Monday, April 7th

Genetics of Populations

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

Which is which?

Which is which?

Population Genetics Vocab

Gene pool: All of the genes in a population at any one time

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

Evolutionary force? We are!

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.

Directional

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.

Diversifying or Disruptive

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.

Stabilizing

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

Genetic drift reduces genetic variability & it doesn’t work to produce adaptations

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

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

What is the Founder Effect?

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

How do “new” species develop?

Temporal isolation2 or more species reproduce at

different times

Dracula simia (monkey orchid), Orchis italica (naked man orchid), Habenaria radiata (white egret orchid) and Caleana major (flying duck orchid)