Transcript Section 1 Genetic Equilibrium Chapter 16 The Gene Pool

Chapter 16
Section 1 Genetic Equilibrium
Objectives
• Identify traits that vary in populations and that may be studied.
• Explain the importance of the bell curve to population genetics.
• Compare three causes of genetic variation in a population.
• Calculate allele frequency and phenotype frequency.
• Explain Hardy-Weinberg genetic equilibrium.
Chapter 16
Section 1 Genetic Equilibrium
Variation of Traits Within a Population
• Population biologists study many different traits in
populations, such as size and color.
• Population genetics – study of evolution from a
genetic point of view
• For example: Studying dogwood trees in Middletown,
Connecticut would be a way to describe a population
Chapter 16
Section 1 Genetic Equilibrium
Variation of Traits Within a Population,
continued
• Causes of Variation
– Traits vary and can be mapped along a bell
curve, which shows that most individuals have
average traits, whereas a few individuals have
extreme traits.
– Variations in genotype arise by mutation,
recombination, and the random pairing of
gametes.
Chapter 16
Section 1 Genetic Equilibrium
The Gene Pool
• The total genetic information available in a population
is called the gene pool.
Chapter 16
Section 1 Genetic Equilibrium
The Gene Pool, continued
• Allele frequency is determined by dividing the total
number of a certain allele by the total number of
alleles of all types in the population.
Chapter 16
Section 1 Genetic Equilibrium
The Gene Pool, continued
• Predicting Phenotype
– Phenotype frequency is equal to the number of
individuals with a particular phenotype divided by
the total number of individuals in the population.
• Allele frequencies in the gene pool do not change
unless acted upon by certain forces.
Chapter 16
Section 1 Genetic Equilibrium
Phenotype Frequency
Chapter 16
Section 1 Genetic Equilibrium
The Hardy-Weinberg Genetic Equilibrium
• Hardy-Weinberg genetic equilibrium is a
theoretical model of a population in which no
evolution occurs and the gene pool of the population
is stable.
• Certain conditions are needed: no mutations occur, the
population is infinitely large, individuals neither leave nor
enter the population
Chapter 16
Section 2 Disruption of Genetic
Equilibrium
Objectives
• Explain how migration can affect the genetics of equilibrium
• Explain how genetic drift can affect populations of different
sizes.
Chapter 16
Section 2 Disruption of Genetic
Equilibrium
Gene Flow
• Immigration – the movement of individuals into a
population
• Emigration – movement of individuals out of a
population
• If individuals are moving in or out a population the
genetics of that population will change…if individuals
move, genes move with them.
Chapter 16
Section 2 Disruption of Genetic
Equilibrium
Genetic Drift
• Genetic Drift is the phenomenon by which allele
frequencies in a population change as a result of
random events, or chance.
• The larger the population the more stable the
genetics will stay, the smaller the more things can
change.
• Figure 16-5
Chapter 16
Section 3 Formation of Species
Objectives
• Relate the biological species concept to the modern definition of
species.
• Explain how the isolation of populations can lead to speciation.
• Compare two kinds of isolation and the pattern of speciation
associated with each.
• Contrast the model of punctuated equilibrium with the model of
gradual change.
Chapter 16
Section 3 Formation of Species
The Concept of Species
• Speciation - formation of new species as a result of
evolution
• Morphology – study of the structure and form of an
organism (this is the major way to classify organisms)
• Major limitations of the morphological concept:
• There may be a great deal of phenotypic variability in
a species
• Organisms that actually can interbreed may have very
different physical characteristics
• It does not consider whether individuals of a species
can mate and produce viable offspring
Chapter 16
Section 3 Formation of Species
The Concept of Species
• According to the biological species concept, a
species is a population of organisms that can
successfully interbreed but cannot breed with other
groups.
Chapter 16
Section 3 Formation of Species
Isolation and Speciation
• Geographic Isolation
– Geographic isolation results from the separation
of population subgroups by geographic barriers
– Ex. Canyon could form to divide a population
– Speciation can occur as a result of geographic
isolation because populations that live in different
environments may be exposed to different
selection pressures
Chapter 16
Section 3 Formation of Species
Isolation and Speciation, continued
• Allopatric Speciation
– Geographic isolation may lead to allopatric
speciation.
– When this occurs new species arise as a result
of geographic isolation
Chapter 16
Section 3 Formation of Species
Isolation and Speciation, continued
• Reproductive Isolation
– Reproductive isolation results from the
separation of population subgroups by barriers to
successful breeding.
– Two types of reproductive isolation
– Prezytoic – occurs before fertilization
– Postzygotic – occurs after fertilization
– Reproductive isolation differs from geographic
isolation in that members of the same species are
not physically separated in repro. Isolation,
whereas they are separated in geo. separation
Chapter 16
Section 3 Formation of Species
Isolation and Speciation, continued
• Sympatric Speciation
– Sympatric speciation occurs when two
subpopulations become reproductively isolated
within the same geographic area
– Ex. A population of insects might live on a single
type of plant. If some of the individuals from this
population began to live on another type of plant,
they would no longer interbreed with the original
population
Chapter 16
Section 3 Formation of Species
Rates of Speciation
• In the gradual model of speciation (gradualism),
species undergo small changes at a constant rate.
• Under punctuated equilibrium, new species arise
abruptly, differ greatly from their ancestors, and then
change little over long periods.