View
226
Download
0
Category
Tags:
Preview:
Citation preview
Chapter 16
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.
Section 1 Genetic Equilibrium
Chapter 16
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
Section 1 Genetic Equilibrium
Chapter 16
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.
Section 1 Genetic Equilibrium
Chapter 16
The Gene Pool
• The total genetic information available in a population is called the gene pool.
Section 1 Genetic Equilibrium
Chapter 16
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.
Section 1 Genetic Equilibrium
Chapter 16
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.
Section 1 Genetic Equilibrium
Chapter 16
Phenotype Frequency
Section 1 Genetic Equilibrium
Chapter 16
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
Section 1 Genetic Equilibrium
Chapter 16
Objectives
• Explain how migration can affect the genetics of equilibrium
• Explain how genetic drift can affect populations of different sizes.
Section 2 Disruption of Genetic Equilibrium
Chapter 16
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.
Section 2 Disruption of Genetic Equilibrium
Chapter 16
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
Section 2 Disruption of Genetic Equilibrium
Chapter 16
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.
Section 3 Formation of Species
Chapter 16
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
Section 3 Formation of Species
Chapter 16
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.
Section 3 Formation of Species
Chapter 16
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
Section 3 Formation of Species
Chapter 16
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
Section 3 Formation of Species
Chapter 16
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
Section 3 Formation of Species
Chapter 16
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
Section 3 Formation of Species
Chapter 16
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.
Section 3 Formation of Species
Recommended