Exan 3 Flashcards
What is effective size?
The size of an idealized population ( no migration, mutation, assortive mating, or natural selection) that loses heterozygosity due to drift at the same rate of as the population under study.
How does genetic drift cause heterozygosity to decrease over time?
- When alleles are fixed, variation is lost.
- Finite populations can be though of like inbreeding because in a finite population there is a nonzero chance that individuals mate with genetic relatives.
Genetic drift increase or decrease variation within population?
Decreases
Genetic drift increases or deceases variation between populations?
Increases
What are the 3 general consequences of genetic drift?
- In a finite population, allele frequencies fluctuate over time, even in the absence of natural selection.
- Over time, some alleles are fixed and others lost.
- Separate populations diverge in their allele frequencies and in terms of which alleles are present.
What is the model similar to hardy-weinberg model that uses small population? What the difference?
Wright-fisher model. Same assumptions but randomness in the pairing pooled gametes for a small number of individuals in
the population allows for change in the allele frequency from generation to generation
What are the 5 factors of H-W equilibrium?
Genetic changes - mutation
• Finite populations - genetic drift,
• Non-random mating – inbreeding
• Exchange of alleles among populations - migration
• Natural selection for or against certain alleles
If drift is the only evolutionary process, will finite populations become fixed or not?
Population size does affect the rate at which alleles get fixed and given enough time they will become fixed.
Can drift lead to divergence among populations?
Yes, differences in alleles frequencies and ultimately the fixation of alleles will led to divergence.
What is the probability that an allele at neutral locus will be fixed ?
The probability is equal to the frequency of that allele in the population at the time.
p=0.5 vs p = 0.75
What kind of wobble will we see for a population size of 10?
Large wobbles, less consitant
What kind of wobble will we see for population of 100?
Medium wobble, more consistent
What kind of wobble will we see for a population of 1000?
Small wobbles, most consistent
What happens to heterozygosity over time?
It decreases
Why does heterozygosity decrease over time?
Alleles going to fixation naturally reduce the diversity of alleles in the population and without allelic diversity, heterozygosity must
decline.
What is the average loss of heterozygosity in Wright-Fisher population?
1/2 N, N is equal to the population size.
In large population 1/2 N is small number for loss of heterozygosity. What would be expected for small population?
In small populations, 1/2 N is large and heterozygosity will decline quickly as result of drift.
Is census size always the same as re population size?
Rate of genetic drift (the rate of the loss of heterozygosity) is not
really proportional to the census population size .
What deviations will cause effective population size to differ from census population size?
There are equal numbers of males and females, all of
whom are able to reproduce.
• All individuals are equally likely to produce offspring,
and the number of offspring that each produces varies
no more than expected by chance.
• Mating is random.
• The number of breeding individuals is constant from
one generation to the next.
Can effective population size be impacted by different sex ratio?
Yes, predicted by formula
Ne = 4NmNf/(Nm + Nf)
What is a bottle neck?
refer to a brief period of
small population size.
What happens to the diversity of a population undergoing population bottleneck?
It reduces genetic diversity
and can accelerate
changes in allele
frequencies due to
genetic drift.
What happens to allele frequencies under a bottleneck? What about after?
Allele frequencies fluctuate much more under bottleneck more than before or after.
After bottleneck allele frequencies differ greatly from one population to the next.
What is the founder effect?
The founder effect refers to the change in allele frequencies
that results from the sampling effects that occur when a small
number of individuals from a large population colonize a new
area and found a new population.
How can founder genes differ from mainland population?
Genes in founders typically represent only a subset of genes
present in the mainland population.
Alleles that are extremely rare on the mainland may become
common on the island if carried by one of the founders of the
island population
What dominates in small population? Drift or selection
Drift
What dominates in large population? Drift or selection
Selection
How does population size affect the magnitude of allele frequency
changes due to drift?
Allele frequency changes due to drift are larger in smaller populations
On average, what effect does genetic drift have on the
heterozygosity of a population?
Genetic drift leads to a decrease in the
average heterozygosity of a population over
time.
On average, what effect does genetic drift have on differences
between populations?
