Exam 3

Question 1

What is selection?

Answer 1

heritable differences in fitness/phenotypes between genotypes in their fitness

Question 2

How long until fixation happens?

Answer 2

• higher selection=faster fixation
• when no directional selection ONLY drift, population size determines the rate because small populations more EASILY lose variation faster (think about probability, more likely to get equal numbers of heads and tails in 100 rounds vs only 10)

-important to remember that directional selection overcomes genetic drift in LARGE populations and when favored allele has high initial frequency

Question 3

If genetic drift AND directional selection are present in a population which will win?

Answer 3

Directional selection will overcome G.D. in large populations + when favored allele is already @ high frequency, ineffective in small populations

Question 4

What is heritability (h^2)?

Answer 4

indicates fraction of population that is due to GENETICS
-all environment: h^2=0

-all genetic: h^2=1
tells us how much variation is available for selection

Question 5

What is response to selection?

Answer 5

Response to selection=heritability x strength of selection
r=h^2 x s

r= response to selection (mean of offspring generation-mean of parental generation)
s= strength of selection (mean of reproducing individuals - mean of whole population)

Question 6

What are the ways that selection can act on traits/phenotypes?

Answer 6

1. Directional: one extreme favored
2. Stabilizing: Average values are favored
3. Disruptive: both extremes are favored

Question 7

Is stabilizing selection the same as overdominant selection?

Answer 7

NO!! Overdominant selection favors heterozygous GENOTYPES and tends to MAINTAIN allelic variation at ONE locus, while stabilizing selection favors PHENOTYPES near the mean and tends to REMOVE allelic variation @ MANY LOCI

Question 8

What is disruptive selection?

Answer 8

favors phenotype near both extremes, increase variance/standard deviation of trait, tends to MAINTAIN allelic variation

Question 9

What is stabilizing selection?

Answer 9

favors phenotypes near the mean, tends to remove allelic variation @ many loci, variance decreases, powerful agent of conservation

Question 10

What is directional selection? (graph)

Answer 10

one extreme favored, population mean moves, variance decreases, favored allele fixed

Question 11

What happens if variance/spread/standard deviation increases/decreases?

Answer 11

heritability (h^2) has direct relationship, so if variance decreases so does heritability

Question 12

What is a QTL (Quantitative Trait Loci)?

Answer 12

can identify genomic regions that affect trait, can be identified by correlating genotype with phenotype, with divergent lines,

Steps:create F2 generation and score individual for trait of interest and genetic markers that differ, if all alleles point in same direction=directional selection constant in past, however if alleles point in dif direction means that selective pressure has changed and favored different alleles in the past

Question 13

How do complex traits evolve?

Answer 13

positive selection acts over LONG periods to help mutant alleles @ many loci increase in freq and go to fixation, can cause sustained long term changes in trait value, selection acts on MANY loci and MANY alleles some directly others indirectly

Question 14

What is quantitative genetics?

Answer 14

utilize mean values of traits in populations, models how individual phenotype responds to selection when trait controlled by many alleles @ many loci

Question 15

What is broad-sense heritability?

Answer 15

ratio of total genetic variance to total phenotypic variance

measures proportion of phenotypic variance that has genetic basis; measure of how much variation in a trait in a certain population is explained by genetics
-if all environment: H^2=-0
-if all genetic:H^2=1
-H^2= Vg/Vp=Vg/(Vg+Ve)
Variation measured by V variance
Variance: sum of squared digs between each organisms trait value and population mean

Question 16

What is narrow-sense heritability?

Answer 16

h^2, measures proportion of phenotypic variance that has genetic basis and is in a form that selection can act upon; MEANING selection can CHANGE distribution of continous traits in a population (shift the bell curve, repose to directional selection), , estimate specific to population and environment being analyzed,

h^2=Va/Vp=Va/(Ve+Va+Vp+Vi)
*narrow-sense heritability can be estimated from parent–offspring regression

Question 17

Why is having a genetic cause not enough to explain variation in traits/phenotypes?

Answer 17

not all genetic effects accesible to selection, dominance relations among alleles and epistatic interactions among loci are not available for selection to act upon over generations, therefore, Vg broken down into 3 components:

1. Va=variance available to selection in long run
2. Vo= present variance due to dominance interactions
3. Vi=present variance due to epistatic interactions

Question 18

What is a parent-offspring regression?

Answer 18

gives narrow-sense heritability, lo and hi heritability estimated from regression of offspring phenotypic values vs avg of parental phenotype; MOST traits have non-zero heritability including human behavior
ex: human height has heritability of 0.6-0.8

Question 19

What are the 3 important points of heritability?

