midterm Flashcards
Define evolution
origin of entities possessing different states of one or more characteristics - and changes in the proportion of those entities over time
Define biological evolution
change over timein the proportion of individual organisms within a population differing genetically in one or more traits
Darwin defined evolution as…
descent with modification
What was Platos view on the natural world?
Platonic idealism - there is an ideal form that is imperfectly represented by earthly representations
- ideal forms can be perceived only through contemplation
What was Aristotles view on the natural world?
Essentialism - all members of a class of objects share certain properties that distinguish them from other classes
- species are immutable
- classified species using scala naturae
What was George Cuviers contribution?
- described extinction
Catastrophism - species are created by catastrophic extinction events
Father of palaeontology
What was James Huttons contribution?
- Uniformitarianism - natural processes that operated in the past are still ongoing in the present
What was Charles Lyells contribution
- influence on Darwin
- popularized Huttons uniformitariansm hypothesis
- change can happen on larger timescales
What was Lamarcks contribution?
- inheritance of acquired characteristics
- thought evolution had a goal
- traits acquired by use vs disuse
- transformism
Early influence on Darwin
What were the two main theories in the Origin of Species?
- descent with modification and natural selection
What are the five inter related theories of evolution?
- Evolution as such
-Common descent - Gradualism vs saltations
- Population variation vs. platonic idealism
- Natural selection - mechanism
Why was Darwin wrong about his mode of inheritcance via blending?
would ultimately reduce variation
What are the two main schools of thought on variation of traits?
- Mendelians - large differences - discrete traits - color
- Biometricians - small differences - quantitative traits - height - believed in natural selection
What did Fisher contribute?
- natural selection could work with mendelian inheritance
What is the modern synthesis?
Neo Darwinism
- mendelian inheritance and natural selection
Two types of phenotypic variation
discrete (one loci) and continuous (multiple loci)
Evolution within species and over shorter time scales is known as?
- microevolution
Evolution across species and over longer time scales is known as?
macroevolution
What is the primary ingredient for evolutionary change?
intraspecific variation
Three non genetic forms of inheritance?
- cultural
- maternal effects
- epigenetics
What is cultural inheritance?
- cross generational similarity in non-genetic behavioral traits, based on processes such as non-random imitation
- tool use in non humans
- song learning in birds (language?)
What are maternal effects? (/ parental effects)
- non genetic effect of a mother on the phenotype of her offspring due to factors such as cytoplasmic inheritance, transmission of symbionts from mother to offspring or provisioning.
- hormonally mediated
What is epigenetic inheritance?
- inherited changes in gene expression or phenotype that are not based on changes in DNA sequence
- due to DNA methylation
What is an example of evolutionary trade offs?
- offspring
- generally either many small simple offspring or few larger offspring
Three approaches to determine ratios of inheritance -
- experimental crosses
- correlations among individuals of known relatedness
- common garden experiment - controlled environment
What is a transition mutation?
when a purine is swapped for the other purine or a pyrimidine with a pyrimidine
What is a transversion mutation?
when a purine is switched for a pyrimidine
Define pleiotropy
a single mutation affecting multiple traits
____ is the source of all genetic variation
mutations
Mutations can only be inherited ___
if the trait itself is heritable, and when the change occurs beyond the germ line
Are mutations random or directed? Which experiment shows this?
Mutations are random - the Lederberg experiment demonstrates this- pencillin resistance was already present in certain groups of bacteria before being exposed to it
A _____ mutation has no effect on amino acid sequence, A _____ mutation results in amino acid substitution
synonymous, non-synonymous
Most mutations are ____ but the average effect is _____
neutral, deleterious
Are mutations random or do they arise in response to environmental challenges?
completely random, stochastic, not deterministic
What is a back mutation?
reversion to a wild type allele
Provide four possible ways to estimate mutation rates
- screen offspring of genetically characterized parents over multiple generations
- score mutations after several generations (must account for selection)
- indirect comparison of number of fixed mutations across species (u = D/2t)
- Direct comparison of DNA sequences
Roughly, what is the average mutation rate per gamete per generation?
10^-6, 10^-5 mutations per gamete per generation
The average new human contains roughly how many mutations?
~70 new mutations, 2.2 deleterious mutations, .02 beneficial mutations?
The larger the _____ the higher the ____ _____
The larger the genome, the higher the mutation rate
(does not apply to viruses)
Can mutation rates be subject to selection?
Yes, mutations in proofreading genes can make them better or worse, affecting general rates of mutations
Define genotype frequency
proportion of individuals in a population that carry a specific genotype at one or more loci
Define allele frequency
Proportion of gene copies in a population that are a given allele ( = probability of selecting this allele when a gene s taken randomly from the population
Change in allele frequencies = ?
evoultion
The average phenotypic effect of mutations is ____
deleterious (as an evolutionary consequence)
Define population genetics
study of frequency of alleles in a population and the causes of variation in these frequencies
What is the Hardy Weinberg principle?