Genetic drift will cause different alleles to go to fixation in different populations, thereby increasing
differences between populations
What is a population bottleneck, and how does it affect genetic
diversity?
A population bottleneck is a temporary decrease in
population size, usually with an abrupt onset. Bottlenecks decrease the amount of genetic variation in a population
In a leading edge expansion, individuals from a source population move out to
colonize a previous unoccupied region. When this happens, where is genetic diversity expected to be greatest?
In a leading edge expansion, we expect more genetic diversity in the original region of the source population than in the newly colonized region. This is because only a subset of the individuals in the original region—those along the leading edge—move into the newly colonized region
A researcher sets up 100 replicate population cages. Each is founded with 20 Drosophila melanogaster individuals, drawn from a population that is polymorphic for
the L1 and L2alleles at a neutral pseudogene locus L. After many months the L1 allele is fixed in 11 of the cages and the L2 allele is fixed in 89 of the cages. Estimate the frequencies of the L1 and L2 alleles in the original population from which these cages were founded.
The probability of fixation of a neutral locus is equal to its frequency in the
population. Thus, we can estimate that the original frequency of the L1 allele was around 11% and the L2 allele around 89%.
In many polygynous songbird species, such as wrens or red winged blackbirds, a single male holds a territory and mates with several females on that territory. In monogamous species, such as cardinals and blue jays, mated pairs typically hold a territory and males mate with only one female. In comparably sized populations, do you expect drift to have a stronger effect in polygynous species or monogamous species? Explain your choice.
In a monogamous species, most individuals reproduce in approximately equal numbers, so the effective population size is close to the census population size. In a polygynous species, some males have a large number of offspring while others have few or none. Because some males don’t reproduce at all, this is like having a smaller population, with a skewed sex ratio. Thus, in a polygynous species the effective population size will be smaller than the census population size. As a result, drift operates more strongly in a polygynous species than in a monogamous species of
comparable size.
Discrete traits which are determined by a single gene are the minority in nature. T or F
T
What do you call traits that are determined by the effects of multiple genes?
Polygenic
What kind of variation is shown when traits are determined by many genes?(Polygenic traits)
Continuous variation
What type of gene effect is obtained by summing the effects of individual alleles?
Additive genetic effect
What are characters with continuously distributed phenotypes are called?
Quantitative traits
What is latent variation?
New types or values of traits not seen in a parent population could appear in
offspring produced by that population.
Why are latent variation important?
They can introduce more variation if a population faces natural selection since the traits have been present all along. It can restore variation.
Sometimes genes do not interact additively but in many cases genes interact with each other non additively called?
Epistasis
Besides genes what is the second thing to influence phenotype?
Environment
How do measure heritability variation?
P=G+E
G=genotype
E= environment
P=phenotype (individual)
What measures how different individuals are from the mean and the spread of the data? (Measuring heritable variation)
Varience
What is varience?
Varance is the average squared dev1at1on from the mean. Standard deviation is the square root of the variance.
What is broad sense heritability?
It defined the fraction of total variance that is due to genetic causes.
What is the heritability value range?
Between 0 and 1 (fraction)
How can narrow sense heritability be measure?
Parent offspring regression
Selection experiments
What is breeder’s equation?
R=h2S
Or
H2=R/S
R=selection response
S=selection differential
H2= narrow sense heritability
Narrow sense heritability is defined as the total:
Additive genetic variation divided by the total phenotypic variation
What is truncation selection?
The individuals in a given generation are pooled, a sample is measured, and only those individuals above (or below) a given phenotypic value (truncation point) are chosen as parents for the next generation.
How does heritability change over time?
Selection removes additive genetic variance from a population over time.
What concept regarding heritability is revealed for the fact that heritability changes over time?
• Heritability is a statistical property of a population, not a general fact about the genetic basis of a phenotypic trait.
• Heritabilities are within-population measures, not between population measures - that is, heritability tells us about the sources of differences within a population, but not about the sources of differences between populations
T or F
If a person has [the genes] for a disorder that has a heritability of
1, then the person will suffer from the disorder.