Answer 19

1. Heritability estimates apply to specific population and behavior
2. Heritability is a population, not an individual parameter
3. Heritability does not indicate the degree to which a trait is genetic, rather it measures the proportion of phenotypic variance that is a result of genetic factors

Question 20

What is the Breeders equation

Answer 20

used to predict change in a trait (R) based on the estimate of the selection differential (S) and heritability of trait (h^2); all complexities of multi-locus inheritance distilled into h^2, assumes that trait of interest NOT correlated with other traits having casual effects on fitness

Response to selection (R)= h^2*s (strength of selection)

Strength of selection (s)=mean trait value of reproducing individuals- value of whole population
Response to selection (R)= mean value of offspring generation- mean value of parental generation

Question 21

What is the process of adaptation?

Answer 21

Process: selection w/in population resulting in higher avg fitness and/or better fit to the environment
State: refers to actual trait itself, trait fulfills particular function=current utility, trait evolved to fulfill a particular function or=historical genesis, trait fulfills particular purpose and original evolved to fufill that function

Question 22

How do we recognize adaptations?

Answer 22

1. Observe or describe some organism trait
2. Formulate adaptive hypothesis for evolution of that trait
3. Test hypothesis by experiment

Question 23

Does trait have current utility?

Answer 23

does trait provide fitness advantage relative to hypothetical of not having trait

Question 24

Case Study #1: Ox and Oxpecker

Answer 24

believed that relationship was mutualism, ox provides bird protection while bird eats harmful ticks in ox’s fur, however, this is not the case. Attracting oxpeckers does not confer an advantage to ox bc they pick @ wounds,

conclusion:therefore relationship is NOT adaptive bc does not lead to higher avg fitness and NOT a mutualistic relationship.

Question 25

What is coevolution?

Answer 25

reciprocal selection, drives evolutionary arms race,
ex:Stickleback and tapeworms, tapeworm HAS to infect stickleback to complete lifecycle (obligate host), “common garden experiment” preformed so all difs in infection rate must be due to genetics, results: worms only viable in local host species and NOT foreign species=means evolved together

Question 26

What is GWAS?

Answer 26

genome-wide association mapping avoids need to create F2s and F1s (unlike QTL’s) and looks for associations between genetic markers and phenotypes; under assumption of random mating/can be confounded by population structure, does not use parent-offspring structure (unlike QTLs)

Question 27

Case Study #2: Nectar Guides, Does having nectar guides increase avg fitness

Answer 27

Study about attraction of nectar guides of pollinating flies, from study found that there was no change in fly approach-visitation rate however export to other pollen plants increased in flowers with nectar guides

Conclusion:Therefore strong selective pressure for nectar guides

Question 28

Case Study #3 Tephritid Fly

Answer 28

Fly have distinctive dark-wing bands and wing waving behavior (2 observed traits), hypothesis: markings and behavior mimics jumping spider thus deterring other predators or behavior specific to avoiding jumping spider predation
In order to determine why trait evolved in 1st place:
see if selective regime was in effect when trait evolved would be one in which it would have been advantageous, if an adaptation wing waving trait would have occurred AFTER spider predation while if an exaptation, wing waving occurred BEFORE spider predation

Conclusion: Flys mimic jumping spider behavior to avoid predation by jumping spiders

Question 29

Case Study #4 Horned Lizards

Answer 29

seemed natural selection occurring by birds which favored smaller horns making larger horns advantageous.

Evaluate 3 claims
1. The horns of horned lizards are under positive selection for the function of protection against shrike predation
Yes.
“predation by loggerhead shrikes generated selection that favored longer parietal and squamosal horns”, “both traits experience positive directional selection” (original article)
2. The length of horns is increasing in the studied population and will probably be longer some generations in the future
Yes.
“selection by shrikes generates the relationship necessary to continue to drive the elongation of horns in the short term” (response to response)
“These magnitudes of selection are less than the median observed in most selection studies but nonetheless indicate that constant selection with moderate heritability (0.5) of horn length would change squamosal and parietal horn lengths to a full standard deviation in 21 and 36 generations, respectively.” (original article)
3. The horns deserve to be called adaptations, with function of protecting lizards from shrike protection
No.
“even if the current functional role of a trait is known, the question of the origin of this trait remains unanswered” (response)

Question 30

Correlated Evolution

Answer 30

when characters evolved together, these characters can no longer be studied independently, can point to adaptation
Dif from coevolution (2 species) while correlated evolution is 2 characters in an individual

Question 31

What are the possible causes of trait correlation?

