Evolution Flashcards
Define biological evolution
A change in the allele frequency of a population’s gene pool over successive generations
How do fossils provide evidence for evolution?
The fossil record provides evidence by revealing the features of an ancestor for comparison against living descendants
What is the fossil record and what does it show?
The totality of fossils, both discovered and undiscovered, is referred to as the fossil record
The fossil record shows that over time changes have occurred in the features of living organisms (evolution)
What are fossils and what two categories can they be divided into? What different types of evidence may they provide?
A fossil is the preserved remains or traces of any organism from the remote past
Preserved remains (body fossils) provide direct evidence of ancestral forms and include bones, teeth, shells, leaves, etc.
Traces provide indirect evidence of ancestral forms and include footprints, tooth marks, burrows and faeces (coprolite)
Explain the law of fossil succession
his chronological sequence of complexity by which characteristics appear to develop is known as the law of fossil succession
This ordered succession of fossils suggests that newer species likely evolved as a result of changes to ancestral species
Explain how strata form and how this provides information on the sequence of development
Fossils can be dated by determining the age of the rock layer (strata) in which the fossil is found
Sedimentary rock layers develop in a chronological order, such that lower layers are older and newer strata form on top
Each strata represents a variable length of time that is classified according to a geological time scale (eons, eras, periods)
Define transitional fossils, explain the. significance and provide an example
Transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken by a single genus
They establish the links between species by exhibiting traits common to both an ancestor and its predicted descendents
An example of a transitional fossil is archaeopteryx, which links the evolution of dinosaurs (jaws, claws) to birds (feathers)
What may be a limitation to the use of fossils to evaluate evolutionary links?
Only the hard parts of an organism are typically preserved, meaning usually only fragments of remains are discovered
With limited fossil data, it can be difficult to discern the evolutionary patterns that result from ancestral forms
What may be a limitation to the use of fossils to evaluate evolutionary links?
Only the hard parts of an organism are typically preserved, meaning usually only fragments of remains are discovered
With limited fossil data, it can be difficult to discern the evolutionary patterns that result from ancestral forms
Define selective breeding and explain how it provides evidence for evolution
Selective breeding is a form of artificial selection, whereby man intervenes in the breeding of species to produce desired traits in offspring
By breeding members of a species with a desired trait, the trait’s frequency becomes more common in successive generations
Selective breeding provides evidence of evolution as targeted breeds can show significant variation in a (relatively) short period
Provide an example of selective breedng in the plant kingdom
Plants of the genus Brassica have been bred to produce different foods by modifying plant sections through artificial selection
This includes broccoli (modified flower buds), cabbage (modified leaf buds) and kale (modified leaves)
Provide two examples of selective breeding in the animal kingdom
Example 1: Horse Breeding
Horses have been selectively bred across many generations to produce variation according to a targeted function
Race horses have been bred for speed and hence are typically leaner, lighter, taller and quicker
Draft horses have been bred for power and endurance and hence are sturdier and stockier
Example 2: Cow Breeding
Cows have been selectively bred across many generations to produce offspring with improved milk production
Farmers have also targeted the breeding a cows with a mutation resulting in increased muscle mass
The resulting stock of cattle (termed Belgian Blue) have excessive bulk and produce more edible lean meat
Example 3: Dog Breeding
Dog breeds show an enormous amount of variety due to the targeted selection of particular traits by man
Hunting dogs (e.g. beagles) were typically bred to be smaller in stature so as to enter fox holes
Herding dogs (e.g. sheep dogs) were bred for heightened intelligence in order to follow herding commands
Racing dogs (e.g. greyhounds) were specifically bred to be sleek and fast
Toy dogs (e.g. chihuahuas) were selectively bred for their dimunitive size
How may comparing anatomy allow for ancestry to be established?
Comparative anatomy of groups of organisms may show certain structural features that are similar, implying common ancestry.
The more similar the homologous structures between two species are, the more closely related they are likely to be as the species would have had less time to evolve
What are homologous structures and how why does this occur?
Anatomical features that are similar in basic structure despite being used in different ways are called homologous structures
This occurs when species rapidly diversify from their common ancestor by adapting their function to a unique niche. This is known as adaptive radiation.