False
T or F
The heritability of having fingers on each hand is 1 or close to 1.
False
T OR F
Heritability and inherited are nearly the opposite in meaning.
TRUE
T OR F
The heritability for wearing neckties is high.
True
T or F
The heritability for traits found in identical twins is 1.
False
T OR F
As the environment gets more similar for individuals of very
different heritabilities, heritability increases.
True
T OR F
The heritability of a group of individuals with relatively similar
heredities in very different environments is relatively
low.
True
What does extinction mean?
It means that all individuals in that species have died out and left no living descendants
T Or F
Most species that have ever lived have gone extinct.
True
Can fossils have skin?
Yes, well preserved ones can have skin tissue
What are the types of fossils that can be found?
Can be original skeleton or
shell (or skin!)
Can be material that replaced
once living thing
Can be a mold or cast
Can be traces such as
footprints or burrows
What can fossils tell us about the environment organism lived in?
– Analyses of oxygen content
– Acidity
– Co-occurring species
Are complete fossils common?
No, they are rare. Most are partial fossils. Complete fossil are rarest in the oldest rocks.
What are conditions for fossilization?
Organism must be buried and the remains must remain in an anoxic (oxygen-free) state
– Vast majority occurs in sedimentary rock
– Must not be disturbed by predators and scavengers
– Finally, must be exposed by the process of erosion and eventually discovered
What’s the criteria paleontologist use when choosing sites?
– Focus on sites that best match geologic and abiotic conditions in which fossilization occurred
– Begin near sites where others have uncovered related fossils
– Phylogenetic reconstruction may guide paleontologists to a specific area
How do you date fossils?
The observation that fossils found lower down in the sediment at a
particular locality are older than those found closer to the surface.
– Radiocarbon dating and radioisotope dating
What is radiocarbon dating and radioisotopes?
Different isotopes have different resolutions.
– Carbon-14 has a half life of 5730 years. It will decay into a
second form of Carbon – carbon-12. The 14C/12C ratio can be
used to measure absolute time for about 50,000 to 75,000
years
– Potassium-40 has a half life of 1.3 billion years
– It decays into Argon-40,
– Most ancient fossils dated by Potassium-Argon dating
How else do you date a fossil?
Paleomagnetic dating
• The polarity of the earth’s magnetic field has changed back and forth on numerous occasions
• By measuring alignment of metal particles in the substrate in which the fossil was found, paleontologists
can estimate a relative date for an associated fossil
What is backward-smearing?
The last fossilized sample of a species that can be recovered is rarely, if ever, the last true survivor of a species that has gone extinct. Backward-smearing effects make us date an extinction earlier than it actually occurred. Time lag between last known fossil
and actual extinction is called the Signor-Lipps effect
What is the time lag between last known fossil
and actual extinction called?
Signor-Lipps effect
What is forward smearing?
Burrowing animals move fossilized remains up through layers of earth and distort the fossil record. A species that is actually extinct still shows fossilized remains well after it’s extinction.
What is background extinction?
When extinction occurs outside a period of mass extinction.
Within all extinctions, what percent are background extinction?
95%
What is mass extinction?
The rates of extinction vary over time and extinction rates sometimes spike. These spikes are referred to as mass extinctions
How many mass extinction have happened?
5 to 8 mass extinctions
What are the main 5 mass extinctions?
Oldest: Ordovician (445ish mya)
Devonan (400 mya)
Permian (250 mya)
Triassic (230 mya)
Recent: Cretaceous (100 mya)
What are the risk factors for background extinction?
Here we focus on factors that affect
contemporary extinctions.
– Species that are endemic, native to only one area, are especially prone to extinctions.
– Thus, having a broad geographic range, can act as a buffer against risk factors such as predation,
competition, disease.
What are direct effects of extinction and predation?
Many islands represent areas where eventual prey species
have evolved in the absence of predators. An example is the
Channel Islands off of California . The extinction of the Guadalupe-storm petral has been attributed to predation by feral cats.
• Black-vented shearwaters, Cassin’s auklets, and Xantus murrelets have all experienced dramatic population
declines since the introduction of feral cats.
