Name ____________________________________________ Period _________ Date ______________
Hardy Weinberg Principle (equilibrium)
• Allele frequencies will remain constant unless one or more factors cause
the frequencies to change.
• If there is no change, there is no evolving.
• When will evolution not occur?
• What conditions must exist under which evolution will not occur?
• How can we tell if evolution won’t take place?
• Can Individuals Evolve?
• Genes determine most of an individual’s features.
• Individuals cannot evolve a new phenotype in response to their
environment.
• Populations, not individuals, evolve.
Evolution of a Population
• ______________________ selection acts on the range of phenotypes in a
population
• Evolution occurs as a population’s ____________ and their frequencies
____________ over time
• How can a population’s genes change over time?
• All of the alleles of a population’s genes together make up a __________
___________
• ___________ frequency - % of any specific allele in the gene pool.
• Genetic _________________ – a population in which the frequency of alleles
remains the same over generations.
• Conditions that cause changes in
Genetic Equilibrium
• A population in genetic equilibrium is not evolving.
• _____________ are one cause of genetic change.
• ___________ mutations disappear quickly, but mutations that cause a
useful variation become part of the gene pool
• Conditions that cause changes in
Genetic Equilibrium
• Genetic drift – the change of allele ______________ by chance events
• Gene flow – ____________ of genes into or out of a population by migrating
individuals
• Genetic drift, gene flow, and mutations can greatly affect __________
populations
• _____________ selection is usually the most significant cause of changes in
any gene pool
• Natural Selection Acts on Variation
• Some variations ____________ or decrease an organism’s chance of
survival in an environment
• Variations are controlled by ___________
• Allelic frequencies in a gene pool will change due to natural selection of
____________
• If conditions are not met the genetic equilibrium is disrupted –
*population evolves and changes*
• If conditions are met the genetic equilibrium stays the same–
*population does not evolve*
• Genotype Proportions
• Genotype proportions remain constant – calculated from allele
frequencies
P+Q = 1 or 100 percent
(_____________ frequencies)
P2 + 2PQ + Q2 = 1 or 100 percent
(_______________ frequencies)
• Key Information
• P = frequency of the ____________ allele in the population
• Q = frequency of the ___________ allele in the population
• P2 = percentage of _________________ dominant individuals
• Q2 = percentage of _________________ recessive individuals
• 2PQ = percentage of _________________ individuals
• Question
• If 98 out of 200 individuals in a population express the recessive
phenotype, what percent of the population are
homozygous dominant?
Answer:
Recessive phenotype = homozygous genotype
P+Q=1
Q2 = 98/200 = 0.49
or
Q = 0.7
P + .7 = 1
P + 1 - 0.7 = 0.3
P2 = 0.32 = 0.09
or
P = 0.3