Discuss homologous structures with reference to an example
A classical example of homologous structures is the pentadactyl limb in a variety of different animals
Mammals, birds, amphibians and reptiles all share a similar arrangement of bones in their appendages based on a five-digit limb
Despite possessing similar bone arrangements, animal limbs may be highly dissimilar according to the mode of locomotion:
-Human hands are adapted for tool manipulation (power vs precision grip)
-Bird and bat wings are adapted for flying
-Horse hooves are adapted for galloping
-Whale and dolphin fins are adapted for swimming
Discuss divergence in species [ 4 marks ]
Within a population of any given species there will be genetic variation (i.e. variation which is inheritable) Typically this variation will be continuous and follow a normal distribution curve as the rate of change is gradual and cumulative
If two populations of a species become geographically separated then they will likely experience different ecological conditions Over time, the two populations will adapt to the different environmental conditions and gradually diverge from one another
The degree of divergence will depend on the extent of geographical separation and the amount of time since separation occurred
Populations located in close proximity that separated recently will show less variation (less divergence) Distant populations that separated a longer period of time ago will show more variation (more divergence)
How does speciation occur once species are geographically seperated ?
The degree of divergence between geographically separated populations will gradually increase the longer they are separated
As the genetic divergence between the related populations increase, their genetic compatibility consequently decreases
Eventually, the two populations will diverge to an extent where they can no longer interbreed if returned to a shared environment
When two populations can no longer interbreed and produce fertile, viable offspring they are considered to be separate species
Define speciation
The evolutionary process by which two related populations diverge into separate species is called speciation
Discuss evolution in connection to peppered moths
Peppered moths (Biston betularia) exist in two distinct polymorphic forms – a light colouration and a darker melanic variant
In an unpolluted environment, the trees are covered by a pale-coloured lichen, which provides camouflage for the lighter moth
In a polluted environment, sulphur dioxide kills the lichen while soot blackens the bark, providing camouflage for the dark moth
The frequency of the two different forms of peppered moth is dependent on the environment and evolves as conditions change
Before the industrial revolution, the environment was largely unpolluted and the lighter moth had a survival advantage
Following the industrial revolution, the environment became heavily polluted, conferring a survival advantage to the darker moth
Those possessing the advantage are more likely to survive and reproduce passing on the advantageous gene
What are the key component of natural selcetion?
I - Inherited variation exists within the population
C - Competition results from an overproduction of offspring
E - Environmental pressures lead to differential reproduction
A - Adaptations which benefit survival are selected for
G - Genotype frequency changes across generations
E - Evolution occurs within the population
ICE AGE
What two types of variation exist?
This variation can manifest as either discontinuous (distinct classes) or continuous (range across a characteristic spectrum)
What are the main mechanisms by which genetic variation between individuals in a species may occur:
Mutations – Changing the genetic composition of gametes (germline mutation) leads to changed characteristics in offspring
Meiosis – Via either crossing over (prophase I) or independent assortment (metaphase I)
Sexual reproduction – The combination of genetic material from two distinct sources creates new gene combinations in offspring
Define gene mutation
A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait
How does meiosis cause genetic variation?
- Crossing Over
Crossing over involves the exchange of segments of DNA between homologous chromosomes during prophase I
The exchange of genetic material occurs between non-sister chromatids at points called chiasmata
As a consequence of this recombination, all four chromatids that comprise the bivalent will be genetically different
Chromatids that consist of a combination of DNA derived from both homologous chromosomes are called recombinants
Offspring with recombinant chromosomes will have unique gene combinations that are not present in either parent
- Independent Assortment
When homologous chromosomes line up in metaphase I, their orientation towards the opposing poles is random
The orientation of each bivalent occurs independently, meaning different combinations of maternal / paternal chromosomes can be inherited when bivalents separate in anaphase I
The total number of combinations that can occur in gametes is 2n – where n = haploid number of chromosomes
Humans have 46 chromosomes (n = 23) and thus can produce 8,388,608 different gametes (223) by random orientation
If crossing over also occurs, the number of different gamete combinations becomes immeasurable
How does sexual reproduction lead to variation?
