Chapter 17: Microevolution Flashcards
1
Q
microevolution
A
involves looking at changes in the genetic make-up (genotype) of population of a species over time
2
Q
factors that affect genetic make-up generation to generation // 4 agents of microevolution
A
- gene flow: introduces new alleles to populations
- genetic drift: reduces genetic variability within populations
- mutation: random and create genetic novelty (new alleles can even arise in the population)
- natural selection: shapes genetic variability by favouring some traits over others
honorary: non-random mating
3
Q
humpback whales
A
- example of genetic drift: BOTTLENECK
- Arabian Sea population doesn’t migrate, and is separated from other populations
BOTTLENECK:
- bottleneck (hunting pressure) - prone to inbreeding
- decreased genetic variation
- causes inbreeding pressures (increased risk of extinction and decreased fitness)
4
Q
the evolution of humpback is an example of…
A
microevolution- change in the genetic makeup of a population from one generation to the next
5
Q
phenotypic and quantitative variation
not related
A
phenotypic- heritable differences in appearance or function (behaviour + physiology)
phenotypic plasticity
quantitative- individuals differ into small, incremental ways
6
Q
Qualitative variation and Polymorphisms
interconnected
A
Qualitative variation- characters with discrete states
polymorphism- discrete variants of character//difference in nucleotide sequence of a given gene in a different individuals of a species (gene occurs in different forms in the population)
CERTAIN GENES DRIVE CERTAIN PHENOTYPE
we can describe the phenotypic polymorphisms quantitatively by calculating the frequency of each trait
7
Q
T/F: genetic and phenotypic variations may not be perfectly correlated
A
T:
REASONING
- only genetic differences in phenotype is heritable
- organisms with different genotypes can exhibit the same phenotype (AA or Aa)
- organisms with the same genotype can exhibit different phenotypes (i.e. the acidity of soil influences the colour of hydrangeas; same seed=same genetics, but different environment=diff levels of pH in soil to create a diff phenotype [PHENOTYPIC PLASTICITY]
8
Q
Why is it important to know whether phenotypic variation is caused by genetic differences, environmental, or an interaction of both
A
- only genetically based variation is inherited and thus subject to evolutionary change
- knowing the causes of phenotypic variation has important and practical applications
I.E. wheat production
Field A produces more grain than Field B, a farmer would want to know if it was because of differences in availability to nutrients or water to replicate equivalent tx to Field B.
However, if it was because of genetics, then the farmer would only plant Field A because it’s the more productive genotype.
9
Q
An organisms phenotype is frequently…
A
the product of an interaction between genotype and environment
10
Q
How can we determine if environment or genetics contributes to differences in phenotype
A
- we can test for an environmental cause experimentally by changing one environmental variable and measuring the effects on genetically similar subjects. [GENETICS CONSTANT, VARY ENVIRONMENT]
(plants of the same genotype that are grown in full sunlight tend to have smaller leaves + shorter stems than plants in the shade - breeding experiments [MENDEL] can demonstrate the genetic basis of phenotypic variation
11
Q
are breeding experiments practical
A
not always, particularly for organisms with long generation times which can raise ethical concerns (esp for humans)
12
Q
phenotypic plasticity
A
when same genotype in a different environment leads to different phenotypes
+
the ability of an organism to change its physical characteristics, behavior, and physiology in response to its environment
13
Q
genes & polymorphism
A
genes can create POLYMORPHISM
- same genes can create different colours for ex.
14
Q
qualitative variation and Gaussian distribution
A
Broad low curve: indicates a lot of variation among individuals
High, narrow curve: little variation among individuals
=a decreased change in the environment generally creates narrower selection pressure because stable conditions reduce the need for adaptation, favoring traits that are already well-suited to the environment.
