Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Evolution and Natural Selection Chapter 11 Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Outline Gene Variation Pace of Evolution  Fossil Record  Molecular Record  Anatomical Record Hardy-Weinberg Forms of Selection Industrial Melanism Species Formation

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Gene Variation Macroevolution - Evolutionary change on a grand scale, encompassing novel designs, evolutionary trends and episodic mass extinction. Microevolution - Differential survival and reproduction due to natural selection. Gradually alters population to include more individuals with advantageous characteristics.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Gene Variation Darwin’s explanation of evolution:  Adaptation by natural selection is responsible for evolutionary changes within a species(microevolution), and accumulation of these changes leads to development of new species (macroevolution).

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Pace of Evolution Punctuated Equilibria  Proposed by Stephen Jay Gould and Niles Eldridge. - Evolution normally proceeds in spurts, with long periods of little movement in between.  Contrasted to the theory of gradual evolutionary change (gradualism).

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Fossil Record Fossils are preserved traces of once-living organisms created when organisms become buried in sediment and calcium in hard surfaces mineralizes.  Often provide evidence of successive evolution. Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Molecular Record Evolutionary theory allows evolutionary change involves substitution of new versions of old genes.  New alleles arise by mutation and come to predominate through favorable selection. Molecular Clocks  The longer the time since divergence, the greater the number of differences in nucleotide sequence of cytochrome C. - Changes accumulate at constant rate.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Molecular Clock of Cytochrome C Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Molecular Record Phylogenetic Trees  Evolutionary history of a gene can be mapped as a phylogenetic tree.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Anatomical Record Homologous Structures - Structure and function have diverged between body parts of different animals, but are derived from same part present in a common ancestor.  Forelimbs of Vertebrates Analogous Structures - Features resemble each other as a result of parallel evolution in separate lineages.  Flippers of penguins and dolphins Vestigal Organs - Organs no longer of use.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Hardy-Weinberg Rule From 1920’s onward, scientists began formulating theory of how alternative gene forms (alleles) behave in a population, and how changes in gene frequencies lead to evolutionary change.  1908 Hardy and Weinberg pointed out in the absence of forces, in a large population with random mating, allelic frequencies remain constant. - Hardy Weinberg equilibrium

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Hardy-Weinberg Equilibrium (p+q) 2 = p 2 + 2pq + q 2 p = Individuals homozygous for allele B. 2pq = Individuals heterozygous for B and b. q = Individuals homozygous for allele b.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Hardy-Weinberg Assumptions:  Large population size  Random mating  No mutation  No immigration  Absence of natural selection

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Change in Allelic Frequencies Mutation  Error in replication of a nucleotide sequence in DNA (Very slow rate). Migration  Movement of individuals from one population to another (Dependent on strength of selective forces).

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Change in Allelic Frequencies Genetic Drift  Change in allelic frequencies due to random events. - Founder Effect - Population started by few individuals and thus a restricted gene pool (Rare genes may become common). - Bottleneck Effect - Gene pool becomes very small, usually due to small population size.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Change in Allelic Frequencies Nonrandom Mating  Individuals with certain genotypes mate with more or less commonly than expected on a random basis. - Inbreeding - Mating with relatives.  Increases homozygosity

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Change in Allelic Frequencies Selection  Some individuals leave behind more progeny than others. - Artificial - Breeder selects desired characteristics. - Natural - Environment determines adapted characteristics.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Forms of Selection Disruptive  Selection acts to eliminate intermediate phenotypes. Stabilizing  Selection acts to eliminate both extremes from an array of phenotypes. Directional  Selection acts to eliminate one extreme from an array of phenotypes.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Three Forms of Selection Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Sickle-Cell Anemnia Hereditary disease affecting hemoglobin molecules.  Sickle-Cell homozygosity frequently leads to a reduced life span.  Heterozygosity causes enough hemoglobin to be produced to keep red blood cells healthy. Very common in Africa.  Stabilizing selection as heterozygosity infers less susceptibility to malaria. - One of leading causes of death in Africa.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Stabilizing Selection in Sickle-Cell Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Peppered Moths and Industrial Melanism Until the mid nineteenth century, Peppered Moths,Biston betularia, had predominately light-colored wings.  Subsequently, dark individuals became predominant. - Industrial smog helped turn lichens on tree trunks dark. - Contrasting colors between trunk color and moth color led to differential predation by birds.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Peppered Moths and Industrial Melanism Second half of the twentieth century saw widespread implementation of pollution controls, thus trends reversed and light colored moths again dominated. But, caution must be taken, as the selective agent could be some factor other than wing coloration.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Industrial Melanism Copyright © McGraw-Hill Companies Permission required for reproduction or display

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Species Concept A species is generally defined as a group of organisms unlike other such groups and does not integrate extensively with other groups in nature.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Species Formation Local populations adapt to the specific circumstances each faces. When they become different enough, the populations become ecological races. Natural selection reinforces differences through isolating mechanisms. Two races become incapable of interbreeding and are considered two separate species.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Prezygotic Isolating Mechanisms Prevent formation of Zygote:  Geographic Isolation  Ecological Isolation  Behavioral Isolation  Temporal Isolation  Mechanical Isolation  Prevention of Gamete Fusion

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Geographical and Ecological Isolation In Oaks

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Postzygotic Isolating Mechanisms Prevent zygotes from developing into normal, functional offspring.  Improper development - Reduced fertility or sterility.

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Review Gene Variation Pace of Evolution  Fossil Record  Molecular Record  Anatomical Record Hardy-Weinberg Forms of Selection Industrial Melanism Species Formation

Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies Copyright © McGraw-Hill Companies Permission required for reproduction or display