Download POPULATION GENETICS – 3/27/07

POPULATION GENETICS – 3/27/07
1. Natural selection is the interaction between the environment and (individuals), which
vary in heritable traits.
2. Evolution occurs at the level of the (population).
3. In microevolution, a population—a localized group of organisms of the same
species—is studied by looking at their gene pool, or total composition of genes at that
time.
4. Below is an example of the proportion of a population that has a particular allele,
a.k.a. the allelic frequencies.
The phenotype of a population of humans is curly hair (CC), wavy hair (Cc) and
straight hair (cc). The phenotypes seen from these genotypes create an example of
incomplete dominance (think back a couple lectures!).
Phenotypes
Genotypes
Number of
Individuals
Frequency
Curly Hair
Wavy Hair
Straight Hair
CC
Cc
cc
60
30
10
0.60
0.30
0.10
What are the allele frequencies? What do the frequencies add up to?
Frequency of C: (60 + 60 + 30)/200 = 0.75
Frequency of c: (30 + 10 + 10)/200 = 0.25
Frequency of dominant allele + recessive allele = 0.75 + 0.25 = 1 (or 100%)
How might you find out if the above population is changing?
Examine their allelic frequencies at another point in time to see if it is evolving/changing.
1. What does the Hardy-Weinberg Theorem state? States: Allele frequencies in a
population will remain constant between generations if only Medelian
segregation and recombination are at work Are the specific conditions realistic?
No! What is the equation that goes with the theorem? p2 + 2pq + q2 = 1
2. What five conditions must the population studied meet to follow the Theorem?
Very large population size (N)
No migration
No mutations
No natural selection
Random mating
If they don’t meet those five conditions, what will happen to the population? They
will evolve!
3. What are the four causes of microevolution? Genetic drift Natural selection Migration
(gene flow) Mutation What are the main ones? Genetic drift and natural selection.
4. What is genetic drift? Changes in allele frequency due to chance(Is it random or
predictable? Random!) What does it do to the allele frequencies? Makes them vary
unpredictably!
5. Describe the Bottleneck Effect and how it affects genetic diversity.
If most of the population is killed, some genetic variability will be lost
6. Describe the Founder Effect and how it affects genetic diversity.
Few members of a population establish a new (isolated) population
New gene pool does not reflect the diversity of the original population
New gene pool ≠ old gene pool
7. What is Natural selection?
Natural selection is the interaction between individuals that vary in heritable
traits and the environment.
Natural selection acts on the ____individual________.
Evolution occurs at the ____population______.
How does it affect allele frequencies in a population? It causes some to become more
frequent if compatible with the environment and others to be less frequent if
incompatible. Natural selection is the only process that is adaptive to the environment.
8. What three types of selection are there for natural selection? Briefly describe each.
Directional selection
Disruptive selection
Stabilizing selection
9. What three things prevent natural selection from reducing genetic variation? How do
they each maintain diversity?
Diploidy - cna hide genetic diversity, unfavored genes can persist and eventually be
useful
Heterozygote advantage - more options
Neutral variation
Changing environment
10. Sexual reproduction (increases/decreases) (phenotypic/genetic) diversity within a
population. How? Random fertilization/mating patterns, crossing over events in meiosis,
biparental inheritance, etc.
11. Natural selection works on that diversity, (increasing/decreasing)
(phenotypic/genetic) diversity within a population. How? Some genetic traits will
decrease because it is not favorable for a population to have it in a certain environment.