15
Q
Alternate Reproductive Tactics
A
- polymorphisms can generate equal fitness amongst individuals in a population with alternate reproductive tactics
FISH EXAMPLE:
- bigger male fish physically compete for females
- smaller fish mimic the appearance of females so they can sneak their sperm in female for fertilization
RISK: if the smaller one is caught by the bigger one, the bigger one will kill it
16
Q
Hardy-Weinberg principle
A
- null hypothesis that defines a population NOT evolving
conditions where diploid organisms have GENETIC EQUILIBRIUM (no evolution)
- if conditions met [accept H/W], microevolution doesn’t occur
- if observations don’t match null [don’t follow H/W], microevolution occuring
- mechanism for persistence of recessive alleles
if we reject H/W and say the population is evolving, we still don’t know the mechanism its evolving w/
17
Q
population genetics
A
- focuses on genetic variation that exists within a population and how this changes over time via evolution
- population geneticists first describe the genetic structure of a population, they create and test hypothesis formalized in mathematics to describe evolution in specified conditions
18
Q
evolution can be caused by 4 distinct pressures
A
1) mutation
2) genetic drift
3) gene flow
4) natural selection
= can work alone or in combination with each other
19
Q
trait
A
inherited characteristic of an individual related to their appearance, abilities, and behaviours
20
Q
genetic variation is caused by
A
individuals possessing different versions of the same genes
- different individuals may carry different alleles for one or more genes
- gene can have several different alleles
21
Q
locus
A
location of a gene on a chromosome
22
Q
evolution
A
change in allele frequencies from 1 generation to the next. Changing how common a particular allele is within a population (its frequency) changes genetic makeup of a population
23
Q
gene pool
A
the total genetic variability of a population is represented by all the alleles at all the gene loci in all individuals within the population and referred to as the GENE POOL
- can also refer to frequency of the axles of one locus within the population
EXAMPLE:
- total of all alleles for fur colour in individuals in a mice population is the gene pool for this particular locus
24
Q
the amino acids sequences among different species are..
A
- SIMILAR BUT NOT IDENTICAL
- differences in the amino acid sequences of a protein reflect changes in the gene sequence; and even within individuals of the same species, gene sequences are often different
25
both protein-coding and non-coding regions of DNA
harbour genetic variation
26
study of single-nucleotide polymorphism (SNPs)
- single-nucleotide differences can exist btwn individuals and have been shown to account for about 90% of the genetic variation found in humans
27
genetic variation has 2 potential sources
1) the production of new alleles [via migration: new species bring new alleles with them and via mutations for ex]
2) rearrangement of existing alleles into new combinations
- new alleles arise from processes that introduce changes to the actual DNA sequence
- genetic variation can come about by changing the arrangement of alleles along a chromosome
- caused by genetic recombination during meiosis
- shuffling of alleles into new combinations can produce an extraordinary umber of new genotypes in the next generation
28
genotypes are individual-specific
extremely unlikely that another person with your genotype has ever liked or ever will
29
traits are the
- product of many genes
- traits are strongly influences by the environment
this is why population geneticists chose systems to study where a clearly identifiable heritable trait was controlled by a single gene (i.e. flower colour in snapdragons is controlled by a single gene)
30
genotype and allele frequency
genotype: percentages of inidivudlas possessing genotype
allele: calcualtde from genotype in diploid organisms
*p and q: 2 diff alleles at a locus*
= represents the f of those 2 diff alleles
31
Example of genotype + allele frequency
Aa
- each a (A and a) is a genotype f
- the whole thing (Aa) is an allele f
32
Hardy-Weinberg Conditions
1) no mutations occuring
2) population closed to migration (if individuals are migrating into population, they bring new alleles with them)
3) population infinite in size
4) all genotypes free of selection (no natural/sexual selection)
5) random mating with respect to genotype (No inbreeding)
33
null hypothesis
conceptual models that serve as theoretical reference points to observation
(used as H/W benchmark)
34
genetic equilibrium
allele frequency and genotype frequencies don't change from one generation to the next
35
agents of microevolution
- populations allele frequencies will change over time if 1+ of the 5 conditions are violated
36
gene flow introduces new alleles into populations
- the allele and genotype frequencies of a population can change due to migration into or out of the population
- sometimes their gametes (like flower pollen) can move from one population to another and may introduce novel alleles into a population shifting allele and genotype frequencies away from the values predicted by H/W model
37
gene flow and H/W
violated H/W model that populations must be closed to migration
38
examples gene flow
- young male baboons typically move from one local population to another after experiencing aggressive behaviour older males
- marine invertebrates disperse long distances as larvae carried by ocean currents
39
population
group of interbreeding individuals and their offspring
40
if you go through hardy Weinberg and there are no changes then...
