Unit 7: Natural Selection Flashcards
natural selection
- due to variation in population and competition for resources
- organisms with more favorable trait are more likely to survive and reproduce, passing their traits onto the next generation
artificial selection
- organisms with certain traits are bred until population has the trait
- humans affect variation
types of selection
disruptive, stabilizing, directional
disruptive selection
selection for two extreme phenotypes and against intermediate phenotype
stabilizing selection
selection for intermediate phenotype and against two extreme phenotypes
directional selection
selection for AN extreme phenotype and against all other phenotypes
five conditions of h-w equilibrium
- large population
- random mating
- no mutations
- no genetic flow
- no natural selection
genetic drift
- random allele frequency changes
- reduces population size
- can decrease genetic diversity, either making harmful alleles fixed (constant) or removing harmful alleles
- founder’s effect and bottleneck effect
founder’s effect
small population is isolated from original population, causing certain alleles to be over/underrepresented
bottleneck effect
population is reduced by natural disaster - no selection based on traits (certain alleles can be over/underrepresented)
h-w equilibrium: “p”
frequency of dominant allele; 2AA + Aa/2 x # individuals
h-w equilibrium: “q”
frequency of recessive allele; 2aa + Aa/2 x # individuals
h-w equilibrium: “p^2”
frequency of homozygous dominant; #AA/total
h-w equilibrium: “2pq”
frequency of heterozygous; #Aa/total
h-w equilibrium: “q^2”
frequency of homozygous recessive; #aa/total
did the population evolve?
if allele/phenotype frequency has changed, the population has evolved
biochemical evidence of evolution
DNA or protein; comparison of number of differences
morphological evidence of evolution
homologous structures, ancestral/derived traits
homologous structures (homology)
similar structures due to common ancestry
ancestral/derived traits
traits derived from ancestor or from descendants
analogous structures
similar structures due to convergent evolution
types of prezygotic isolation
behavioral, temporal, geographic, habitat/ecological, mechanical, gametic
types of postzygotic isolation
reduced hybrid viability, reduced hybrid fertility, hybrid breakdown
hybrid breakdown
hybrid becomes less and less viable and fertile with each generation
speciation
creation of new species; sympatric and allopatric
sympatric speciation
- new species created from surviving ancestral species, WHILE both continue to inhabit the same region
- causes: habitat isolation, behavioral isolation, sexual selection, polyploidy
allopatric speciation
when biological populations of the same species become isolated due to geographic changes (geographical isolation)
homology
characteristics in related species can have underlying similarity even though functions may differ
embryonic homologies (homology)
similar early development
vestigial organs (homology)
structures with little/no use
molecular homologies (homology)
similar DNA and amino acid sequences
convergent evolution
distantly related species can resemble one another (similar problems, similar solutions); this similar evolution is NOT because of a recent common ancestor
analogous structures
- proof of convergent evolution
- similar structures that function in similar environments
biogeography
geographic distribution of species
endemic species
species found at a certain geographic location and nowhere else
last universal common ancestor (LUCA)
- ancestor of bacteria, eukarya, and archaea
- cellular organism that had a lipid bilayer and used DNA, RNA, and protein
monophyletic group
common ancestor + all of its descendants
paraphyletic group
common ancestor + SOME of its descendants
polyphyletic group
organisms grouped together but are not closely related
common ancestry of all life forms (conserved across 3 domains)
- DNA & RNA carry genetic info
- universal genetic code (codons to amino acids)
- conserved metabolic pathways
conserved elements in eukaryotes
cytoskeleton, membrane-bound organelles, linear chromosomes, endomembrane systems
horizontal gene transfer
- movement of genes between different domains
- exchange of transposable elements, plasmids, viral infections, fusion of organisms
microevolution
change on smallest scale; change in allele frequencies in a population over generations
source of genetic variation
mutations
- mutations in gametes passed to offspring
- point mutations
- chromosomal mutations –> gene duplication
- fast reproduction: mutations can quickly generate variation
sexual reproduction: shuffle existing alleles (crossing over, etc.)
fixed allele
all members of a population are homozygous for the same allele; more fixed alleles = less genetic diversity
hardy-weinberg equilibrium
frequencies of alleles and genotypes in a population’s gene pool remain CONSTANT over generations unless acted upon by agents other than sexual recombination
three major mechanisms of evolution
natural selection, genetic drift, gene flow
natural selection IN microevolution…
causes differential reproductive success
genetic drift IN microevolution
unpredictable fluctuation of alleles from one generation to the next
gene flow IN microevolution
population loses/gains alleles due to immigration or emigration
balancing selection
- diploidy: inherit 2 alleles; recessive allele is hidden in heterozygotes
- heterozygote advantage: heterozygotes have better survival
sexual selection
certain individuals more likely to obtain mates; intrasexual and intersexual selection
intrasexual selection
competition within same sex
intersexual selection
mate choice
natural selection canNOT fashion perfect organisms
- selection can only edit existing organisms
- evolution is limited by historical constraints
- adaptations are often compromises
- chance, natural selection, and the environment interact
macroevolution
evolutionary change above species level (cumulative effects of speciation over long periods of time)
reproductive isolation
processes that prevent interbreeding across species; prezygotic isolation and postzygotic isolation
hybrid zones
incomplete reproductive barriers; effects: reinforcement, fusion, stability
fusion
breakdown of reproductive barriers (if hybrid is as fit as parents)
reinforcement
strengthening of reproductive barriers (if hybrid is less fit than parents)
stability
no change in reproductive barriers
gradualism (speciation)
common ancestor; slow, constant change
punctuated equilibrium (speciation)
long periods of stasis punctuated by sudden change seen in fossil record
how did life arise?
- small organic molecules were synthesized
- small molecules –> macromolecules
- molecules packaged into protocells (membrane-containing droplets)
- self-replicating molecules allow for inheritance
“RNA world”
first genetic material was likely RNA; first catalysts were ribozymes (RNA)
synthesis of compounds on early earth
- early atmosphere: H2O vapor, N2, CO2, H2, H2S, methane, ammonia
- energy: lightning & UV radiation
- conditions favored synthesis of organic compounds: a primitive soup
endosymbiont theory
- mitochondria and plastids (chloroplasts) formed from small prokaryotes living in larger cells
- evidence: replication by binary fission; singular, circular DNA; ribosomes to make proteins; enzymes similar to living prokaryotes; two membranes
effect of continental drift/pangaea
movement of continental plates change geography and climate on earth, which leads to speciation and extinction
mass extinctions =
diversity of life
major periods in earth’s history END with
mass extinctions
major periods in earth’s history START with
adaptive radiations
major events during precambrian era
photosynthesis, atmospheric O2; eukaryotes
major events during paleozoic era
plants invade land, many animals appear; Permian extinction (-96% species)
major events of mesozoic era
formation of Pangaea; Cretacious Extinction (asteroid)
major events of cenozoic era
primates!
adaptive radiations
- many species arise from single common ancestor
- occurs when organisms make way to new, distant areas (allopatric speciation) or when environmental change causes extinctions which opens up new niches for survivors
evo-devo
evolutionary + developmental biology; evolution of new forms results from changes in DNA or regulation of developmental genes
heterochrony
evolutionary change in rate of developmental events
homeotic genes
master regulatory genes determine location and organization of body parts