Answer 31

1. Developmental: when 1 trait evolves (might be due to selection) other also arises due to nature of development and physiology
2. Adaptation:when 1 trait evolves it imposes selection favoring changes in other trait

Question 32

How to evaluate adaptations w/ comparative approach

Answer 32

Need to check that correlation is not just a phylogenetic artifact/due to phylogeny, phylogenies generate an underlying covariance structure, can then use independent contrasts to correct for phylogenetic artifacts since traits show non-independence, branch lengths help determine ancestral trait

Question 33

What is independent contrast?

Answer 33

average the differences between taxa to estimate rate of character change across each node

Question 34

What is multilevel selection?

Answer 34

selection can act simultaneously on multiple levels of bio composition including cells and/or groups, not just on individuals/populations

Question 35

What are the 3 main ways that multilevel selection can occur?

Answer 35

1. Cytoplasmic selection: mitochondrial mutations
2. Somatic selection: cancer or selfish germ-line mutation
3. Gene selection: segregation distortion

Question 36

What is an example of cytoplasmic selection (cellular level)?

Answer 36

Mitochondrial mutations, organelle genomes inherited differently (maternal) vs nuclear, organelles w/in cell replicate independently thus can evolve, mitochondria can contain large deletions loosing ability to respire which is fatal in most eukaryotes

Experiment: Not fatal in yeast but provides disadvantage, but parasitic mitochondria proliferate due to increases replication, so w/in cell selection favors parasitic but w/in yeast selection favors respiration (functional mitochondria) therefore outcome depends on S (population size)

Outcome: when selection among yeast cells is weak, selection among mitochondria w/in cells can lead to fixation of trait despite decreasing overall fitness, this can be mistaken that lack of respiration is adaptive in small populations (when it isn’t)

Question 37

What is an example of somatic selection?

Answer 37

quantitative measure of impact of mutated genes on tumor fitness, mutations on somatic (body) cells and effect on fitness, mutations accumulate with age
ex: cancer and Apert syndrome (selfish germ-line mutation, favor germ cells carrying mutation and skews mutational profile of sperm as men age)

Question 38

What is an example of gene selection?

Answer 38

when genotypes deviate from expected Mendelian ratios, alleles that can get into more than 50% of the gametes of a heterozygote have an advantage

ex:Medea gene (artificial gene made in drosophila), mosquitoes with gene (M/+ or M/M) live (mother does not kill offspring) mosquitos without are killed (Mother kills offspring). The allele M rises to an unnaturally high frequency in the population. Having gene lowers fitness but it increases in frequency in the population

Therefore: selective advantage not due to individual carrying gene but gene itself

Question 39

What is meiotic drive (gene selection)?

Answer 39

selfish genetic elements that bias transmission (1 or more alleles) into gametes, often at detriment of rest of genome, usually sex-specific

Question 40

What are transposable elements (gene selection)?

Answer 40

• piece of DNA that move or copy themselves
• can cause mutations when insert or excise DNA segments which generally lowers fitness (i.e. selection favors TEs that avoid inserting into important genes, heterochromatin)
• can spread even if lower fitness
• TE’s incur cost by adding extra DNA to replicate which results in Genomic conflict so larger pop size= more effective individual selection can keep in tract
• also why genome sizes vary so much (esp in plants)
• can be BENEFICAL as promote gene duplication/reetrogenes which may aquire new functions
• while selection @ level of hosts may select against mobile elemnt, selection @ level of element themselves favor their spread (even if decreases fitness or reperoduction, extra copies of mobile element now present in gene pool can make up for it)
• therefore elements that replicate most efficiently and have least fitness costs to host are favored by natural selection and tend to spread
• @ least 45% of human genome is of active or former TE’s

Question 41

What is the “escaped” Te’s hypothesis in regards to viruses?

Answer 41

retroviruses could be escaped retrotransposons which happened to catch proteins that allowed infection of other cells

Question 42

What is an exaptation?

Answer 42

provide current function that did not evolve for such purpose
ex: feathers evolved before flight in dinosaurs, believed feathers used for thermoregulation however we now associate feathers with flight

Question 43

What is a quantitative trait?

Answer 43

A quantitative trait is a measurable phenotype that depends on the cumulative actions of many genes and the environment. These traits can vary among individuals, over a range, to produce a continuous distribution of phenotypes. Examples include height, weight and blood pressure.