate
Adaptation (fitness function) Current Ultimate
Is the interest of a gene always aligned with the interest of the individual
No
What is intragenomic conflict
When selfish genetic elements distort the standard rules of inheritance to gain a transmission advantage over other parts of the genome, often at the expense of the host organism itself.
Give an example of intragenomic conflict in nuclear genes
Conflict between chromosome A and B in the grasshopper Eyprepocnemis ploran. The B chromosomes cause the disintegration of the chromosomes accompanying
them in the spermatozoa, thus reducing to zero the
fitness of the host genome
What is a b chromosome
It is a parasitic chromosome not necessarily present in most of the species population and are not needed for basic life functions like A chromosomes. It is transmitted in higher-than-expected frequencies, which leads to their accumulation in progenies.
What is meiotic drive
When one copy of a gene is passed on to offspring more than the expected 50% of the time. It is a type of intragenomic conflict, whereby one or more loci within a genome manipulate the meiotic process in such a way as to favor the transmission of one or more alleles over another, regardless of its phenotypic expression.
What is a segregation distorter?
A gene which does not follow the usual process of meiosis and is instead present in more than half of the gametes
What happens is a segregation distorter is present on the sex chromosomes?
It will lead to an uneven sex-ratio, which can lead to population extinction
What is kin selection?
It is a evolutionary strategy that favours the reproductive success of an organism’s relatives, even at a cost to the organism’s own survival and reproduction.
What is inclusive fitness
the ability of an individual organism to pass on its genes to the next generation, taking into account the shared genes passed on by the organism’s close relatives.
What is allopatric speciation?
(geographic speciation) speciation that occurs when biological populations of the same species become isolated from each other to an extent that prevents or interferes with genetic interchange.
What is sympatric speciation
speciation that does not require geographical isolation to restrict gene flow, such as a population occupying different niches
Give an example of sympatric speciation
Apple maggot flies used to only lay eggs on hawthorn bushes (which are native to America) and domestic apples (which were introduced to America by immigrants and bred). Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates on the type of fruit they grew up in. So hawthorn flies generally end up mating with other hawthorn flies and apple flies generally end up mating with other apple flies.
What is allopoidy
speciation which occurs when two species hybridize. If the resulting hybrid offspring has an odd number of chromosomes, it wont be able to reproduce sexually
What is a clade?
anorganism and all its descendants/ a branch of a phylogentic tree
What are homologies
Similarities due to common descent
Why do we get disease X (proximate/how plan)
Ontogeny - Developmental explanations for changes in individuals, from DNA to their current form which could have lead to the disease
Mechanism (causation) - Mechanistic explanations for how the disease formed
What is mutation accumulation?
It is when harmful mutations accumulate over evolutionary time because there is no/weak selection against them due to the fact their deleterious effects only show later in life after the animal has reproduced
What is Antagonistic Pleiotropy.
When one gene controls for more than one trait where at least one of these traits is beneficial to the organism’s fitness and at least one is detrimental to the organism’s fitness.
Why do we get genetic diseases?
- Diseases may reflect our evolutionary history
- Intragenomic conflicts
- There is no selection against certain diseases
Explain why we get genetic diseases in term of our
evolutionary history and genetic drift and give an dxample
Isolated populations can be victims of genetic drift which can make harmful mutations more common. Around 1775 a typhoon reduced the population of Pingelap to 20 people; one carried and allele for achromatospsia resulting in 5% of the current pop. being colourblind
Explain how evolutionary history can affect our responses to medicine and give an example
Genetic variation can result in different responses to drugs. Warfarin is used to destroy blood clots, however those carrying the rs9923231 allele of the gene VKORC1 will uncontrollably bleed is given the standard dose. 100% of Hans Chinese have this allele whilst only 10% of Africans did. Strong evidence had been found to suggest that this is due to natural selection, although the cause is not clear
What explains the differences in lifespan
observed in different species?
Extrinsic mortality rates affect the strength
of selection at different ages.