you are in genetic equilibrium, no evolution
41
1 cycle of a generation of h/w
gametes to adults
42
Simulation of H/W
- track fate across generations of genes
- the A locus
- 2 alleles: A and a
- need to know the gametes produced by the adults when they mate
- each parent carries either A or a
- meiosis with egg and sperm
- each gamete gets one copy of allele A (i.e. 60% A and 40% a, yields A(0.6) and a(0.4))
Example: mixing fish sperm and eggs (random fusion)
- assume adults choose mates randomly
- not typical in the wild (due to sexual selection and preferences)
NO CHANGE= no microevolution, yes h/w
CHANGE= yes microevolution, no h/w
43
Luck-Free results
- random chance (genetic drift) does not affect allele frequencies
44
H/W and probability
- random mating in the gene pool produces zygotes in the following proportions
A= 0.35
A=0.48
aa=0.16
=1
- Łęt zygotes grow to adulthood and then they will make gametes to make the next gene pool
*if chance plays no role then the exact same ratios will come into play= genetic equilibrium, H/W is satisfied*
45
when organisms exit equilibrium, how do they do it?
through agents of microevolution
46
codominant alleles and hardy Weinberg yield the following possible diploids
A1A1
A1A2
A2A2
47
Steps of hardy Weinberg
let p= frequency of A1
let q= frequency of A2
thus, p+q=1 (only 2 alleles)
STEP 1: gametes combine to make zygotes
STEP 2: zygotes=genotypes among zygotes formed
STEP 3: adults-make gametes in the same frequency (if nothing impacts them, ratio will stay the same)
48
Fundamental conclusions of hardy-weinberg
1) allele frequency in a population won't change generation after generation
2) if allele frequency in a population is given by p and q, then genotype frequency will be given by: p^2, 2pq, q^2 (p^2+2pq+q^2 are the proportions)
49
Why use the H-W equilibrium
proof to show NO evolution has occurred
provides a NULL MODEL to compare results against (statically speaking...)
- alelle f to current frequency from sample of population
- test whether or not that population has undergone evolution
50
Assumtpions 1 of H/W
1) NO NS
- all individuals survive and equal rates
- individuals contribute equal number of gametes to the gene pool
- should also be 0 mortality difference
IF VIOLATED?
- when some individuals with some genotypes survive and reproduce better than others, allele frequency will change
example: predation
- violates assumption, creates a selection pressure and changes the preferred phenotype no genetic equilibrium
51
Assumption 2 of HW
2) NO MUTATION
- no copies of existing alleles were converted by mutation into copies of other existing alleles
- no new alleles were created
- small effect, only important in the long term
IF VIOLATED?
- some alleles have higher mutation rates than others, changing allele frequencies
(i.e., certain functional genes have higher mutations than others)
52
Assumption 3 of HW
3) NO MIGRATION
- no individuals move into or out of the population
- assume single isolated population with no gene flow
IF VIOLATED?
- individuals carrying some alleles move out of the population, at higher rates than individuals carrying other allies causing allele frequencies to change
53
Assumption 4 of HW
4) NO CHANCE EVENTS
- that cause individuals with some genotypes to pass more of their alleles to the next generation than others
i.e. blind luck plays no role
- avoided if population is infinitely large
IF VIOLATED?
- genetic drift, allele f will change
- forest fire kills 1/2 of the birds=genetic drift
- allele f will change as birds with specific alleles are dead
54
Assumption 5 of H/W
5) INDIVIDUALS CHOOSE THEIR MATES AT RANDOM
- gametes find each other randomly
IF VIOLATED?
- e.g. individuals prefer to mate with other individuals of the same genotype
result= no changes to allele frequency
but genotype frequency will change
- i.e. if I'm a A,A, dark male and **prefer** the same female
= ratio of allele frequency won't change
- packaging of alleles are skewed, and genotype frequency changes drastically (non-random mating)
= unmask bad recessive alleles so you're experiencing an increase in frequency of aa , these aa will die off more and this will change the genotype frequency
= 1 generation delay in terms of the effects of non-random mating
55
Non-random mating takes
2 generations to see the effects (which is why its treated as honorary)
56
GENE FLOW
- movement of alleles across different populations
- may occur from individuals or gametes
Life history/behaviour may enhance gene flow
- some individuals migrate (more gene flow) in the winter and some don't (no gene flow)
Dispersal agents (e.g. blue jays) can enhance gene flow
- take seeds to plants
- defacate a seed they've eaten somewhere else OR carry acorns from one population to another
- uneaten acorn can germinate and contribute to gene pool of population into which it was carried
57
gene flow + trees..
what can the trees be described as
- secile organisms (i.e. trees)
=non-moving
= require dispersal agents (trees adapted to use these to avoid interbreeding)
58
MIGRATION
**NOT THE SAME AS SEASONAL MOVEMENT**
- movement of alleles between populations
- not the same as seasonal movement of individuals
GENE FLOW: transfer of alleles from the gene pool of 1 population to the gene pool of another population
- mechanisms of gene flow: occasional long-distance migration of juveniles, spores spread by wind, etc.
