Studied by 8 peopleEvidence of evolution: Fossil records
Fossils found in rock layers (strata) allow us to determine geological areas from which organisms belong and gives a timeline for life on earth
Most found fossils do not exactly match current species: indicating life changed over time
Radiometric techniques to date fossils
The ratio of isotopes present in fossils is determined
C-14 is a parent atom to N-14, the daughter atom. The half-life of C-14 is known (5730 yrs), so the ratio between these two atoms can be used to communicate how old the fossil is
Fossil records direct evidence for evolution
Direct evidence: Body fossils that provide direct evidence of ancestral forms and include bones, teeth, shells, leaves, etc.
Can be preserved remains (soft tissue preserved) or petrified fossils, casts, molds (mineralised structures or preserved imprints)
Fossil records indirect evidence for evolution
Trace fossils which provide information about ancient life
Includes preserved footprints, burrows, coprolite (feces)
Limitations of fossil records as evidence for evolution
The fossil record is incomplete
Very specific conditions are required for the mineralization process for fossilization to take place
Generally only hard parts of organisms preserved
Fossils can be easily damaged, often it is only fragments recovered
Transitional fossils
They establish the connection between species by exhibiting traits common to both an ancestor and its predicted descendants.
eg. archaeopteryx connects dinos and birds
Law of fossil succession
The age of the fossil is equal to the age of the strata it is found in
The ordered succession of fossils suggests that newer specues likely evolved as a result of changes to ancestral species
Homologous structures
anatomical features found in different species that are similar in structure but may have a different function
Suggests a common ancestor; the structure may have evolved to be fit for the environmental conditions of different species
eg. the pentadactyl limb is similar in structure (5 finger-like structures)a mong humans, birds/bats, horses, and whales/dolphins, but with different functions; tool manipulation, wings for flying, hooves for galloping, fins for swimming
Adaptive radiation
several new species diversify from an ancestral source, with each new species adapted to utilise a specific unoccupied niche
Divergent evolution
a species diverges significantly and can no longer reproduce with organisms of original species, then a new species is declared (speciation)
Vestigial structures
Homologous features that no longer serve their original purpose — provide evidence for common ancestry
May be unused or used for a different purpose
eg. the human appendix
Analogous structures
anatomical features that are different in structure but have a similar function
May have confused earl evolutionary biologists as they may have though some species were more related than they are (no close common ancestor)
Supports convergent evolution
Convergent evolution
species living in similar environments may evolve to have similar adaptations in order to survive/thrive
Evidence for evolution: Selective breeding
when humans control the breeding of plants/animals, significant changes can occur in the gene pool over a short period of time
Supports evidence that species would change when the environment favoured organisms that could survive and breed
NOTE evolution is often slow, but some genes have a greater effect on change
Biochemical evidence of evolution
Organisms with similar DNA/amino acid sequences are more closely related
Cytochrome C (protein) is often used to compare because of its universality
Continuous variation
continuous variation in features across geographical ranges supports the concept of gradual divergence —species change slowly and constantly
Industrial melanism
peppered moths exist in a light form and dark form. The dark form has increased in population since the Industrial Revolution since pollution and soot turns lichen and trees black. Evolved to be better at camoflouge
Overproduction of offspring
Species tend to produce more offspring than the environment can support to maximize chances of offspring surviving and therefore not all individuals can survive to maturity
Limited nutrient supply, space, sunlight, etc.
Leads to competition and struggle
Causes of variations in genotypes/phenotypes
mutations (nonsense or missense)
meiosis (crossing over/recombination and random assortment of homologous chromosomes)
sexual reproduction (random fertilization by the egg and sperm will always generate different zygotes)
Beneficial alleles
if they lead to a trait that allows species to survive and reproduce in their environment, their frequence increases in a population over time
Mutations caused by…
spontaneous replication errors or induced errors by mutagens (chemicals, viruses or radiation)
they are not formed based on need!!