What are the indirect effects of extinction and predation?
The introduction of pigs on Santa Cruz island led to a series of trophic interactions that led to the near-extinction of channel island foxes.
Pis attracted eagles which also eat foxes (skunk pop decreased). Foxes kept skunks in check but since they were eaten, skunk pop increased.
Again what are the big mass extinction?
1) Mid-Ordovician
• 2) The Late Devonian
• 3) Permian
• 4) Late Triassic
• 5) Cretaceous-Tertiary
What happens to survival rate for survivor post- extinction? Compared to pre-extinction.
Survival rate tend to be lower than pre-extinction.
What is “dead clade walking”?
to describe clades that survived a period of mass extinction, only to go extinct in the next geologic time period
In addition to taxonomic diversity (number surviving species), extinction also lowers
diversity with respect to?
– Morphology (form and structure)
– Behavior
– Niche occupation
– Developmental patterns
Mass extinction lead for what type of opportunity afterwards?
Adaptive radiation. Organism diversity rapidly after a mass extinction.
The death of dinos leas to what type of radiation?
Radiation of mammals
followed.
• Best-studied and most
famous mass extinction
What is the K-T extinction?
A meteorite big enough to be
called a small asteroid hit the earth
at the time of the K-T extinction.
What was found in rocks K-Pg boundary?
They found that the rocks laid
down at the K-Pg boundary contain
very high concentrations of iridium
(a very rare naturally occurring
element).
• The same ratio of iridium is found
on comets, meteorites, and
asteroids.
Where is iridium found?
Can be found scattered around the world in the same level of rock layer.
What is found at K-T boundary as well as other extraterrestrial impacts?
Spinels (glassy minerals)
Impact diamonds
Extraterrestrial amino acids
Where is the crater from the K-T extinction?
Yucatan peninsula
What is the largest mass extinction?
Late Permian mass extinction.
Largest mass extinction on record. 90% of aquatic and 70% of terrestrial species went extince. 60% of animal families were eliminated.
What happened to ocean organisms during late Permian mass extinction?
In the ocean, certain groups of plankton, nearly all organisms associated with reefs, and many fish, shellfish, and bivalves all became extinct.
What happened to land organisms during late Permian mass extinction?
On land, large extinctions took place among amphibians and reptiles, arthropods, and woody plants
What adaptation increased the surface of organism in late Permian mass extinction?
Individuals adapted to low oxygen levels were more likely to survive the Permian mass extinction
What likely caused the late Permian mass extinction?
At the Permian-Triassic boundary, there were a series of huge
volcanic eruptions in the Siberian traps.
• Brief period of global cooling caused by debris
• Global heating followed (temperature increase of 6 degrees C).
Huge amounts of carbon dioxide released by volcanoes.
• Likely an increase in ocean acidity.
An ongoing debate in the study of paleontology is whether macroevolutionary patterns are natural extensions of microevolutionary processes. Or if separate macroevolutionary processes are at
work. What are examples?
For example, one could claim that species that have existed for a long time are less likely to go
extinct.
• Alternatively, life history properties of a species could also affect the probability of extinction.
What are the types of survivorship?
Type 2
In type 1: there is high survivorship in early and middle life, followed by a rapid decline in survivorship.
In type 2: The probability of survival is constant with age.
In type 3: Very high mortality early, with relatively low rates of death for those surviving bottleneck.
Which type of survivalship follows extinction most closely?
Van Valen found species
longevity had no effect on the
probabillity of extinction.
How well a species in a taxon
had adapted in the past was
irrelevant to the probability of
extinction in the future.
Another ongoing debate is about whether one ought to take the fossil record at “face value” or infer gradual change that is missing due to the incomplete nature of fossilization. What are the two views?
Gradualism: morphological change can occur without speciation.
Stasis+ punctuation: morphological change only occurs during speciation
There is evidence for both.
Cladogenesis?
New forms appear in fossil record through branching speciation events
What is Anagenesis?
Anagenesis is the gradual evolution of a species that continues to exist as an interbreeding population
