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4581306
Evolution
Beschreibung
ib biology 5.1,2
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biology
evolution
ib
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Zusammenfassung der Ressource
Evolution
Evidence
Fossil Records
Sequence of changing fossils from layers of rock strata
Carbon dating (radioisotopes)
Phylogenic tree can be made
e.g. Equus
(-) Gaps in records
fossils only form in environments that prevent decay
Selective Breeding
Breed differentiation has occurred in domesticated animals
(-) Human rather than natural selection
Evolution in short time-period
e.g. Dogs
Structures
Homologous Structures (Divergent Evolution)
Similar structure, different function
Often formed similarly in embryo
e.g. Pentadactyl limb
same bones in similar positions "unity of type" - Darwin
i.e. radius and ulna attached to humerus
“Adaptive radiation”
different purposes
swimming, running, digging, jumping
Rudimentary/vestigial organs
e.g. human appendix, snake hip bones
Analogous Structures (Convergent Evolution)
Similar function, different origin
e.g. fish and whale tails
Patterns of Variation
Continuous variation
across geographical range
e.g. human skin colour
Discrete variation
e.g. industrial melanism
therefore, causes divergence
Speciation
Divergence in the gene pool of a population
can be confirmed if two diverged populations are merged and do not interbreed
Models
Phyletic Gradualism
many intermediate forms between species
Punctuated Equilibrium
long periods of relative stability (stasis) and then periods of rapid evolution
Mass speciation event - natural disaster causes extinction and new species can erupt to take advantage of resources
explains gaps in fossil records
incited by sudden environmental changes
e.g. Galapagos finches
Gradualism: Darwin observes Adaptive radiation
Punctuated Eq.: Peter and Rosemary Grant observed drought
in drought, bigger beaks survived
Directional natural selection
Causes
Change in allele frequencies in populations
Gene pools contain all the genes and the different alleles of a population
Theoretical: Hardy-Weinberg Equilibrium formula
Actual: ALFreD database
Genetic equilibrium - when all members of a population have an equal chance of contributing to the future gene pool i.e. same chance of reproduction
Heritability is the proportion of variation that is due to genes
Reproductive Isolation
Sympatric
Temporal
e.g. flowering at different time
Behavioral
e.g. mating displays change
Allopatric
Geographical
i.e. no interaction with other populations
esp. Endemic species
Polyploidy
Causes
Autopolyploidy
single species, problem in meiosis
Allopolyploidy
hybrid
Organism that has more than two sets of homologous chromosomes
diploid and haploid gamete fuse
organism not sterile since there will always be a chromosome to pair with if it mates with another polyploid or self-pollinates
Effects
Instant speciation when only polyploids can reproduce together
evolution for angiosperms that clone themselves
e.g. Allium
desirable crops can self-pollinate
e.g. Red viscacha has 102 chromosomes, 4n=112 then shed some
Mechanisms
Natural Selection
Patterns of Natural Selection
Stabilizing selection
mean of the normal curve is preferred
e.g.. birth size of humans, # of eggs hatched
Directional selection
shift to one extreme due to a selective pressure or environmental resistance
e.g.peppered moths, beak sizes, antibiotic resistance
mutations occur that make the bacteria resistant to antibiotics
exchanging of plasmids
Disruptive selection
the mean is undesirable
tends to drive speciation most because offspring occupy divergent niches
e.g. Red crossbill, small or large fish
i.e. competition
Causes
variation within a species
Mutations
meiosis (independent assortment, crossing over)
sexual reproduction and random fertilization
plasmid transfer
populations produce more offspring than an environment can support
environmental resistance
survival of the fittest
Effects
adaptation to make an individual more suited to its environment
occupies a niche
Only animals that reproduce pass on their genes to offspring
Natural selection increases the frequencies of beneficial alleles
"progressive change"
Organisms that reproduce more often evolve faster
Genetic Drift
i.e. geographical separation
Genetic Flow
i.e. migration of populations
Selective Pressures
i.e. extenuating factors
The cumulation of changes in the heritable characteristics of a population
Medienanhänge
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