Unit 11 7F
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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
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