The fusion of two haploid gametes results in the formation of a diploid zygote
This zygote can then divide by mitosis and differentiate to form a developing embryo
As meiosis results in genetically distinct gametes, random fertilisation by egg and sperm will always generate different zygotes
This means that individual offspring will typically show variation despite shared parentage
How does competition form between species
If left to follow course, a stable population will inevitably outgrow its resource base, leading to competition for survival
When there is an abundance of resources, a population will grow according to its biotic potential (exponential curve)
With more offspring, there are less resources available to other members of the population (environmental resistance)
This will lead to a struggle for survival and an increase in the mortality rate (causing population growth to slow and plateau)
What are adaptations and how may they be classified?
Adaptations are features of organisms that aid their survival by allowing them to be better suited to their environment
These adaptations may be classified in a number of different ways:
-Structural: Physical differences in biological structure (e.g. neck length of a giraffe)
-Behavioural: Differences in patterns of activity (e.g. opossums feigning death when threatened)
-Physiological: Variations in detection and response by vital organs (e.g. homeothermy, colour perception)
-Biochemical: Differences in molecular composition of cells and enzyme functions (e.g. blood groups, lactose tolerance)
-Developmental: Variable changes that occur across the life span of an organism (e.g. patterns of ageing / senescence)
Define and explain adaptive radiation with reference to one example
Adaptive radiation describes the rapid evolutionary diversification of a single ancestral line
It occurs when members of a single species occupy a variety of distinct niches with different environmental conditions
Consequently, members evolve different morphological features (adaptations) in response to the different selection pressures
An example of adaptive radiation can be seen in the variety of beak types seen in the finches of the Galapagos Islands
These finches have specialised beak shapes depending on their primary source of nutrition (e.g. seeds, insects, nuts, nectar)
Define and explain adaptive radiation with reference to one example
Adaptive radiation describes the rapid evolutionary diversification of a single ancestral line
It occurs when members of a single species occupy a variety of distinct niches with different environmental conditions
Consequently, members evolve different morphological features (adaptations) in response to the different selection pressures
An example of adaptive radiation can be seen in the variety of beak types seen in the finches of the Galapagos Islands
These finches have specialised beak shapes depending on their primary source of nutrition (e.g. seeds, insects, nuts, nectar)
Discuss antibiotic resistance in connection to evolution [ 5 marks ]
Antibiotics are chemicals produced by microbes that either kill (bactericidal) or inhibit the growth (bacteriostatic) of bacteria which are prescribed to humans fighting bacterial infections
In a bacterial colony, over many generations, a small proportion of bacteria may develop antibiotic resistance via gene mutation
When treated with antibiotics, the resistant bacteria will survive and reproduce by binary fission (asexual reproduction)
Antibiotic resistant bacteria may also confer resistance to susceptible strains by transferring plasmids via bacterial conjugation
The introduction of antibiotic (selection pressure) has caused the antibiotic resistance gene to become more frequent (evolution)
What is the binomial system of nomenclature and what is its value? [ 5 marks ]
The binomial system of nomenclature is the formal system by which all living species are classified (taxonomy)
-It allows for the identification and comparison of organisms based on recognised characteristics
-It allows all organisms to be named according to a globally recognised scheme
-It can show how closely related organisms are, allowing for the prediction of evolutionary links
-It makes it easier to collect, sort and group information about organisms
How do we name organisms?
Genus with a capital letter first, then species from lower case
Homo sapiens
State and define the three domains of life
Eukarya – eukaryotic organisms that contain a membrane-bound nucleus (includes protist, plants, fungi and animals)
Archaea – prokaryotic cells lacking a nucleus and consist of the extremophiles (e.g. methanogens, thermophiles, etc.)
Eubacteria – prokaryotic cells lacking a nucleus and consist of the common pathogenic forms (e.g. E. coli, S. aureus, etc.)
