Download 9.1 - How Do Populations Evolve SG

9.1 HOW DO POPULATIONS EVOLVE?
The percentage of any specific allele in a gene pool is called the allele frequency. A population in which
an allele frequency remains the same over generations is in a stable condition known as genetic
equilibrium. A population that is in genetic equilibrium is not evolving in any way relate to that gene.
Any factor that affects the genes in the gene pool can change allele frequencies, disrupting a
population’s genetic equilibrium, and resulting in the process of microevolution.
-
Populations consist of all members of a species that live in an area at a certain time. Each
member has the genes that characterize the traits of the population, and these genes exist as
pairs of alleles.
-
All of the genes of the population’s individuals make up the population’s gene pool.
-
Evolution occurs as a population’s genes and their frequencies change over time.
-
Natural selection favours some phenotypes over others, and causes populations and species to
evolve over time. Individuals don not evolve.
There are four agents, or causes, of evolutionary change; mutations, gene flow, non-random mating,
and genetic drift.
Mutation: a change that occurs in the DNA of an individual.
Gene flow: the net movement of alleles from one population to another due to the migration of
individuals.
Non-random mating: mating among individuals on the basis of mate selection for a particular
phenotype or due to breeding.
Genetic drift: the change in frequencies of alleles due to chance events in a breeding population.
Founder effect: a change in a gene pool that occurs when a few individuals start a new isolated
population.
Bottleneck effect: changes in gene distribution that results from a rapid decrease in population size.
9.1 HOW DO POPULATIONS EVOLVE?
Agents of Evolutionary Change
Mutations:
-
-
-
-
Gene Flow
-
-
-
Non-Random Mating
-
-
-
-
Illustration
9.1 HOW DO POPULATIONS EVOLVE?
Agents of Evolutionary Change
Genetic Drift – Founder Effect
-
-
-
Genetic Drift – Bottleneck Effect
-
-
-
Illustration
9.1 HOW DO POPULATIONS EVOLVE?
Learning Check:
1. Define or describe each term.
a) Gene Pool:
b) Allele Frequency:
c) Genetic Equilibrium:
d) Microevolution:
2. a) What role do mutations play in evolution?
b) Describe what can happen to a mutation and the effects the mutation may have on the population.
3. Compare and contrast the founder effect and the bottle neck effect.
4. Many species of plants, such as, the common pea plant, can self-pollinate.
a) Which agent of evolution is likely to occur in plants that self-pollinate?
b) Describe the impact self-pollination can have on a population.