Requirements for a mutation to result in a new allele/variation
mutations must be in the gamete because mutations in somatic cells are not heritable
therefore must occur during meiosis or be passed down from parents
must be in coding DNA
Why do harmful mutations often die out
If it results in a selective disadvantage an organism may not be able to survive and reproduce
Genetic variety in asexually reproducing populations
relies on mutation or horizontal gene transfer (eg. plasmids exchanged between prokaryotes)
Adaptations
changes in the traits of a population due to variations and selective pressures
they are unconscious and made by populations not individuals
Steps of evolution by natural selection
overproduction of offspring: genetic variation in this population leads individuals with useful variations to succeed and individuals with harmful variations find it more difficult to survive
Individuals that are of better “fitness” to the environment reproduce and pass on successful genetic characteristics while, due to struggle, individuals not fit to the environment likely die off
Over many generations, the accumulation of changes in heritable characteristics cause change in the gene pool ie. evolution occurs
Struggle
stresses (inter or intra species) may select for or against certain traits
Natural selection: Pesticide resistance in rats
pesticides wipe out all but a few genetically distinct resistant rats
those rats reproduce and thrive bc little competition
now there is a largely pesticide resistant rat population
Natural selection: Antibiotic resistance in bacteria
most bacteria are killed off by antibiotics so the patient improves, but one resistant bacterium remains bc of a modification to its genetic makeup
it multiplies by binary fission, can make the patient sick again
The same antibiotic will not affect the new bacteria population
Gene pool
all the genetic information present in the reproducing members of a population at a given time
large gene pools tend to have a greater variety of traits (opposite is true with small gene pools)
Inbreeding
practise of having closely related organisms mate, often results in small gene pools
Allele frequency
measure of the proportion of a specific variation of a gene in a population
not the same as the proportion of individuals with a trait
can be changed by immigration and emigration (ie. gene flow)
Disappearing alleles
due to the death of organisms with the allele because of natural, artificial, or sexual selection
Genetic drift
change in the composition of a gene pool as a result of chance or random events
faster and more significant in smaller populations where chance events have a bigger impact on gene pool
larger population less affected by random events and maintain more stable allele frequences with low genetic drift
Mechanisms and effects of reducing a large population to a smaller population
Mechanisms are population bottlenecks and founder effect
changes the allele frequencies of a population significantly
Population bottlenecks
occurs when a naturally occurring or human-induced event reduces a population by more than 50%
surviving population has less genetic variability so subject to a higher level of genetic drift
the population descended from the surviving members will have a different gene pool to original population
Founder effect
occurs when a small group breaks away from a larger population to colonize a new territory
this population subset does not have the same degree of diversity as the original larger population, therefore it is more subject to genetic drift
as this new colony increases, it will have a unique gene pool to original population
differs from population bottleneck because the original population remains intact
Stabilising selection
intermediate phenotype favoured over both extremes
operates when environmental conditions are stable and competition is low
eg human birth weights
Directional selection
one phenotypic extreme selected at the cost of the other phenotypic extreme
operates in response to gradual/sustained changes in environmental conditions
typically followed by stabilising selection once an optimal phenotype has been normalised
eg. antibiotic resistant bacteria populations
Disruptive selection
both phenotypic extremes favoured at the cost of the intermediate
results in bimodal spread
occurs when fluctuating conditions favour the presence of two different phenotypes
continued separation may lead to speciation
eg black or white moths in regions of sharply contrasting colour extremes
Isolation barriers
when a barrier prevents two populations from interbreeding and therefore keeps their gene pools separate
Prezygotic isolation
occurs before fertilisation can occur — no offspring are produced
Postzygotic isolation
occurs after fertilisation — offspring are either not viable or infertile
Temporal isolation
two populations differ in their periods of activity or reproductive cycles
eg. if species reaches sexual maturity at different times of the year
Behavioural isolation
when the presence or absence of a specific behaviour prevents reproduction from taking place
usually because two populations exhibit different specific courtship patterns
Geographical isolation
leads to allopatric speciation (speciation caused by geographic barriers)
two populations occupy different habitats or separate niches within a common region
or a geographical barrier prevents reproduction
Effect of polyploidy on evolution
quickly leads to speciation since the previous generation will be incompatible with the new generation
interbreeding can no longer occur since they have more than two full sets of chromosomes (triploidy=3n)
Eg. many allium species have diversified via polyploidy
Phyletic gradualism
a model of speciation that predicts that speciation occurs uniformly via steady and gradual transformation of whole lineages
big changes result from cumulative small changes
supported by gradual change in horse fossil records