List the taxa in order
Kingdom
Phylum
Class
Order
Family
Genus
Species
[K]aty [P]erry [C]omes [O]ver [F]or [G]reat [S]ex
Discuss different forms of classification [ 6 marks ]
Artificial classification involves arbitrarily selecting unifying characteristics first and then grouping organisms accordingly
The advantage of artificial classification is that such schemes are easy to develop and relatively stable (unlikely to change)
The disadvantage is that they do not generally show evolutionary relationships and for this reason are not commonly used
For example, if organisms were classified according to the presence of fins then whales would be grouped with fish
If organisms were classified based on the presence of shells then snails would be grouped with turtles and not with squid
Natural classification involves grouping organisms based on similarities first and then identifying shared characteristics
According to a natural classification system, all members of a particular group would have shared a common ancestor
This means that natural classification schemes can be used to predict characteristics shared by species within a group
A disadvantage of such schemes is that they are highly mutable and tend to change as new information is discovered
A third type of classification – phylogenetic classification – is now being used to differentiate organisms based on genetics
Organisms who share a greater level of homology in their DNA or amino acid sequences are expected to be more closely related
Why may organisms be re-classified? [ 3 marks ]
Taxonomists will reclassify groups of species when new evidence arises to compromise the traditional classification scheme
Groups of species may be separated into different genera if new evidence suggests they evolved from different ancestral species
Species originally classified as figworts have been reclassified into different genera based on DNA sequence comparisons
Alternatively, different species may be grouped into a shared taxon if new evidence suggests more recent common ancestry
The Homininae sub-family was created to include gorillas and chimpanzees when it was deduced that they share more common ancestry with humans than with other great apes (e.g. orang-utan)
State the characteristic features of Bryophyta
Bryophyta
Has no vascularisation (i.e. lacks xylem and phloem)
Has no ‘true’ leaves, roots or stems (are anchored by a root-like structure called a rhizoid)
Reproduce by releasing spores from sporangia (reproductive stalks)
Examples include mosses and liverworts
State the characteristic features of Filicinophyta
Filicinophyta
Has vascularisation (i.e xylem and phloem)
Have leaves, roots and stems (leaves are pinnate – consisting of large fronds divided into leaflets)
Reproduce by releasing spores from clusters called sori on the underside of the leaves
Examples include ferns
State the characteristic features of Coniferophyta
Coniferophyta
Has vascularisation
Have leaves, roots and stems (stems are woody and leaves are waxy and needle-like)
Reproduce by non-motile gametes (seeds) which are found in cones
Examples include pine trees and conifers
State the characteristic features of Angiospermophyta
Angiospermophyta
Has vascularisation
Have leaves, roots and stems (individual species may be highly variable in structure)
Reproduce by seeds produced in ovules within flowers (seeds may develop in fruits)
Examples include all flowering plants and grasses
State the characteristic features of Porifera
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
Examples include sea sponges
State the characteristic features of Cnidaria
Cnidaria
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
State the characteristic features of Platyhelmintha
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
State the characteristic features of Annelida
Annelida
Have bilateral symmetry
Have a separate mouth and anus
Body composed of ringed segments with specialisation of segments
Examples include earthworms and leeches
State the characteristic features of Mollusca
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)
State the characteristic features of Arthropoda
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
State the characteristic features of Chordata
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)
State the characteristic features of Fish
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)
State the characteristic features of Amohibian
Amphibian
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)
State the characteristic features of Reptiles
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)
State the characteristic features of 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)
State the characteristic features of Mammals
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)
What is a dichotomous key and how does it work?
A dichotomous key is a method of identification whereby groups of organisms are divided into two categories repeatedly
With each sequential division, more information is revealed about the specific features of a particular organism
When the organism no longer shares its totality of selected characteristics with any organism, it has been identified
Define clade
A clade is a group of organisms that have evolved from a common ancestor
What is a cladogram? and what can be read from it?
Cladograms are tree diagrams that show the most probable sequence of divergence in clades.
Cladograms are tree diagrams where each branch point represents the splitting of two new groups from a common ancestor
Each branch point (node) represents a speciation event by which distinct species are formed via divergent evolution
Cladograms show the probable sequence of divergence and hence demonstrate the likely evolutionary history (phylogeny) of a clade
The fewer the number of nodes between two groups the more closely related they are expected to be
List and explain the key features of a cladogram?
