Evolution
as
Genetic Change
Objectives
• Define evolution, natural selection, and
gene pool.
• Analyze and evaluate the effects of
other evolutionary mechanisms,
including genetic drift, gene flow,
mutation, and recombination (TEKS 7F)
Evolutionary Mechanisms
Remember:
Evolution is a change in an organism over time. More
specifically, it’s the gradual change in the distribution
of alleles in a population.
Natural Selection is an important evolutionary
mechanism that drives the evolution of populations. It
is the process where individuals who are better suited
to their environment survive and reproduce the most
successfully.
Gene Pool is the combined genetic information of all
the members of a particular population.
Objectives
• Define evolution, natural selection, and
gene pool.
• Analyze and evaluate the effects of
other evolutionary mechanisms,
including genetic drift, gene flow,
mutation, and recombination (TEKS 7F)
Evolutionary Mechanisms
Natural selection is NOT the only evolutionary mechanism.
Evolutionary Mechanisms
Natural
Selection
Other
Mechanisms
Genetic
Drift
Gene
Flow
Nonrandom
Mating
Recombination
Mutation
Act on Genetic Variation in a population
Genetic Drift
Other
Mechanisms
Genetic
Drift
Gene
Flow
Nonrandom
Mating
Recombination
Mutation
• Evolutionary changes in a populations gene pool can be caused by random
events. Genetic drift is the random change in allele frequencies that
occurs in small populations.
• Example: A small group of insects migrate to a new island. This
creates a founder effect where there’s a change in allele
frequencies as a result of the migration of a small subgroup of a
population.
• Unlike natural selection, with genetic drift, the changes in a populations
gene pool are purely due to chance. They are not due to traits that
increase or decrease reproductive success and so, it does not produce
adaptations.
Other
Mechanisms
Genetic
Drift
Gene
Flow
Gene Flow
Nonrandom
Mating
Recombination
Mutation
• Different populations of the same species may have slight differences
in allele distribution.
• A population’s genetic variation can increase when alleles are added to
the population by migration. The movement of alleles due to migration is
called gene flow.
• The rate of gene flow between populations affects the probability of
speciation, or the development of new species.
• Example: When gene flow occurs at a high rate, reproductive
isolation is less likely to occur. Therefore, the gene pools are likely
to remain similar, which would reduce the probability of speciation.
Mutation
Other
Mechanisms
Genetic
Drift
Gene
Flow
Nonrandom
Mating
Recombination
Mutation
• Genetic variation occurs as a result of random mutations, or
changes in DNA sequences. If a mutation occurs in a sex cell
(sperm or egg), the mutation can be passed on to the
offspring.
• Harmful, beneficial, or neutral mutations can lead to
evolutionary changes in a population.
• Natural selection acts on both harmful and beneficial
mutations, decreasing or increasing their distribution within
the population.
Recombination
Other
Mechanisms
Genetic
Drift
Gene
Flow
Nonrandom
Mating
Recombination
Mutation
• Recombination occurs as a result of crossing-over
during meiosis.
• When gametes from two parents join, the offspring
inherit a unique combination of alleles, thereby
increasing genetic variation in a population.
Nonrandom Mating
Other
Mechanisms
Genetic
Drift
Gene
Flow
Nonrandom
Mating
Recombination
Mutation
• Nonrandom mating - occurs when some individuals have greater chances of
reproducing or can reproduce more often than other individuals in the
population.
• This type of mating can cause a population to evolve over time as only the
traits from the mating individuals are passed on.
• Example: A male deer (buck) competing with another male to mate.
Usually the dominant male is able to mate with more than one female,
passing on his alleles/traits.
Hardy-Weinberg
Principle
• When NONE of these factors are acting on a population, the frequencies of
dominant and recessive alleles remain the same across generations in a
population. This is called genetic equilibrium.
• If allele frequencies do not change, the population will NOT evolve.
• These frequencies can be calculated using the Hardy-Weinberg principle:
p= dominant allele
q= recessive allele
Frequencies of these alleles in a population is:
P2 + 2pq + q2 = 1