Final Flashcards
population
-a freely interbreeding group of individuals living together in time and space
gene pool
sum of genetic info present in a population
phenotype
a morphological, physiological, biochemical, or behavioral characteristics of an individual organism
genotype
the underlying make up of phenotypes
locus
a site on a chromosome (or the gene that occupies the site)
gene
allele
an alternate form/ version of a particular gene/ locus
allele (gene) frequency
the relative proportion of a particular allele @ a single locus in a population (b/w 0-1)
genotype frequency
mutually exclusive
-dependent events
-both cannot occur (1+6 + 1/6)= 1/3
-1 or 2
how many alleles per locus?
2
Hardy-Weinberg Law
1.) frequency of alleles doesn’t change from generation to generation (frequency doesn’t evolve)
2) offspring genotype frequencies can be predicted from the parent allele frequencies
HW assumption
1) no selection
2) no mutation
3) no gene flow or migration
4) no genetic drift (large population)(exchange of genes)
5) random mating
what does any violation of HW mean?
evolution
Can HW occur in a gene-by-gene basis?
no
total genomic HWE is exceptionally rare
implications of HW principle
1) a random mating population w no external forces acting on it will reach the genotype equilibrium
2)any disturbance of the allele frequencies leads to a new equilibrium after random mating
3) amt. of variation is maximized when gene frequencies are intermediate
where can most copies of a rare allele be found?
in heterozygotes
4 primary uses of HW principle
1) compute genotype frequencies from generation to generation, even w selection
2) serves as a null model in tests for natural selection, nonrandom mating, etc, by comparing observed to expected genotype frequencies
3) forensic and disease analysis
4) expected heterozygosity- provides a useful means of summarizing the molecular genetic diversity in natural populations
2 ways to quantify genetic diversity in population
polymorphism- proportion of loci w more than 1 allele in pop
heterozygosity- proportion of heterozygotes in a pop. at a SINGLE locus
OR
proportion of loci heterozygous in an individual genome
what does a true null hypothesis mean?
-we are in HWE
-would expect sample of this size to show this much departure (or more) from expectations less than 5% of time
Allozymes
enzymes used as molecular markers to assess different alleles (show high heterozygosity)
previously thought that pop wouldnt be variable because 2 allele would grant “best” fitness
what causes genotype frequency differences?
the randomness due to punnet squares
migration (gene flow)
cause allele frequencies of population to change
- powerful mechanism for small pop. really quickly
-leads to gene flow which tends to homogenize allele frequencies (populations) -> stops process of speciation.
inbreeding
-direct violation of hw because violates random mating due to consanguineous relationships
-causes deficit of heterozygote
-selfing is most extreme form of inbreeding
F coeffcient
-inbreeding coefficient (quantify heterozygosity)
-quantify amount of homozygosity in pop.
1= completely inbred
0= no inbreeding
as it increases, fitness decreases
-heterozygote advantage decreases (because hetz decrease)
inbreeding depression
exposure of rare and/pr deleterious alleles increase
directional NS
-average phenotype moves in 1 direction
-changes average value of trait (increases or decreases)
-variance gets a little smaller
-ex: colored moths
stabilizing selection
-favor intermediates (more fit)
-heterozygote advantage
disruptive (diversifying) selection
-heterozygote disadvantage
-intermediates are LESS fit than extremes
sexual selection
selection that arises from differential reproductive success due to VARIATION in MATING SUCCESS
Bateman Gradient
-describes a selection gradient for mating success
-the steeper it is, the greater the strength of sexual selection
-variability and reproductive success greater in males because females invest more
-females: reaches an asymptote
what did Bateman’s experiment conclude about sexual selection?