- migration varies a lot depending on mobility of individuals and propagules (i..E number of acorns moving)
59
Adding migration to H/W
- one island model: simple model of migration
- 2 populations continent and small island offshore
HIGH IMPACT: continent sending alleles to island
LOW IMPACT: island sending alleles to continent
- island is small so any movement from island to continent does not affect allele or genotype frequencies (won't take it from h/w)
60
Case study: Water snakes
- individuals vary in appearance (unbounded/bounded)
- bands are determined by a single locus w/ 2 alleles
- banded allele is dominant over unbounded allele
---------------
mainland=banded (camouflaged)
island=unbanded (bc having bands makes u stick out, so they survive more)
- likely due to N.S. (predation)
BUT NOT ALL ISLAND SNAKES ARE UNBANDED BECAUSE OF MAINLAND SNAKE MIGRATION
- migrant snakes bring copies of banded alleles to gene pool
- migration is acting N.S.
- populations go in and out of equilibrium
- more variability
61
GENETIC DRIFT
genetic drift:
- random change in allele f
- most important in smaller populations
- reduces genetic variability
{VALID FOR SMALL POPULATIONS}
OUTCOME:
1) founder effect
- due to few individuals starting new populations
*missing many alleles from larger populations, population is currently small*
2) population bottleneck
- reduction in alleles due to population reduction (changes in environment/human activity)
- only few alleles make it *population goes from large to small*
62
Genetic drift leads to
- changes in allele frequencies
**NOT ADAPTATION
- random process (i.e. forest fires kills 90% of birds, assuming the 10% of survivors aren't variably different than the 90%
= random loss)
- drift results for violation of infinite population size assumption (population is small)
63
Loss of variability
- leads speaker to become inbred
- can lead to endangerment
64
summary of genetic drift
1) no adaptation
2) small population
3) either FOUNDER or BOTTLENECK
65
sampling error and evolution
= founder effect
- observing drift in nature amongst small populations which are usually founded by a few individuals are alleles are likely different from older, large population due to chance
- direct result of sampling error
= very important in conservation biology
## Footnote
sampling error occurs because the smaller population cannot perfectly reflect the original genetic variation, SOME ALLELES LOST DUE TO LUCK INSTEAD OF SELECTION
66
the amish and founder effect
- exceptionally high incidence rate of ellis-van creveld syndrome [genetic disorder leading to abnormal bone development]
- originally founded by a group of germans
- the amish only marry within their own community leading to a higher incidence of recessive disorders and inbreeding
67
bottleneck can cause
alleles that were rare in the OG population to be totally lost in the population
68
elephant seals and bottleneck
- hunters wiped out almost all elephant seals
- rebounded from 20 individuals to 160 000 today
- derived from a group of only 20 individuals, the original genetic diversity can never be regained and now there are far fewer alleles at any one locus in the gene pool
69
why is genetic drift so important for conservation biology
- they represent populations with few individuals and thus very little genetic diversity
- regardless of how large the population ends up, It will be based on a small gene pool
- endangered species can be protected but the lower genetic diversity leaves in more susceptible to disease and less capable to cope with environmental changes
= we need to protect them!
70
molecular evidence of founder effect
- small songbirds native to Australia and Tasmania migrated to new islands several time
BREAKDOWN OF MIGRATION
1) Tasmania + australian mainland
2) New Zealand south island
3) chatham island
4) Palmerston north
5) New Zealand north island/Auckland
6) Norfolk Island
= silvereye colonized new islands and a smaller and smaller group was moving every time
FOUNDER EFFECT PREDICTION: each new pop. will have a randomly chosen subset of alleles present in the go population [FOUNDERS]
- i..e 60 moves the first time, 16 the second, 5 the third, etc.=loss of alleles, you lose alleles whenever u make a new population
PREDICT: as birds went from island to Island, allele variation should decrease along the route
71
MUTATION
- change to the double strand sequence of DNA
- spontaneous heritable variation in DNA
- rare event, significant over long-time scales
- caused by radiation, hazardous chemicals, mostly normal cellular processes and mistakes (rarely:environmental factors)
*delterious mutations are harmful to organisms (i..e aa)*
72
TYPES OF MUTATIONS
1) point mutation: single nucleotide (base) is changed, also called substitution
2) insertion: 1+ nucleotide base pairs are introduced
3) deletion: 1+ nucleotide base pair is removed from a DNA sequence
4) inversion: a segment of DNA breaks and is inserted back into its original position in the reverse orientation
5) duplication: DNA is copied twice, the duplication can be part of a gene, a whole gene, or an entire genome
73
t/f: recombination results in mutation
F
- genetic recombination btwn homologous chromosomes can result in genetic variation but its very precise and generally won't result in mutation
74
4 KEY ASPECTS OF MUTATION
Source of Genetic Variation – Mutations create new alleles, increasing genetic diversity
.
