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Transcript
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.