Punctuated equilibrium
a model of speciation that predicts that species remain stable for long periods before undergoing abrupt rapid changes
seen as a periodic process
changes may be in response to drastic ecological events
supported by lack of transitional fossils for many species
Binomial nomenclature system
Genus species - underlined or italics
Point of binomial nomenclature
allows for identification and comparison of organisms based on recognised characteristics
shows how closely related organisms are, allowing for prediction of evolutionary links
makes it easier to collect/sort/group information
Three domains
Eukarya: eukaryotic organisms
protista - anamalia - plantae - fungi
Archaea: prokaryotic cells lacking a nucleus, often extreomphiles
eg. methanogens, thermophites
Eubacteria: prokaryotic cells lacking a nucleus and consisting of the common pathogenic forms
Taxa in order of increasing specificity
Kingdom - phylum - class- order- family - genus - species
Artificial classification
Grouping organisms based on superficial characteristics, without considering their evolutionary relationships or genetic similarities
Strength is they are easily recognisable
Flashcard: Natural Classification
A system of organizing and grouping organisms based on their evolutionary relationships and shared characteristics, rather than on artificial criteria
shows evolutionary relationships and taxonomic levels
disadvantage: highly mutable, tends to change as new information if discovered
Phylogenetic classification
groups species based on shared DNA or amino acid sequences
List plant phylums
Bryophyta - Filicinophyta - Coniferophyta - Angiospermophyta
Bryophyta
no true leaves, roots or stems
no vascularization
reproduces by spores
anchored by rhizoids
eg. mosses
Filicinophyta
has leaves, roots, and stems
has vascularization
reproduces by spores
leaves are pinnate
eg. ferns
Coniferophyta
has leaves, roots, and stems
has vascularization
reproduces by seeds (cones)
has woody stems
eg. conifers
Angiospermophyta
has leaves, roots and stems
has vascularization
reproduces by seeds (fruit)
has fruit and flowers
eg. flowering trees
Invertibrates
do not have a backbone
Animalia subgroups
vertebrates and invertebrates
Invertebrates phylum
Porifera - Cnidaria - platyhelmintha - annelida - mollusca - arthropoda
Porifera
No body symmetry (asymmetrical)
No mouth or anus (have pores to facilitate the circulation of material)
May have silica or calcium carbonate-based spicules for structural support
No segmentation
Examples include sea sponges
Cnideria
Have radial symmetry
Have a mouth but no anus (single entrance body cavity)
May have tentacles with stinging cells for capturing and disabling prey
Examples include jellyfish, sea anemones and coral
Platyhelmintha
Have bilateral symmetry
Have a mouth but no anus (single entrance body cavity)
Have a flattened body shape to increase SA:Vol ratio and may be parasitic
Examples include tapeworms and planaria
Annelida
Have bilateral symmetry
Have a separate mouth and anus
Body composed of ringed segments with specialisation of segments
Examples include earthworms and leeches
Mollusca
Have bilaterial symmetry
Have a separate mouth and anus
Body composed of a visceral mass, a muscular foot and a mantle (may produce shell)
Examples include snails, slugs, octopi, squid and bivalves (e.g. clams)
Arthropoda
Have bilateral symmetry
Have a separate mouth and anus
Have jointed body sections / appendages and have a hard exoskeleton (chitin)
Examples include insects, crustaceans, spiders, scorpions and centipedes
Chordata
Have bilateral symmetry
Have a separate mouth and anus
Have a notochord and a hollow, dorsal nerve tube for at least some period of their life cycle
Examples include mammals, birds, reptiles, amphibians and fish (also invertebrate sea squirts)
Vertebrates classes
Fish - amphibian - reptile - birds - mammals
Fish
Covered in scales made out of bony plates in the skin
Reproduce via external fertilisation (egg and sperm released into the environment)
Breathe through gills that are covered with an operculum
Does not maintain a constant internal body temperature (ectothermic)
Amphibians
Moist skin, permeable to gases and water
Reproduce via external fertilisation (usually spend larval state in water, adult state on land)
Can breathe through skin but also possess simple lungs
Do not maintain a constant internal body temperature (ectothermic)
Reptiles
Covered in scales made out of keratin
Reproduce via internal fertilisation and females lay eggs with soft shells
Breathe through lungs that have extensive folding (increases SA:Vol ratio)
Do not maintain a constant internal body temperature (ectothermic)
Birds
Covered in feathers (made out of keratin)
Reproduce via internal fertilisation and females lay eggs with hard shells
Breathe through lungs with parabronchial tubes
Maintain a constant internal body temperature (endothermic)
Mammals
Skin has follicles which produce hair made out of keratin
Reproduce via internal fertilisation and females feed young with milk from mammary glands
Breathe through lungs with alveoli
Maintain a constant internal body temperature (endothermic)
Full classification of humans
Animalia - chordata - mammalia - primate - homonidae - homo - sapiens
Full classification of buttercups
Plantae - angiospermophyta - eudicotidae - ranunculales - ranunculae - ranunculus - acris
Polyploidy in allium
More common in plants - may lack separate sexes or be capable of self-pollination
other organsism would need 2 polyploid parents to be a fertile polyploid - must have an even number of n
allium can be triploidy, tetraploidy, → 8n
speciation can only occur if the polyploid is viable and fertile but cannot interbreed with the original population
Reclassification in taxonomy
species may be separated or grouped together in genera due to new evidence
eg. humans and chimps were placed into homonidae
Note
Flashcard