Modern Synthesis Natural Selection’s effects on a Population’s Gene Pool (Darwin meets Mendel) Quiz on Friday Classification and Evolution

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Measuring evolution Natural selection act on individuals – by impacting their chances of survival – by impacting their reproductive success only apparent when looking at how a population changes over time

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Darwin’s Ideas Revisited Darwin’s ideas had to be integrated with our new found information on Genetics.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings microevolution Evolution on the scale of populations Change in the allele frequencies in a population

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Variation Quantitative Characters – Vary along a continuum anything that goes through a gradual transition from one condition, to a different condition, without any abrupt changes Discrete Characters – Polymorphism – two or more distinct morphs are represented

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Quantitative Characteristic polygenic trait - trait controlled by two or more genes

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Polymorphism single-gene trait - trait controlled by a single gene

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings population genetics genetic basis for variation and natural selection

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Genes and Variation There are two main sources of genetic variation: – Mutations – What are the two main types of mutations? – Gene shuffling – When and how does gene shuffling occur? Big question: Do mutations and gene shuffling cause evolution? In other words do mutations and gene shuffling change the relative frequencies of alleles in a gene pool?

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

modern synthesis comprehensive theory of evolution paleontology, taxonomy, biogeography, and population genetics

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings population localized group of individuals that belong to the same species Species = a group of populations whose individuals have the potential to interbreed and produce fertile offspring in nature

Modern Synthesis Natural Selection’s effects on a Population’s Gene Pool (Darwin meets Mendel) Quiz on Friday Classification and Evolution

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Genes and Variation Gene Pools - combined genetic information of all the members of a particular population Relative Frequency - number of times an allele occurs in a gene pool compared with the number of times other alleles occur

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Natural Selection on Polygenic Traits Natural selection can affect the distributions of phenotypes in any of three ways: directional selection – form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve stabilizing selection - form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end disruptive selection - form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Directional Selection

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Stabilizing Selection Stabilizing selection takes place when individuals near the center of a curve have higher fitness than individuals at either end. This example shows that human babies born at an average weight are more likely to survive than babies born either much smaller or much larger than average.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Disruptive Selection What will Disruptive Selection result in?

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings When evolution DOES OCCUR The process of SPECIATION - formation of new species Speciation has occurred when – population have become reproductively isolated from one another reproductive isolation - separation of species or populations so that they cannot interbreed and produce fertile offspring – Reproductive isolation can develop in a variety of ways, including behavioral isolation, geographic isolation, and temporal isolation.

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-4a Habitat IsolationTemporal Isolation Prezygotic barriers Behavioral Isolation Mating attempt Mechanical Isolation (f) (e) (c) (a) (b) (d) Individuals of different species

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 24-4i Prezygotic barriers Gametic Isolation Fertilization Reduced Hybrid Viability Postzygotic barriers Reduced Hybrid FertilityHybrid Breakdown Viable, fertile offspring (g) (h) (i) (j) (l) (k)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Behavioral Isolation form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding Examples – Mating calls – Mating dances

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Geographic Isolation form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig Geographic distance (km) Degree of reproductive isolation

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Temporal Isolation form of reproductive isolation in which two populations reproduce at different times

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Speciation of Darwin’s Finches Speciation in the Galápagos finches occurred by the: – founding of a new population – geographic isolation – changes in the new population’s gene pool – reproductive isolation

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Patterns in the Fossil Record Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change – The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig (a) Punctuated pattern (b) Gradual pattern Time

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig (a) Similarity between different species (b) Diversity within a species