stronger in males than females because
1) females have limited eggs
2) males have millions of sperm (fitness only limited by how many females can inseminate)
3)in animals, simply due to size and energy differences between eggs and sperm
anisogamy
a union between 2 gametes that differ in size/ form
the fitness of the sex with a steeper Bateman gradient is more limited by the ________ of mates
number
-more mates more fitness
-sex dominates to get more mates
-usually males
fitness of sex with shallower Bateman gradient is more limited by the ________ of mates
quality
-sex wants offspring of the highest quality. leads to “choice” or “choosiness”
what does limiting resources for fitness mean?
more mates —-> reproduce more
sexual dimorphism
2 different morphologies
1) morphology (body size)
2) physiology (hormonal differences)
3) behavior (birdsong, dance, humans)
primary sex traits= gonads
secondary sex traits= everything except sex organs
differences between the sexes that do not DIRECTLY participate in reproduction
maladaptive traits
-traits that conflict with natural selection
-may increase mating success but also decrease survivorship
ex: big antlers energetically costly to an individual. may slow down animal
5 extra mechanisms
1) scrambles- whoever gets to mate first
2) endurance rivalry- protect mate by being there
3) contests- fighting
4) post-copulatory- sperm competition & infanticide(reproduce w grieving mother)
5) mate choice- offering of nutrition
4&5 happen after sex`
when does speciation occur?
when gene flow doesn’t
how can new species evolve?
1) speciation and evolution
allopatric speciation
sympatric speciation
micro vs macro evolution in terms of speciation
macro-evolution: cladogenesis, speciation
micro-evolution: anagenesis, population new species w same ancestor
allopatric speciation
-population is divided into geographically isolated subpopulations
-physical isolation creates an effective barrier to gene flow —> divergence
1) physical barrier isolates 1 population
2) isolated pop diverges by NS and/or drift
3) hybridization
sympatric speciation
speciation occurs in population that live in same area (ranges of population)
-results in formation of 2 or more descendant species from a single ancestral species
-prezygotic isolation
hybridization
fusion of 2 species to form a new
prezygotic barriers
-ecological/habitat (never meet)
-temporal- mate at different times
-behavioral- courtship
-mechanical (gametic:gametes cant fuse)
postzygotic barrier
-egg and sperm unite, zygote forms, results in HYBRID offspring
-mating between individuals of genetically distinct but closely related populations/species
(reduced hybrid viability, reduced hybrid fertility, hybrid breakdown)
what happens when diverged populations come back into contact and there is still the potential to interbreed?
1) reinforcement to complete reproductive isolation
2) get complete homogenization or fusion -> 2 diverged species fuse into 1 species
3) maintenance of hybrids within a stable hybrid zone
4) hybridization may lead to formation of new species
what does hybridization lead to?
less fit intermediates
what is reinforcement
NS that results in a mechanism to prevent hybridization among individuals of diverged populations that are now in secondary contact
migration
-the movement of alleles among populations
-lead to gene flow
-PREVENTS EVOLUTIONARY DIVERGE OF POPULATIONS
genetic drift
alteration of gene frequencies due to change (stochastic) effects
-result of finite population size
-causes loss of heterozygosity by random fixation of alleles
founder effect
change in allele frequency in newly founded population due to colonization of a few founders
larger pop size _______ it will take to dix alleles by genetic drift
longer
Effective population size (Ne)
numeber of individuals in an ideal populationwhere rate of genetic drift is the same as it is in actual population
-THE NUMBER OF BREEDING INDIVIDUALS IN THE POPULATION
what happens in populations with skewed sex ratios?
effective size falls off rapidly
what does drift reduce?
genetic variation as result of extinction of alleles
small populations lose genetic diversity rapidly, which has 2 consequences
- populations may lose ability to respond to changing environment
- loss of alleles entails increase in homozygosity
difference between genetic flow and drift
flow: genetic migration, mixing of genes
drift: change in existing allele frequency due to random, reduced genetic diversity due to alleles being lost or fixed
Mating systems
- random (HWE)
- inbreeding (bw biological relatives)
- assortative (preferential b/w phenotypically similar)
- disassortive (pref b/w phenotypically different)