Lectures 1-10 Flashcards
two controversial ideas of evolution
concept of a changing universe, a phenomenon with no purpose
early ideas about evolution
earth formed according to the laws of physics and chemistry
life emerged as distinct types (not true)
paleontology provided evidence that life changed
fossils
fill in the gaps of extinct forms we don’t see today
co-discoverers f natural selection
Charles Darwin and Alfred Russell Wallace
darwin
voyage on the H.M.S Beagle (1831-1836)
layed the foundation for plant and animal studies
wrote 25 books
importance of islands in evolution
their isolation means many of the living organisms found on islands are unique to them (prevents migration)
preservation of favored races in the struggle for life
all organisms have descended with modification from common ancestors
founder of taxonomy
carl linnaeus
hierarchical system of classification in order from largest to smallest
Kingdom-Phyla-class-order-family-genera-species
taxa at the tips of phylogenetic trees
are all alive and have been evolving for the same amount of time
Monophyletic group
includes an ancestor and all of its descendants (the type we want)
paraphyletic group
includes ancestor and some descendants
polyphyletic group
includes two convergent descendants bot not their common ancestor
phylogenetic trees
hypotheses about relationships between taxa
can be done at any taxonomic level
are constantly reevaluated
homoplasy
common problem (only 4 character states so the probability of separate lineages independently arriving at the same character can be high)
when species have the same mutation but were independent events
convergent evolution
significance of genes that differ in rate of evolution
slowly evovlving genes are useful for distantly related species
rapid evolving genes are useful for closely related lineages
parsimony
simplest explanation is most likely the right one (use when making a tree)
using traits (DNA) in a tree
traits that all species share are not useful for inferring phylogenies
traits that only one species has are also not useful
most useful characters are shared derived traits
homology
traits that are shared because they are inherited from a common ancestor (homologous)
synapomorphies
shared derived traits that evolves in the common ancestor
sources of genetic variation
mutation (ultimate source), recombination, gene flow, and hybridization
somatic mutations
affect cells in the body of an organism: not heritable
germ-line mutations
affects gamettes: heritable and relevant to evolution
rates of mutations
depends on type of mutation, the organism and it varies among genes
most common mutation
point
point mutation rate in humans
12 mutations/ billion base pairs
3.2 billion bp in haploid genome
36 mutations from each gam
most mutations are… because…
mildly bad
genomes work very well, billions of years of evolutions
more ways to mess things up than to fix them
possible gamete combinations in humans
8 million (2^23), meiosis generates variation (independent assortment)
where does majority of genetic variation in a populations come from
sexual reproduction
evolution
change in allele frequencies through time
hardy Weinberg equilibrium equations
q^2 + 2pq + p^2 = 1
p+q=1
predicting genotype frequencies, ie. what is the probability that a zygote will be AA
probability of the egg being A * probability of the sperm being A = probability of AA
0.6*0.6=0.36 (p^2)
p^2 + 2pq + q^2 = 1 means that
your math is correct not the the population is in HWE
5 Hardy-Weinberg equilibrium assumptions
no selection, no mutation, no migration, no chance events, and random mating
Hardy-Weinberg equilibrium principle
allele frequencies do not chnge between generations, single generationn of random mating establishes H-W proportions
given the number of individuals with each genotype or frequencies. and you are asked whether the population is in HWE
write out observed genotype frequencies
use observed to calculate allele frequencies (p + 1/2 2pq, ect)
calculate expected genotype frequencies using allele frequencies
p and q are
allele frequencies
p^2 , 2pq and q^2 are
genotype frequencies
2pq has a maximum value of … when p = q = …
0.5
alleles are lost more rapidly in ..
small populations
allele changes are less predictable in ..
small populations
properties of genetic drift
one allele will eventually be fixed, tends to remove genetic variation, direction of change can not be predicted and the probability that a particular allele will eventually be fixed is proportional to its frequency in the population
rare alleles are primarily found in
heterozygotes
drift causes … but not …
evolution but not adaptive evolution
fitness
the expected reproductive success of an individual with a particular phenotype
factors of fitness
survival to reproductive age, mating success and fecundity
relative fitness
fitness of a genotype standardized by comparison to other genotypes
w
calculate the relative fitness of a genotype by dividing it by the fitness of the most fit genotype on the population
relative frequency at reproduction is =
new Wa1a1/ bar W
natural selection is more powerful in ___ populations because _______ is weaker
large
genetic drift
s
selection coefficient
= fitness disadvantage to genotype
Waa= 1-s
h
dominance coefficient
= proportion of s applies to the hetero genotype
WAa = 1 - hs
overdominance
heterozygote advantage
maintains variation and both alleles
underdominance
heterozygote disadvantage
removes variation
negative frequency dependent selection
an allele becomes lee fit as it becomes more common
promotes genetic diversity
allele dominance often go through cycles
both alleles are maintained
positive frequency dependent selection
an allele becomes more fit as it becomes more common
leads to unstable polymorphism
difficult to study
as soon as one allele becomes more common it goes to fixation
inbreeding
self fertilization, sib mating, etc.
reduces heterozygosity
two types of inbreeding
disassortative mating and assortative mating
disassortative mating
genotypes that are different may mate one another more often than expected
assortative mating
genotypes that are similar may mate more often than expected
inbreeding can be eliminated with one …
round of random mating
inbreeding coefficient
probability that two alleles are identical by descent
in each round of inbreeding heterozygosity is
reduced by half
inbreeding changes
genotypes not alleles/allele frequency (not a type of evolution)
F =
1- (Hobs/Hexp)
inbreeding depression
reduced vigor, longevity, fertility, etc. by exposing recessive alleles
difference between inbreeding and assortative mating
inbreeding acts on the whole genome simultaneously
alternative mating, which only acts on the loci associated with the traits
(both mate with preference for a genotype)
events required for gene flow
gene movement and gene establishment
gene movement
movement of individuals and movement of their gametes
gene establishment
survival and reproduction
direct methods for measuring gene flow
mark recapture in natural populations
indirect methods for measuring gene flow
molecular marker variation
analyze differences in allele frequencies
genetically differentiated
when populations differ in allele frequencies
when two adjcent populations are genetically differentiated this tells us that
gene flow has not homogenized them
Fst
measurement of differentiation
measures variation in allele frequencies among populations
ranges from 0-1
compares the average expected heteroxygosity of individual subpopulations (S) to the total expected heterozygosity (T) if the subpopulations are combined
= 1 - (Hs/Ht)
calculating Ht
calculate the mean of p
calculate the mean of q
Ht = 2(pmean)(qmean)
Fst = 1
most extreme subdivision
calculating Hs
calculate 2pq for each population
mean (2pq)
gene flow balances with ____ causing populations to be ____
genetic drift
differentiated
genetic drift VS genetic flow
population subdivision enhances the effects of drift (divergence in allele frequencies)
gene flow counteracts subdivision by homogenizing allele frequencies (more similar among populations
population subdivision causes some level of ____ because ____
inbreeding
it has a reduced mating pool and more alleles are identical by descent