Random Occurrence – Mutations happen by chance, not because organisms "need" them.
Effects Vary – Mutations can be beneficial, harmful, or neutral, depending on the environment.
Heritability – Only mutations in germ cells (sperm/egg) can be passed to offspring.
## Footnote
CHECK WITH UR NOTES!!!
75
TYPES OF NATURAL SELECTION
**MOST COMMON:**
DIRECTIONAL SELECTION: favours individuals near 1 end of phenotypic spectrum
i.e. bigger beaks = more fit
smaller beaks = more fit
= doesn't matter if its small/large as long as its in 1 direction {either extreme}
**2nd most common**
STABILIZING SELECTION: favours individuals with intermediate phenotypes (middle/average phenotype is more fit than 2 extreme)
**least common**
DISRUPTIVE SELECTION:
favours individuals with extreme phenotypes
(favours 2 extremes)
i.e. big/small salmon
= disruptive selection because they're both fit
EXAMPLE: the fish that sits by and mimics females to reproduce VS generally strong fish
76
STABILIZING SELECTON
- when population is well adapted
- avg phenotype is fit
= lose 2 extremes
- individuals with intermediate values of traits have highest fitness
- doesn't alter the trait in a population
- reduces number of individuals in the trails of the traits distribution (reducing variation)
77
DIRECTIONAL SELECTION
for mice: may have died due to predation, cant camouflage
- positioned to the right/left...
=idea that bigger/smaller is better
*fitness consistently increases (or decreases) with the value of a trait
*changes average value of trait in population
*reduces variation in a population (not dramatic)
*ornamentation in males
78
DISRUPTIVE SELECTION
- intermediates could have been killed by predators
- fitness peaks are on either extreme ends
- Individuals with extreme values of trait have the highest fitness
- doesn't alter the average value of the trait
- trims off the MIDDLE of the trait distribution increasing the variance
case studies: ground finches and lazuli buntings
79
Do Humans Experience Stabilizing selection
- premature babies and big babies
**strong selection against premature babies and big babies = pushing them out can kill the mom and itself [during birth]**
strong selection pressure=baby head size
80
disruptive selection: lazuli buntings and ground finches
GROUND FINCHES:
- selection favours extreme phenotypes
- birds with average beaks do bad
- birds with small and large do best
LAZULI BUNTINGS:
- dullest and brightest male birds were more successful in obtaining
1) pairing with females
2) siring offspring/helping to birth offspring via mating (compared to intermediate males who did bad)
81
value of mutations
- only microevolutionary process that gives rise of new/unique genetic variations/traits
*IT DOES NOT allow for rapid change to a population, and genetic drift/gene flow/and n.s. work faster*
82
effect of inbreeding on genotypes
- in extreme cases of inbreeding when the same genotype mate to make the next generation
- % of heterozygous will decline by 50% each generation whereas homozygotes will increase 25% each generation
- but, from one generation to the next allele frequency does not change
## Footnote
ONLY WAY.U CAN CHANGE ALLELE F IS BY ADDING/REMOVING ALLELES
83
interbreeding vs inbreeding
interbreeding-Refers to mating between individuals from different populations or species, leading to the mixing of genetic material
Inbreeding- Refers to mating between closely related individuals, which can increase the risk of genetic defects due to the increased chance of inheriting harmful recessive alleles.
