Download Microevolution and Population Genetics

I. Connecting genotype and phenotype
Microevolution and Population Genetics
A. More than Molecular Evolution
1. Molecular evolution demonstrated consequences at ____________________
2. Alluded to interactions with molecular phenotytpes (e.g. proetins)
3. Considered within an individual primarily
B. Want to consider changes at population level - beyond the individual
1. ______________________________ - 1920s
a. changed approach toward considering evolution
b. focus on changes in gene frequencies in populations
c. formed the basis for field of population genetics
d. population genetics allowed for modern synthesis
- population genetics
- Darwinian natural selection - required population level changes
i.e. population pressure
e. Previously focus on mutations in individuals
- T.H. Morgan - mutationism
C. Some Definitions
1. Morphological, physiological, biochemical, of behavioral characteristic of an organism, or group that
differ in this respect from other individuals. Can refer to more than one characteristic.
____________________
2. Genetic constitution of an individual organism, at one or more loci singled out for discussion.
Often but not always differ in their phenotype or, conversely may manifest in more than one phenotype.
____________________
3. Site on a chromosome, often a gene that occupies a site.
____________________
4. Particular form of gene of locus. Criteria for determination can vary depending on circumstances (e.g.
comparing proteins, comparing DNA sequences).
____________________
D. Sources of Phenotypic variation
1. Differences in ____________________
a. differences in DNA sequence at one or moe loci
2. Differences in ____________________
a. many traits are affected by immediate or recent environmental conditions
b. environmental conditions may change throughout life
c. may be effected by environmental conditions during development
3. ____________________
a. influence of non-genetic effects of mother
b. e.g. egg yolk composition, maternal care, mothers physiological condition
c. some consider this under #2
d. some, but few, non-genetic paternal effects have been described
4. ____________________
(those those present at birth) may be non-genetic
a. phenotypic variation arises from both ____________________
E. Significance of Mendelianism
1. ____________________
a. theory of inheritance in 1800s
b. factors responsible for trait blended together to intermediate stage
c. counter-intuitive to Darwin s evolutionary ideas
- blending causes ____________________
2. Inheritance of aquired characteristics
a. still major player in 1800s and 1900s
b. put to rest by ____________________
c. noted distinction of ____________________
- changes in somatic cells could not confer informational changes to germ cells
3. Mendel s Experi ments
a. showed that inheritance was ____________________
- did not blend but maintained characteristic information
b. Loci were ____________________
- however, interactions among loci could occur to effect phentotype
- did not deal with linkage yet
NOTES FROM BOARD
18,385 total moths examined
A1A1 = 17,062
A1A2 = 1,295
A2A2 = 28
18,385 total moths examined
A1A1 = 17,062
A1A2 = 1,295
A2A2 = 28
British Population
Tested 283 people
+/+ = 223
+/ ∆32 = 57
∆32/ ∆32 = 3
G. Quick review of combining probabilities
1. Combing Two Independent events
a. role of a die
b. probability of getting a 6 is 1/6
c. combined probability that two indpendent events will occur together is the
____________________
d. Roll two dice
- probability of getting two ones at the same time
- ____________________
- p(two ones) = 1/6 X 1/6 = 1/36
2. Combining Two Mutually Exclusive events
a. probability that either of two mutually exclusive events will occur is the
____________________
b. roll a die
- ____________________
- p(one or two) = 1/6 + 1/6 = 1/3
G. The Hardy-Weinberg Principle
1. General Case
a. imaginary population with alleles A1 and A2
b.
c.
d. From Allele frequency calculations we know that
e. four possible combinations of alleles
f. Punnett Square also exemplifies gametic combinations
g. All possible zygotes (genotypes) produced in population
g. If zygotes grow up to reproduce freely what should Allele frequencies be?
- Check allele frequency of A1 after one generation of breeding
- A1 gametes carried by A1A1 individuals (p2 of population) - ____________________
- A1 gametes carried by A1A2 individuals (2pq of population) - ____________________
- Fraction of A1 gametes =
Fraction of A1 gametes in next generation = ___
Same as ____________________
h. What s the *&#$in g Point?
