Analyze and evaluate the effects of other evolutionary mechanisms, including genetic drift, gene flow, mutation, and recombination.

Unit 117F

Let’s remember…

• An allele is an alternative form of one gene

B stands for black b stands for brown

The allele would be…

Genetic Drift

• An evolutionary mechanism in which allele frequencies change in a population

Allele frequency changes due to…

• Natural disaster like flood, fire, or earthquake• A random change of the

population (some are eliminated)• Different from natural selection

b/c its by chance or randomly

Original Pop

R = red star r = green heart

Pop after change

6R, 5r 5r

Bottleneck Effect

• The change in allele frequency where only genes of the surviving population members can be passed to future generations

Gene Pool

• the sum of all the genes in an interbreeding population

Gene Pool

• 2 blue alleles• 1 red allele• 12 green alleles

Founder Effect

• The change in allele frequency in a gene pool that changes from a large population to a small population• Ex: small number of individuals get

separated from a larger population… the change in the allele frequency is the founder effect

Founder Effect

Gene Flow

• Occurs when the genes of 1 population flow into a different population• This change causes a shift in allele

frequency

Immigration• Alleles move INTO a population

Emigration

• Alleles move OUT OF a population

Lots of gene flow…

• Slows down evolution• Lots of new alleles coming into

and out of a population• More genetic variation within a

population• Makes 2 populations more similar

Lack of gene flow…

• Less variation within a population• Makes 2 populations more

different and separates them

Mutation

• Any change in the genetic material of a cell• Can occur within individual genes

OR• Can involve changes in piece of

chromosomes

• If the mutation is beneficial to the organism, the mutation will be passed on to offspring • Slowly over time the mutation

will become more common in a population

Recombination

• A source of heritable variation• Occurs for 2 reasons:a. Independent assortmentb. Crossing over

Independent Assortment

Crossing Over

Hardy-Weinberg Principle

• States that allele frequencies in a population will remain constant unless one ore more factors cause those frequencies to change

Hardy-Weinberg Equation

P2 + 2pq + q2 = 1

Homozygous dominant

Homozygous recessive

Heterozygous

p = dominant allele frequency q = recessive allele frequency

Genetic Equilibrium

• The situation in which allele frequencies remain constant (don’t change)• If frequencies don’t change, the

population doesn't evolve

Conditions required to maintain genetic equilibrium:

1. Random mating2. Population must be large3. No immigration or emigration4. No mutations5. No natural selection