Bio 2: Exam 1

7 characteristics of life

Respond to stimuli, homeostasis, cellular organization, reproduction, process energy (ATP), evolve, heredity

Homeostasis

Maintenance of stable internal conditions within an organism

Adaptation

Any modification that makes an organism better suited to its way of life

Descent with modification

Darwin's phrase for evolution: populations change over generations, producing heritable traits that aid survival/reproduction

Vertical descent

Transfer of genes from parent to offspring

Horizontal gene transfer

Transfer of genetic material between organisms that are not parent and offspring

Structure determines function

Principle that biological structures arise as a species adapts to its environment

Reducing Atmosphere Hypothesis

Oparin & Haldane's idea that a primitive, oxygen-poor atmosphere plus an energy source spontaneously formed organic monomers

Oparin and Haldane

1920s scientists who proposed the Reducing Atmosphere Hypothesis

Miller-Urey experiment

1953 experiment showing amino acids, sugars, and nitrogen bases can form from primitive atmospheric gases plus an energy source

Extraterrestrial Hypothesis

Idea that organic carbon was delivered to early Earth by asteroids/comets (evidence: carbonaceous chondrite meteorites)

Deep-Sea Vent Hypothesis

Idea that organic monomers formed where superheated, mineral-rich vent water meets cold seawater

Clay Hypothesis

Idea that clay/mineral surfaces acted as a workbench, helping monomers polymerize into chains

Protobiont

A membrane-enclosed collection of polymers with crude self-replication; cell-like but not yet alive

RNA World

Early stage where RNA both stored genetic information and catalyzed reactions, before DNA and proteins took over

Ribozyme

An RNA molecule capable of catalyzing chemical reactions

DNA/RNA/Protein World

Stage where DNA took over information storage and proteins took over catalysis/structure, replacing the RNA World

Stromatolites

Fossilized mats of mineralized cyanobacteria; evidence of very early life

Fossil

Remains or traces of past life

Paleontology

The study of the fossil record

Stratum

A recognizable layer of rock formed from sediment, used to date fossils in relative sequence

Index fossil

A common, easily identified, broadly distributed fossil present only during a known time span; used for relative dating

Half-life

The time required for half the atoms of a radioactive isotope to decay into another element

Radiometric dating

Absolute dating method using the known, constant half-life of radioactive isotopes

Precambrian Time

Earliest span of geologic time (4,500-600 mya), about 87% of all geologic time; first cells, cyanobacteria, eukaryotes (~2 bya), multicellularity (~1.5 bya)

Endosymbiotic Hypothesis

Proposed explanation for the evolutionary origin of eukaryotic cells/multicellularity

Ediacaran Period

600-540 mya; first multicellular animals (e.g. sponges) appear; ends in a mass extinction

Cambrian Explosion

~543-490 mya; period when essentially all existing animal phyla first appear in the fossil record

Pangaea

The supercontinent formed during the Permian period by continental drift

K-T extinction

Mass extinction ending the Cretaceous period (killed the dinosaurs), caused by a meteorite impact plus volcanism

6th Mass Extinction

The ongoing, human-caused (Holocene/Anthropocene) extinction event happening today

Human ancestral lineage

Australopithecus to Homo habilis to Homo erectus to Homo sapiens

Neanderthals and Denisovans

Non-ancestral side branches of human evolution; not direct human ancestors

Scala Naturae

Aristotle's "Great Chain of Being," ranking life from simple to complex with humans at the top

Carolus Linnaeus

Creator of binomial nomenclature; believed in the fixity of species

Catastrophism

Cuvier's idea that local catastrophes caused later rock strata to contain new mixes of fossils

Lamarckianism

Lamarck's theory of inheritance of acquired characteristics

Uniformitarianism

Charles Lyell's idea that the same gradual geological processes seen today have always operated; gave Darwin the timescale evolution needed

Struggle for existence

Malthus's concept that reproductive potential exceeds what the environment can support, forcing competition

Darwin's observations and inferences

The logical chain (fertility, population stability, limited resources, variation, heritability) that leads to the inference of natural selection

Biogeography (Darwin's observation)

Darwin's observation that similar species occupy similar habitats, suggesting related species are modified according to environment

Adaptive melanism

Rapid shift in coat/body color due to natural selection (example: rock pocket mouse)

Industrial melanism

Shift in peppered moth coloration from light to dark due to industrial pollution darkening tree trunks

Homologous structures

Structures that are similar because of shared common ancestry

Vestigial structures

Reduced, functionless remnants of ancestral structures (examples: human appendix, tailbone, wisdom teeth)

Convergent evolution (analogy)

Similar traits evolving independently in unrelated lineages due to similar environmental pressures

Ontogeny recapitulates phylogeny

Haeckel's phrase describing shared features in vertebrate embryonic development as evidence of common ancestry

Cytochrome c

A highly conserved protein used to measure evolutionary relatedness via amino acid sequence differences