84
non-random mating simulation
if they only mate w/ their own
AA x AA = all AA offspring
aa x aa = all aa offspring
Aa x Aa = AA (1/4), Aa (1/2) , aa (1/4)
- in the case of inbreeding, we produce 25% more aa= more common
- unmasking recessive alleles
= decreases fitness
= no change in allele frequency
= selection kills of aa
OVERALL:
- increase in homozygotes (aa and AA) and decrease in heterzyogtes (Aa)
- results in deviation from H/W (p^2+2pq+q^2)
-DOES NOT MEAN EVOLUTION OCCURRED BECAUSE ALLELE FREQUENCIES DID NOT CHANGE FROM GEN TO GEN
85
H/W and inbreeding on genotypes
- you need the allele frequencies + deviation from H/W to change in order to determine if something is evolving
= therefore, inbreeding does not cause evolution it just changes how genotypes are "packaged" into diploid zygotes (moves them from Aa to AA and aa)
- this can lead to inbreeding depression
86
inbreeding depression
- morę homozygotes than heterozygotes
- inbreeding depression= decrease in the average fitness of inbred individuals
i.e. inbred bird eggs don't hatch as often leading to an increased risk of morality
i.e. children of first cousins have disabilities and other problems
= bad recessive alleles are exposed
unfit traits are inherited
producing kids that are less fit
[ doesn't always lead to these issues but the risk is way higher]
87
how do we solve inbreeding
Outbreeding:
- bring alleles into population
genetic rescue:
- find population of some organism that's not in trouble and borrow some individuals for mating because they can bring genetic diversity
88
mechanisms to avoid inbreeding
- done by plants and animals in the wild
- mate choice, genetically controlled self-incompatibility {cant self-pollinate, forced to mate with randoms}, dispersal
- sometimes it can't be avoided in small populations
= common problem for rare and endangered species (if they're cut off they'll be more related to each other on average)
= problem for captive breeding programs
89
Inbreeding amongst the Florida Panther
- Floridas urbanization caused the population of panthers to become isolated [were once widespread in Canada and the states]
= began inbreeding
- by late 20th century, population shrunk to 20-25 adults
- genetic diversity was rapidly lost (lost alleles, non-random mating through inbreeding)
- genetic analysis saw inbreeding, and extinction was predicted
EFFECTS
- poor sperm quality
- low testosterone
- low fecundity (only having 1 pup instead of 2-3)
- kinked tails (leaves them less agile which hunting)
- higher risk of disease and contracting parasites
etc
90
Hybridization
mating btwn individuals of 2 genetically distinct populations
= extreme version is hybridizing btwn two diff species i.e. Liger
- negative effects on biodiversity (turbidity (debris in water) lead to less hybridization amongst sticklebacks in BC)
2 types: interspecific and intraspecific
91
interspecific vs intraspecific hybridization
interspecific: between species
intraspecific: within a species (Florida panthers)
- you don't want either of them
92
Hybrid Sink
- situation where immigration of locally unfit genotypes produces hybrids with low fitness that reduces local abundance
= weigh out the pros and cons
- help them but also don't hinder anything they use to adapt
*For the panthers, you want to introduce new alleles*
93
Hybrid Vigour (Heterosis)
- hybrid offspring have increased fitness than either of the parents (or parental offspring)
94
Genetic Rescue
- environmental change, invasive species, overharvesting,etc. are threats to biodiversity
- requires we act aggressively for conservation
GENETIC RESUCE= taking alleles from a healthy OUTBRED population and introduce them into an inbred population
- leads to increase in population fitness
- reduces extinction risk
- causes population level demographic
95
debate over genetic rescue
1) translocated inividuals/alleles into small populations will lead to increased population by increasing fitness [reduce inbreeding]
2) reduce population fitness via outbreeding depression [reduced fitness of offspring from matings between genetically divergent individuals]
96
opposite of inbreeding depression
outbreeding depression
- when individuals from different populations or species mate, and their offspring experience reduced fitness due to the mixing of incompatible genetic material.
97
genetic rescue is used to restore diversity and increasing fitness 4
small populations
- usually (not always) suffering from inbreeding
- idea: low levels of immigration should be enough to decrease frequency of bad alleles and provide substantial genetic variation
- you also don't want to kill off locally adaptive variation so keep immigrant numbers small
98
Problem with GR
the Ibex
-the introduced ibexes struggled with the harsh winter conditions because they were not adapted to the specific environment, leading to their high mortality.
