Unit 4 review chapters 22-23
• The Darwinian view of life was in contrast to the traditional beliefs of that time
• Natural selection-concept that says a population can change over generations in individuals w/heritable traits produce more viable offspring than others.
• Evolutionary adaptation-result of natural selection; accumulation of inherited char’s that enhance an organisms’ ability to survive & reproduce in specific environments
• Taxonomy-branch of biology for naming and classifying organisms
• Carolus Linnaeus-binomial nomenclature
• Fossils-sedimentary rock, remains of parts of organisms from the past
• paleontology-study of fossils
• Gradualism-geologic theory that states that profound changes in Earth’s features over the course of geologic time are the result of slow, continuous processes
• Uniformitarianism-geologic processes that have shaped the earth have not changed in earth’s history
Lamarck-early theory of evolution; acquired characteristics could be passed on
**characteristics acquired in an indiv’s lifetime cannot generally be passed on through genes
Descent w/modification-Darwin’s idea that all living organisms are related by descent from a remote common ancestor
• Both Darwin's & Lamarck's ideas regarding evolution included the interaction of organisms w/ their environment is impt in the evolutionary process.
Darwin’s theory of natural selection states:
1.) natural selection is the differential success in reproduction that results from the interaction b/w individuals that vary in heritable traits & their environment
2.) natural selection can produce an ↑ over time in the adaptation of organisms to their environ.
• 3.) if an environ changes over time, or if indiv’s of a particular spp move to a new environ, natural selection may result in adaptation to these new conditions, sometimes giving rise to new spp in the process
• Natural selection can only work on heritable traits
• Natural selection is based on:
• variation exists w/in populations• • the fittest individuals tend to leave the most
offspring• • there is differential reproductive success w/in
populations• • Pop’s tend to produce more indiv’s than the
environment can support
• One example of humans undergoing evolution is the event of the reduction of body hair
• Artificial selection-is when species are modified by humans (plants/animals are chosen to breed in order to maintain desired traits)
• Population-group of interbreeding indiv’s who live in a specific area (smallest unit that can evolve)
• The more similar 2 spp are the more recently they shared a common ancestor
• Over time many organisms lose many structures (some deep-sea fish lose their eyes, as well as cave bats, etc…) How does natural selection account for this?
• Under particular circumstances that persisted for long periods, each of these structures presented greater costs than benefits
• Darwin’s theory explains a wide range of observations; in living populations, homology, vestigial organs, molecular homologies, biogeography, & fossils
• Natural selection explains changes in living pop’s: ongoing evolution of bacteria and viruses
• Homology-related species share characteristics resulting from common ancestry (homologous structures)
• Vestigial organs-no longer much use
• Molecular homologies-shared charact. At the molecular level DNA
• Fossils-succession in the fossil record
• What are some examples of homologous structures?
• Variation in homologous structures can be explained by the variations in the development of the structures as the embryo’s grow
• Wings of a bat & arm of a human represent homology
• Wings of a bird & wings of an insect do not represent homology
• Biogeography-distribution of spp. (endemism)
• ex: spp in temperate S. America looked more like plants in tropical S. America than they did the plants in temperate Europe
• Alfred Wallace came to the same conclusions as Darwin while in Malaysia & so they came out with the “descent with modification” idea together
• Chapter 23
• Population genetics gives a foundation for studying evolution (pop change over time)
• Microevolution-smallest scale (change in pop’s from generation to generation)
• Modern synthesis-a comprehensive theory of evolution that integrates ideas from many fields, such as genetics, statistics, biogeography, & paleontology
• Gene pool-total aggregate of genes in a population at any one time (all alleles at all loci)
• Fixed allele-when all members of a population are homozygous for the same allele
**If the blending hypothesis was true then Members of a breeding pop should become more uniform in phenotype
• The hardy-Weinberg theorem that a population is not evolving at long as the gene frequency of a population is unchanging (Hardy-Weinberg equilibrium)
• p2 + 2pg +q2 = 1
• p2 = homozygous dominant
• Q2=homozygous recessive
• 2pq=heterozygous
• HW cond’s
• A pop will be in HW equilibrium if there is:
• a large pop,
• no migration,
• no mutation,
• no natural selection,
• & random mating occurs
• In a Hardy-Weinberg population w/ 2 alleles, A and a, that are in equilibrium, the frequency of allele a is 0.7. What is the % of the population that is homozygous for this allele?
• p + q = 1
• q=0.7
• q2 = 0.49
P.5
Q.5
p .5 q .5
P2
.25
pq.25
pq.25
q2.25
• Mutation & recombination provides the variation necessary for evolution
• New genes & alleles originate by mutations (changes in nt sequence of DNA); somatic cell mutations disappear when someone dies, only mutations in cells that make gametes are passed on
• **harmful recessive alleles in a sexual spp are usually found in indiv’s heterozygous for that allele
• Point mutations
• Chromosomal mutations
• Most genetic differences in a pop. are due to recombination; new combinations arise each generation
• Natural selection, genetic drift, & gene flow are 3 main factors that can alter a pop’s allele freq’s
• Indiv’s better suited to the environment tend to produce more offspring
• Genetic drift is an unpredictable fluctuation in allele freq’s from 1 generation to the next (ex: bottleneck effect, founder effect)
• Bottleneck effect: when a small isolated pop of organisms undergo some kind of event in which only a few indiv’s from the original pop survive;thus changing the allele freq’s of the new pop
• Founder effect—a few indiv’s become isolated from a larger pop establishing a new pop w/a diff gene pool
• Polymorphic-2 or more forms of a trait in a pop (different flower colors)
• Geographic variation-diff’s in gene pools, among pop’s or parts of pop’s
• Cline-graded change in a trait along a geographic axis (ex: a ↓ in size of plants as you ↑ in altitude)
• Heterozygous advantage are individuals that are heterozygous at a certain locus which gives them an advantage for survival (sickle cell disease)
• Fitness-contribution an organism makes to the gene pool of the next generation relative to the contributions of other members
• Ms. Douglas has a fitness of ZERO
• There are 3 modes of selection:
• Directional-one end or the other (fossils show that capybara’s have gotton smaller over time)
• Disruptive-favors low/high not median (a bug has 2 very diff color patterns)
• Stabalizing-favors median (a bird that produces 4-6 eggs per clutch)
• Sexual selection– natural selection for mating success (bright colored male birds get more chicks than duller colored birds)
• This can result in sexual dimorphism (big diff’s b/w sexes)
• Often, mature males are much larger than mature females. This size difference can be attributed to:
• male hormones having more effect on body size than female hormones do
• intrasexual selection
• females preferentially selecting larger males as mates
• Natural selection cannot produce perfection b/c:
• Evolution limited by historical restraints
• Adaptations are often compromises
• Chance & natural selection interact
• Selection can only edit existing variations
• Biologists are interested in preserving the diversity of living organisms on the planet.– Explain 3 of the following processes or
phenomena, using an appropriate example for each.
• -mutation
• -adaptive radiation
• -polyploidy
• -population bottlenecks
• -growth of human population
For a particular genetic locus in a population, the frequency of the recessive allele (a) is 0.4 and the frequency of the dominant allele is (A) 0.6
– What is the freq of each genotype AA, Aa, aa in this pop? What is the freq of the dominant phenotype?
– How can the H-W principle of genetic equilibrium be used to determine whether this pop is evolving?
– Identify a particular environmental change & describe how it might alter allelic freq’s in this pop. Explain which condition of the H-W principle would not be met.