Monomorphic gene

A gene where about 99% of the population carries one allele

Polymorphic gene

A gene with 2 or more alleles present in the population

SNP (single nucleotide polymorphism)

The smallest and most common type of mutation: a change in a single nucleotide

Allele frequency

Number of copies of a specific allele divided by the total number of alleles for that gene in the population

Genotype frequency

Number of individuals with a given genotype divided by the total number of individuals in the population

Hardy-Weinberg Principle

States that allele and genotype frequencies stay constant across generations if 5 conditions are met: no mutation, no gene flow, random mating, no genetic drift, no selection

Hardy-Weinberg equation

p + q = 1, and p squared + 2pq + q squared = 1

Microevolution

Change in allele frequencies within a population over time

Genetic mutation (cause of microevolution)

Random, non-goal-directed change that creates new alleles; the ultimate source of new variation

Gene flow

Movement of alleles between populations via migration; reduces genetic divergence between populations and increases diversity within one

Assortative mating

Non-random mating where individuals with similar phenotypes pair up, increasing homozygosity

Disassortative mating

Non-random mating where individuals with dissimilar phenotypes pair up, increasing heterozygosity

Inbreeding

Mating between genetically related individuals, increasing expression of recessive alleles

Genetic drift

Random, chance-based changes in allele frequency; effect is stronger in small populations

Bottleneck effect

Genetic drift following a sharp population crash, reducing genetic variability (examples: cheetahs, northern elephant seals)

Founder effect

Genetic drift that occurs when a new population is started by a small number of individuals

Requirements for natural selection

Variation, inheritance, differential adaptiveness, differential reproduction

Directional selection

Selection that shifts a trait distribution toward one extreme (example: antibiotic-resistant bacteria)

Stabilizing selection

Selection favoring intermediate phenotypes over both extremes (example: human birth weight)

Disruptive (diversifying) selection

Selection favoring both extremes over the intermediate phenotype (example: Cepaea snails)

Balancing selection

Selection that actively maintains multiple alleles in a population over time

Heterozygote advantage

Balancing selection where the heterozygous genotype has higher fitness than either homozygote (example: sickle-cell trait and malaria resistance)

Negative frequency-dependent selection

Selection where a phenotype's fitness decreases as it becomes more common

Sexual selection

Selection for traits that increase mating success; can be intrasexual (same-sex competition) or intersexual (mate choice)

Macroevolution

Evolutionary changes producing new species or groups of species, from accumulated microevolution over long time spans

Biological Species Concept

Defines a species as a reproductive community of interbreeding populations, reproductively isolated from other such groups

Prezygotic isolating mechanisms

Barriers that prevent mating attempts: habitat, temporal, behavioral, mechanical, and gamete isolation

Postzygotic isolating mechanisms

Barriers that prevent viable/fertile hybrid offspring after mating: hybrid inviability, hybrid sterility, hybrid breakdown

Allopatric speciation

Speciation caused by geographic isolation interrupting gene flow between populations

Sympatric speciation

Speciation without geographic isolation, often caused by polyploidy

Adaptive radiation

Rapid diversification of one ancestral species into many species filling different niches (examples: Darwin's finches, Hawaiian honeycreepers)

Phyletic gradualism

Model where speciation occurs gradually and transitional fossils are found

Punctuated equilibrium

Model where speciation occurs rapidly after long periods of stasis, with few transitional fossils found

Systematics

The scientific study of classifying organisms and their evolutionary relationships

Taxonomy

The practice of naming, identifying, and classifying organisms

Binomial nomenclature

Two-part scientific naming system (genus plus specific epithet) created by Linnaeus

Taxonomic hierarchy

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Clade

A group consisting of a common ancestor and all of its descendants

Phylogenetic tree

A diagram showing evolutionary lines of descent, with branch points representing divergence from a common ancestor

Homology (in taxonomy)

Similarity between organisms due to shared common ancestry

Parallel evolution

Independent evolution of similar traits starting from a similar ancestral condition

Molecular clock

Method that uses the assumed constant rate of neutral mutation to estimate how long ago two species diverged

Cladistics

Classification method that uses only shared derived characters to build cladograms

Parsimony (Occam's razor, cladistics)

Principle that the arrangement requiring the fewest assumed evolutionary changes is preferred

Monophyletic group

A group containing a common ancestor and ALL of its descendants

Paraphyletic group

A group containing a common ancestor but NOT all of its descendants

Polyphyletic group

A group whose members trace to separate ancestors, excluding the group's true common ancestor

Three-Domain System

Classification system consisting of Domain Bacteria, Domain Archaea, and Domain Eukarya

Charles Darwin

Naturalist who proposed natural selection as the mechanism of evolution, based on observations from the HMS Beagle voyage

Alfred Russel Wallace

"Father of Biogeography"; independently proposed the theory of natural selection

Thomas Malthus

Economist whose ideas on population and limited resources influenced Darwin's concept of the struggle for existence