When and how does a population change

genetically?An accelerated biology introduction to Hardy-

Weinberg

The frequency of alleles (dominant, recessive) in a population REMAIN in equilibrium unless an external pressure acts upon them or they are a very small population and change by chance. PRESSURE:

NATURAL SELECTION: forced selection SEXUAL SELECTION: mate choice GENE FLOW:

Immigration: Alleles enter a population Emigration: Alleles exit a population

Equilibrium

Genotypic Frequencies: p2 + 2pq + q2 = 1

AA + Aa + aa = 1 Allele Frequencies:

p + q = 1 A + a =1

Genotypic frequencies can change in a population that is not evolving but allele frequencies must remain the same. How can this be true?

Two Equations must be used to determine the genotypic and allele frequencies in a

population.

The historical allele frequencies for a population of rainforest frogs that exhibit the recessive trait albinism is: .8 dominant allele and .2 recessive allele

You are sent out to study if the allele frequency is changing. You count 50 white frogs and 650 green frogs.

Is this population in equibrium? Mathematically show why or why not!

Sample question

What might you conclude about the frogs you studied?

In a population of frogs in equilibrium, the amount of white frogs can change from one generation to the next. How can the population of frogs be in equilibrium, yet you see a change in the number of white frogs?

Followup: