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.