Honors Biology Reading Guide Chapter 13 v Lamarck Ø Suggested fossils/organisms differed because species evolve Ø Proposed species evolve as a result of interactions with their environment v Wallace Ø Hypothesis almost identical to Darwin v Lyell Ø Natural forces gradually changed earths surface still operating in modern times v Malthus Ø Human suffering was the consequence of human populations increasing faster than food supplies and other resources = struggle for existence, best survive v Artificial selection Ø The selective breeding of domesticated plants and animals to promote the occurrence of desirable traits v Natural selection Ø A process in which individuals which certain inherited traits were more likely to survive and reproduce than individuals that do not have these traits v Descent with modification Ø Present day species arose from a succession of ancestors v Adaptation Ø An inherited characteristic that enhances an organisms ability to survive and reproduce n a particular environment v Mutations are random and rare events v Natural selection is not random v What heritable character changes in the pocket mouse Ø Fur color Light to dark v What trait is selected for Ø Black lava dark colored fur v Why/how Ø Predators could see the light mouse Ø More survived to adulthood that were dark furred and reproduced v Natural selection examples Ø Finches change in beak size, there used to be lots of small seeds but hen it got dry and the larger seeds were more abundant, so more birds with larger beaks survived Ø Pesticide resistance at first a lot of the insects die, but those that survive are resistant and reproduce v In what sense is natural selection more an editing process than a creative process Ø Does not create alleles rather an event/the environment leads to natural selection for that organism already in the population that have those alleles v Evidence of evolution Ø Fossil record
Ø Biogeography Ø Anatomy Ø Molecular biology v Population Ø A group of individuals belonging to one species and living in the same geographic area v Gene pool Ø All the alleles for all the genes in the population v Microevolution Ø A change in a populations gene pool over generations v Why cant individuals evolve Ø Natural selection acts on individuals each individuals combination of traits affects its survival and reproductive success Ø But evolutionary impact of natural selection is only apparent in the changes in a population or organisms over time v Mutations duplication of a gene of small pieces of DNA through errors in meiosis can provide an important source of genetic variation v Mutation rates in animals an plants average on in every 100,000 genes per generation v Long time spans between generations and diploid genomes prevent most mutations from significantly affecting genetic variation from one generation to the next v In prokaryotes mutations can quickly generate genetic variation because they are haploid v In organisms that reproduce sexually most of the genetic variation in population results form the unique combinations of alleles that each individual inherits Ø Crossing over Ø Independent assortment/orientation Ø Random fertilization v Genetic variation is necessary for a population to evolve but variation alone does not guarantee that microevolution will occur v The Hardy- Weinberg equation can test whether a population is evolving v p frequency dominant allele v q = frequency of recessive allele v 2pq = frequency of both alleles v p + q = 1 v Genetic drift Ø A change in the gene pool of a population due to chance events of genetic drift are most pronounced in small populations Ø Bottleneck effect genetic drift resulting form a drastic reduction in population size the resulting population is no longer genetically representative of the original population v Founder effect Ø Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool is not reflective of the original population
v Relative fitness Ø The contribution an individual makes to the gene pool o the next generation relative to the contributions of other individuals in the population v Struggle for existence Ø Competition for resources needed to live v Survival of the fittest Ø Continued existence of organisms better adapted to their environment v Phrase survival of the fittest differs from the biological definition of relative fitness Ø Survival alone does not guarantee reproductive success an organisms relative fitness is determined y its number of fertile offspring and thus is relative to the contribution to the gene pool of the next generation v Natural selection can alter variation in a population in three ways Ø Stabilizing selection Natural selection that favors intermediate variants by acting against extreme phenotypes Ø Directional selection Natural selection in which individuals at the end of the phenotypic range survive and reproduce more successfully than do other individuals Ø Disruptive selection Natural selection in which individuals on both extremes o the phenotypic range are favored over intermediate phenotypes v Sexual selection Ø A form of natural selection in which individuals with certain inherited traits are more likely than other individuals to obtain mates Example reproductive organs v Sexual dimorphism Ø Marked differences between the secondary sex characteristics of males and females Size difference v Intrasexual selection Ø Within the same sex Usually males Ø In some species individuals compete directly with members of the same sex for mates Moose v Intersexual selection Ø Between sexes or mate choice individuals of one sex (usually the female) are choosy between mates Peacock v Balancing selection Ø Natural selection that maintains stable frequencies of two or more phenotypic forms in a population v Heterozygote advantage Ø Greater reproductive success of heterozygous individuals compared to homozygotes tends to preserve variation in gene pools
v Frequency dependent selection Ø Selection in which the fitness of a phenotype depends on how common the phenotype is in a population Scale eating fish with right/left mouths v Natural selection doesn t make perfect organisms Ø Natural selection can only occur from mutations that occur which wont necessarily be the best trait possible Ø Evolution only acts on traits the organism already has Ø Adaptations means compromise Ø Mutations are chance Events Environment Can change gene pool and exterminate helpful alleles