Constructed cladograms all typically share certain key features:
Root – The initial ancestor common to all organisms within the cladogram (incoming line shows it originates from a larger clade)
Nodes – Each node corresponds to a hypothetical common ancestor that speciated to give rise to two (or more) daughter taxa
Outgroup – The most distantly related species in the cladogram which functions as a point of comparison and reference group
Clades – A common ancestor and all of its descendants (i.e. a node and all of its connected branches)
Why may base pairs be used to analyse wether two organisms are related? [ 4 marks ]
All organisms use DNA and RNA as genetic material and the genetic code by which proteins are synthesised is (almost) universal
This shared molecular heritage means that base and amino acid sequences can be compared to ascertain levels of relatedness
Over the course of millions of years, mutations will accumulate within any given segment of DNA
The number of differences between comparable base sequences demonstrates the degree of evolutionary divergence
A greater number of differences between comparable base sequences suggests more time has past since two species diverged
Hence, the more similar the base sequences of two species are, the more closely related the two species are expected to be
In practice how is the analysis of base pairs between organisms done?
When comparing molecular sequences, scientists may use non-coding DNA, gene sequences or amino acid sequences
Non-coding DNA provides the best means of comparison as mutations will occur more readily in these sequences
Gene sequences mutate at a slower rate, as changes to base sequence may potentially affect protein structure and function
Amino acid sequences may also be used for comparison, but will have the slowest rate of change due to codon degeneracy
Amino acid sequences are typically used to compare distantly related species (i.e. different taxa), while DNA or RNA base sequences are often used to compare closely related organisms (e.g. different haplogroups – such as various human ethnic groups)
Discuss the use of base sequences to compare species [ 4 marks ]
Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.
However,
Different genes or proteins may change at different rates (e.g. haemoglobin mutates more rapidly than cytochrome c)
The rate of change for a particular gene may differ between different groups of organisms
Over long periods, earlier changes may be reversed by later changes, potentially confounding the accuracy of predictions
Define and explain convergent evolution
Convergent evolution is the independent evolution of similar features in species with distinct lineages
It may occur when different species occupy the same habitat and are thus subjected to the same selection pressures
The shared conditions cause common adaptations to be selected in different species, resulting in structural similarity
An example of convergent evolution is the development of wings in birds, bats and insects
Define homologous and analogous structures
Traits that are similar because they are derived from common ancestry are termed homologous structures
Traits that are superficially similar but were derived through separate evolutionary pathways are termed analogous structures
State and explain the limitation of using morphological features for classification [ 2 marks ]
Closely related organisms can exhibit very different structural features due to adaptive radiation (e.g. pentadactyl limb)
Distantly related organisms can display very similar structural features due to convergent evolution
Discuss reclassification in reference to the figworts family
Until recently, figworts were the 8th largest family of flowering plants (angiosperms), containing 275 different genera
This was problematic as many of the figwort plants were too dissimilar in structure to function as a meaningful grouping
Taxonomists examined the chloroplast gene in figworts and decided to split the figwort species into five different clades
Now less than half of the species remain in the figwort family – which is now the 36th largest among angiosperms
What are the main mechanisms for change which will reduce biodiversity within a population?
Genetic drift: The change in the composition of a gene pool as a result of a random or chance event
Natural selection: The change in the composition of a gene pool as a result of differentially selective environmental pressures
What causes variation within a gene pool tobe reduced
Variation within a gene pool can be reduced if conditions promote the survival of certain traits and the removal of others
Describe the process of fossilisation
- Death and decay – Soft body parts are decomposed or scavenged, leaving only the hard body remains
- Deposition – The hard remains are rapidly covered with silt and sand, and over time more layers continue to build
- Permineralisation – Pressure from the covering layers of dirt/rock cause the hard organic material to be replaced by minerals
- Erosion / exposure – Movement of earth plates may displace the fossil and return it to the surface for discovery
Domain to species for humans
Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Mammal
Order: Primate
Family: Hominid
Genus: Homo
Species: Sapiens
Domain to species for Ruccola
Domain: Eukarya
Kingdom: Plantea
Phylum: Tracheophyta
Class: Spermatophytes
Order: Brassicales
Family: Brassicaceae
Genus: Eruca
Species: Vesicaria