99
Extinction vortex
- as population decreases, increased risk of extinction
= inbreeding depression can lead to extinction vortex
100
Saving Florida Panthers
- 8 Texan female pumas (bc obv females can carry children) are moved there
- other panther types include: CFP [canonical], EVG [ everglades], TX [texas]
[note: before urbanization lead to isolation, there were frequent gene exchange between Texan and Florida panthers]
- producing 26.6 kittens annually (compared to 2 viable kittens before)
- you still want a balance because you don't want to deplete the TX population and cause outbreeding
- now they are all hybrids with texan population
101
saving the panthers and age
- the age when they were close to extinction was high (but this is bad because it means there are barely any children to carry on the bloodline)
- after GR, decease in the average age from 6.6 to 4.4 years old
at this point, the hybrid (F1) adults had higher survival than the inbreds (CFB)...
F1 had higher sperm too (20.5% vs 5.4%)
- avoiding the defects (i.e. kinked tails) with GR
102
Praire Chickens
- population decreased to fewer than 50 [Illinois]
- fitness (fertility, hatch rates, genetic diversity) declines
- poor reproductive performance lead to predictions of extinction
-----------
saving the chickens:
objective
1) increase numbers
2) increase genetic diversity and fitness in population
- 271 chickens were brought from Minnesota, Kansas, and Nebraska
= helped
103
Experimental issues with GR
- overall GR proves beneficial (works 75% of the time)
- but studies can be controversial because you can't really have a control group so determining cause/effect is difficult
- increases in population growth could simply be the result of favourable environmental factors
= but genetic variation and data makes us more lenient to not believe the environmental reasoning
104
sexual selection
- favours individuals with specific traits that enhance their ability to mate with individuals of the opposite sex
= usually acts on the males who possess a range of ornaments (brightly coloured feathers, long tails, antlers, etc)
HAS 2 COMPONENTS
{INTERSEXUAL SELECTION}
- based on the interactions btwn males and females
- males do things that females associate with strength and good health
usually the cause of SEXUAL DIMORPHISM- differences in size/appearance of males and females
{INTRASEXUAL SEXUAL}
- selection based on interactions between members of the same sex (i.e males competing for a female)
sexual selection = directional selection (pushing phenotype to extreme)
- sometimes organisms will have these specific ornaments even if its energy-costly
105
Why do males impress females
SEXUAL ASSYMETRY:
- eggs are more energetically expensive to make than sperm and are limited in number
- females are more heavily associated with successful reproduction than males
- female fitness= producing eggs and rearing healthy kids
VS MALES
- sperm is cheap to produce
- males can father a large number of offspring
- male fitness is limited by the number of females it can mate with
Therefore, females need to be more discriminatory over the males they mate with, they need a healthy males since they only have so many eggs
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Diploidy
refers to having two sets of chromosomes, one from each parent, resulting in a total of two copies of each gene
- maintains genetic variability
- preserves recessive alleles at low frequencies in large populations
- in small populations, NS and genetic drift can eliminate harmful recessive alleles
HOWEVER
- recessive alleles still represent genetic diversity and even if they're harmful, with environment changes they can prove useful
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Balancing selection
- type of natural selection where more than 1 allele is actively maintained in a population
NS preserves this when
1) heterozygotes have higher relative fitness
2) when different allele are favoured in diff environment
3) when rarity of a phenotype provides a selective advantage
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Heterozygote Advantage
- balanced selection can be maintained this way (when heterozygotes have higher fitness than either homozygote)
- being heterozygous at many gene loci allow organisms to respond effectively to environmental variation
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Heterozygote Advantage and Sickle allele (HbS)
- codes for a defective form of hemoglobin in humans
- HbS differs from normal HbA by 1 a.a.
- causes rbc to form a sickle shape (sickle cell anemia)
- homozygous HbS/HbS die of sickle cell before reproducing, but HbS/HbA make up 25% of tropical and subtropical Africa
= sickle cell is common in regions where malarial parasites infect rbc in humans, when HbA/HbS contract malaria, their infected rbc assume the same sickle shape as HbS/HbS
= cells lose potassium, killing the malaria parasites and limiting spread
= heterozygotes individuals survive
N.S. preserves the HbS for that reason
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polymorphism is
controlled by several gene loco
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frequency-dependent selection
- rare phenotypes have higher fitness at times
- will increase in frequency until it becomes so common that it loses advantage = frequency-dependent selection
- because the selective advantage depends on FREQUENCY in population
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why is non random mating not an agent of microevolution
influences genotype frequencies without altering allele frequencies
