monday, april 7 th genetics of populations. population genetics vocab population: a localized group...
TRANSCRIPT
Population Genetics Vocab
Population: A localized group of individuals belonging
to the same species
Species: A group of populations whose individuals
have the potential to breed and produce fertile offspring
How do populations change over time?
GENOTYPE is inherited NOT the phenotype
Mutations: A change in an organism’s DNAOriginal source of new allelesMutation types: Lethal, Neutral,
Beneficial
How do populations change over time?
Individuals are selected, but populations evolve
Evolution = a change in frequencies of alleles in the gene pool of a population
How do populations change over time?
Relative Frequency:How often alleles are found in the pop.
Genetic Equilibrium:When the allele
frequency is unchanging
EVOLUTION stops
What is the Hardy-Weinberg Principle?
Serves as a model for a non-evolving population
5 CONDITIONS1) Mutations are not occurring2) Population is infinitely LARGE3) No migration in/out of the population4) Mating is totally random5) Natural selection is not occurring
What is the Hardy-Weinberg Principle?
Equation - under ideal conditions you could easily predict genotype frequencies from allele frequencies
For two alleles (which we will call A and a), the Hardy-Weinberg equation is based on the binomial distribution:
p2 + 2pq + q2 = 1
p = frequency of A q = frequency of a p + q = 1
What is the Hardy-Weinberg Principle?
p2 is the frequency of AA homozygotes 2pq is the frequency of Aa heterozygotes q2 is the frequency of aa homozygotes
H-W can be viewed as an extension of the Punnett square, using frequencies other than 0.5 for the gamete (allele) frequencies
What is the Chi-square test?
Is used to compare OBSERVED data with data we would EXPECTIs there a significant difference between the
expected frequencies and the observed frequencies in a population?
Do the number of individuals that fall in each category differ significantly from the number you would expect?
What are the types of natural selection?
3 types of natural selection:1. Directional
•Favors one extreme phenotype over the other
•Usually seen in environments that have changed over time•Changes in weather, climate, or food availability
What are the types of natural selection?
Example of DIRECTIONALDarwin’s finches on the Galapagos IslandsThe beak length changed over time due to
available food sources When there was a lack of insects to eat, finches
with larger and deeper beaks survived because they could crack seeds
Over time, as insects became more plentiful, directional selection favored finches with smaller and longer beaks.
What are the types of natural selection?
2. Diversifying or DisruptiveOccurs when selection favors the
extreme trait values over the intermediate trait
The population is divided into 2 distinct groups•Plays an important role in speciation
What are the types of natural selection?
Example of Diversifying or DisruptivePeppered mothsIn rural areas, the peppered moths were almost
all a very light color. These same moths were very dark in color in
industrial areas. It seems that the darker colored moths survived
predators in the industrial areas by blending in to the polluted surroundings.
What are the types of natural selection?
3. Stabilizing Occurs when selection favors the
intermediate trait (the middle or average trait) over the extreme traits
Ex: Siberian Huskies•Strong leg muscles•Heavier muscles would mean sinking in
the snow •Run slower pulling the sled
What are the types of natural selection?
Example of StabilizingHuman birth weight is not only a polygenic
trait, but it is also controlled by environmental factors
Infants with average birth weight are more likely to survive than a baby that is too small or too large. The bell curve peaks at a birth weight that has the minimum death rate.
What is Genetic Drift?
Changes in the gene pool of a small population due to chance
In each generation, some individuals (by chance) leave behind more descendents than others
Based on LUCK, not healthier or better
What is the Bottle Neck Effect?
Populations are reduced to small size for at least 1 generation & recover
Reduces genetic variation
Does not represent original population
Examples of bottle neck effect
CheetahsSo little genetic variation, skin grafts
from one to another do not trigger an immune response
Elephant sealsAround 30 members were alive in the
1890’sTens of thousands today
Example of bottle neck effect
European BisonAll alive today descended from a
population of 12More prone to diseasesIncreasing rates of male infertility
Example of bottle neck effect
Florida PanthersOne of the rarest mammals on EarthTotal of 80 in the wildCrooked tailsHeart defectsReproductive
abnormalities
What is the Founder Effect? A couple of organisms become
separated from a population
A new colony is started by a few members of the original population
All genetic variation is limited to those isolated individuals
How do “new” species develop?
Geographic isolation2 populations are separated by
geographic barriers; such as mountain ranges, rivers
How do “new” species develop?
Behavioral isolation2 populations are capable of
interbreeding but have differences in courtship rituals