- Allele frequencies in a population ____________________
i. If they do something is up
- If allele frequencies in a population are p and q,
____________________
i.If the measured genotype frequencies are not in these proportions
something is up
- A population in which these two conclusions are realized is said to be in
____________________
i. Assumptions of Hardy-Weinberg Principle
1. ____________________
- each individual finds its mate at random from population sample
2. ____________________
- Actually it assumes infinite population size but tolerates l arge enough to act as inf inite
- Your text - No Chance Events
- Smaller population size may allow chance alterations in genotype production from generation to
generation
- May get ____________________
3. ____________________
- Alleles are not added from outside the population
- Gene Flow may alter allele frequencies
4. ____________________
- do not get change from one allelic State to another
i. No new alleles
ii. No conversion to existing alleles
5. ____________________
- All individuals have equal probabilities of survival and reproduction
- no consistent differences survival and reproduction among genotypes
* These assumptions define the forces that cause evolution
* If a Population is out of Hardy-Weinberg Equalibrium,
____________________
- Step 1- Test for Hardy-Weinberg equilibrium
- Step 2 - determine which assumption(s) are violated
j. Test for Hardy-Weinberg Equilibrium - NOTES FROM BOARD
18,385 total moths examined
A1A1 = 17,062
A1A2 = 1,295
A2A2 = 28
II. Genetic Drift
A. Background
1. Genetic Drift often considered the null hypothesis in evolution
a. unless can prove change occurred via selection, must be drift
2. Many populations violate assumption of large population size
a. so what?
b. As population size
, likelihood of chance shifts in allele frequencies
- due strictly to sampling error in production of zygotes
c. When allele frequencies fluctuate by chance alone = ____________________
B. Variance as Function of Population Size
1. Random Fluctuation
a. assume frequencies of alleles A1 and A2 are ____________________
b. might assume many independent populations
- often refer to assemblage of populations as ____________________
- within metapopulation one finds individual populations = ____________________
c. ____________________
d. each population has ______breeding individuals (N can vary among pops)
- represents 2N gene copies
e. After breeding, offspring mortality leads to population of N individuals
- end up with new allele frequencies (e.g. ____________________
f. for pop of infinite size we would expect ____________________
- for finite populations p ca n vary
-Variance in allele frequency after 1 generation
____________________
for diploid adults
N = # of individuals in population
- note that variance of p from one generation to next depends strongly on N
i. variations in sampling from initial frequency likely to greater when N is smaller
g. Random walk
- If initial frequency p = 0.5
i. Small population
ii. p li kely to ____________________
iii. p m ay even ____________________
- Over time, p will drift to either ____________________
i. Once at 0 or 1 it can not change without introduction of new allele
- mutation or gene flow
- Process known as ____________________
h. probability at time t, that allele will become fixed equals its frequency (p t) at that time
- like drunk on railway
- closer to edge - more likely to reach edge and fall (fixed or eliminated)
- pt = 0.70 then 0.70 chance of becoming fixed
i. Evolution by genetic drift proceeds ____________________
-variance greater per generation
- average time to fixation
i. Newly arisen neutral allele
ii. ____________________
iii. Most likely to be lost
V = p(1-p)/2N
For N=9, p = 0.5
V=
For N=100, p=0.5
V=
For N=10,000, p=0.5, V=
j. Frequency of heterozygotes declines over time
- Heterozygote frequency is highest when ____________________
- Drift eventually to fixation causes decline in heterozygosity
- Genetic Drift ____________________
- Rate of reduction associated with rate of fixation
i. Rate of heterozygote decline ____________________
k. Experimental Results of drift
- P. Burti (1956)
- Drosophila melanogaster
- measured 107 populations of flies
- N = 16 (8 female, 8 male)
- ____________________
i. ____________________
ii. p = 0.5 in all pops
- monitored for ____________________
i. 8 males and 8 females selected at random
- At generation 19
i.30 pops ____________________
ii. 28 pops ____________________
iii. Allele freqs among unfixed pops evenly distributed
- results expected from theory of genetic drift
i. Except ____________________
ii. Why?
C. ____________________
1. Until now we assumed idealized populations
a. N = population size
b. assumed all members in N ____________________
c. Real populations - not all members of population ____________________
2. Measuring actual number of adults indicates ____________________
a. Does not necessarily represent genetic contributors
3. Rates of drift of allele frequencies and heterozygote loss ____________________
a. ____________________
b. Population is effectively smaller than in ideal population
4. The number of individuals in a population that actually contribute to gene pool of next generation =
____________________
D. ____________________
1. Restriction size through which a population may pass
____________________
a. Drastic and rapid drop in effective population size
2. New Populations
a. ____________________
- Often via unlikely ____________________
b. Get only ____________________
from main population
c. population sizes are small so ____________________
d. In very short time get drastic shift allele frequencies
- perhaps in large main population, shifts were minor
- rare alleles in main population can become fixed in new population
e. Typically drastic ____________________
e. Shifts in allele frequency away from that of original population due to formation of new small
population and associated genetic drift
____________________
3. Example of Bottleneck Effect
a. Northern Elephant Seals
b. Genetic studies show very ____________________
c. Population Census over 30,000
d. Previous population bottleneck due to hunting
e. Population reduced to ____________________
f. Effective population size ____________________
a. typically ____________________