In a population of randomly mating individuals allele frequencies are conserved and in equilibrium unless external forces act on them
Define incomplete dominance?
Heterozygote is a blend of the dominant and recessive phenotypes
Allele frequencies are _____ by genotype frequencies
are NOT influenced
How many generations does it take to return to HWEQ?
1 generation (under simple traits that are not sex linked)
What is the maximum frequency of heterozygotes in a population?
0.5
Two implications of HWEQ
- HWEQ is established after one generation of random mating
- Following establishment of HWEQ, genotype and allele frequencies remain unchanged from generation to generation
What are the assumptions necessary for HWEQ? (5)
- Random mating
- Population is infinite
- Population is closed
- No mutation
- No selection
Define genetic drift
Random changes in the allele frequencies in a population due to sampling error
Is the effect of genetic drift stronger in smaller or larger populations?
smaller
What is the average time to fixation of a newly arisen mutaton?
4N generations
The probability that a population will become monomorphic for one allele is equal to ________________
the initial frequency of that allele
Heterozygosity ___ as the frequency of one allele approaches 1?
declines - H = 2p(1-p) (((1-1 =0) so no 2pq
6 influences on effective population size
- variation in number of progeny
- sex ratio
- natural selection
- cross generational inbreeding
- fluctuations in population size (especially during founder effects)
- type of mating system
Define effective population size
number of individuals in an ideal population in which all adults produce equal number of gametes that produces the rate of genetic drift seen in the real population
- harem dominated mammals - some male gametes are not represented
What is the relevant conclusion of the neutral theory of molecular evolution
Rates of neutral mutations in non coding alleles is the most common type of mutation - most mutations are synonymous
- says that on mutations that dont affect the phenotype - genetic drift is responsible for the changes
- looks at genes instead of phenotypes
- similar to genetic drift
What is the inbreeding coefficient?
F - the probability that a random pair of gene copies, inherited by offspring from two parent is identical by descent
What does inbreeding result in in terms of frequency of genotypes?
Inbreeding results in heterozygote deficiency
What two factors make inbreeding have negative effects on the phenotype?
- exposure of deleterious recessive alleles
- loss of heterozygote advantage
Define selection (again)
Differential fitness - survival / reproductive success - of classes of entities (individuals) that differ in one or more characteristics
Evolution by natural selection occurs if (3)
- individuals in a population of entities (organisms) display phenotypic variation
- fitness differences correlate with phenotypic differences (selection)
- correlation between parent + offspring (heritability)
Can you have evolution without natural selection?
yes - genetic drift - what the neutral theory talks about, genetic drift alone will likely affect non phenotypically relevant genes- can act on things that impact the phenotype
Define fitness
the success of an entity in producing representatives in subsequent generations ( a combination of survival and reproductive success )
3 components to fitness?
- probability of survival to reproductive age (and across multiple reproductive periods)
- average number of offspring produced via female function
- average number of offspring produced via male function
Four different levels of selection?
- Individual selection - non random differences among different phenotypes (or genotypes) within a population in their contribution to subsequent generations
- Genic selection - single gene is the unit of selection, such that outcome is determined by fitness values assigned to different alleles
- Group selection - differential rate of origination or extinction of whole populations (or species) on the basis of differences among them in one or more characteristics
- Species selection - species with different characteristics increase by speciation or decrease by extinction in number at different rates
Generally, what is the strongest level of selection?
individual over group selection
What did Carolus Linnaeus create?
Established the framework for modern taxonomy in systema naturae
Who were Darwin’s three main influences?
Lamarck Lyell and Malthus
What was Thomas Malthus doing?
Theories on eugenics ( he liked it)
Influence on darwin
Argued that selection pressure is competition for resources like food
Who was Alfred Russel Wallace
Similar studies to Darwin - did not come from money like Darwin did
Wrote to Darwin in 1858 nd presented with him in the same year
Influenced by transmutation of species (Lamarck)
When was The Origin of Species published?
November 1859
Three conditions for evolution by natural selection
Phenotypic variation, heritability and effect on fitness
What is this formula? pt=1/2N?
frequency of a newly arisen allele
What is the formula = u0 x 2Ne?
number of new mutations that arise in a diploid organism where Ne is the neutral mutation rate
What is the formula = 1/(2Ne)
probability that a mutation will be fixed by genetic drift
Whst is the formula = (2Neu0) x (1/(2Ne)) = u0
number of neutral mutations that arise and will someday be fixed
What is the alternate formula of frequency of heterozygotes that is used to calculate F?
F = 1- (H/H0)
- the actual frequency of heterozygotes over the frequency if the population was in HWEQ
How do you do an indirect comparison of mutation rates?
U=D/2t where D is number of diff alleles and T is time since divergence
