Chapter 23 Flashcards
Memorize
Where do all new variations come from?
Mutations
Can a mutation affect the genetic frequency of a whole population?
Not generally, no
Gene flow
movement of genes from one population to another
Immigration
members of a population move to a new location.
Emigration
members of an established population leave
What do both immigration and emigration cause?
Rapid and large scale changes to genetic frequencies
Assortative Mating
a tendency of individuals to mate with phenotypically similar individuals
What is the effect of Assortative mating?
frequency of homozygous individuals rise; less diversity in resulting population
Dissassortive Mating
also called “outcrossing”, is a deliberate attempt to mate with phenotypically dissimilar individuals
What is the effect of disassortative mating?
makes the frequency of heterozygote rise, and increases diversity
Genetic Drift
All random events that can affect gene frequency in a SMALL POPULATION
Bottleneck effect
makes a large population small by some random event wherein fitness did not help survival (randomly selected genes remaining)
Founders Effect
Small group of pioneers (random selection), grows to large population that has the same genetic frequency as the founders
Selection
the name given to the effect that environmental forces (resource availability, etc) have on WHICH members of a population survive
Is selection random?
No, selection is SYSTEMIC (those who survive have the trait that will help them survive, and that trait is favored)
Disruptive selection
Favors extremes (AA + aa)
Directional Selection
Favors one extreme over another (Aa+ AA)
Stabilizing selection
Favors heterozygote
How does sickle cell anemia represent stabilizing selection?
One homozygote doesn’t show it, one homozygote kills the host, the hétérozygote that carries sickle cell benefits
Why do variations persist?
The environment keeps changing; different traits are favored for different reasons
What is the Hardy Weinberg assumption?
gene frequencies in a population will remain the same over time
What are the conditions necessary for hardy-weinberg?
Populations must be large, random mating is occurring, no selection, no mutations, and no migration.
What is the hardy-weinberg equation?
p^2 + 2pq + q^2 = 1
If the recessive gene in it’s homozygous condition became lethal, what would happen to the frequency of p & q in four generations?
p increases, q decreases (but not to 0, because it can be carried and not expressed)
If the dominant phenotype suddenly became fatal at birth, what would happen to the frequency of p and q in four generations?
decrease to p=0, increase to q = 1, since the gene can’t be carried without being expressed
