analyze and evaluate the effects of other evolutionary mechanisms, including genetic drift, gene...
TRANSCRIPT
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
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
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