BIO EXAM REVISION

a species

is a group of similar organisms that can interbreed in nature and produce vigorous, fertile offspring

subspecies are

different races of the same species, who do not interbreed directly (gene flow can still exist)

extinction

the permanent loss of a species (usually hasn’t been seen for 50 years or more)

a population is a

group of organisms of the same species living in a defined geographic region at the same time.

gene pool:

the genetic makeup of a population; includes the sum of all the alleles for different genes present in a population

gene flow is the

movement of genes and alleles between populations

gene flow can occur through

immigration or emigration or random mating between individuals

Immigration

= individuals move into a population → bring in new alleles

Emigration

= individuals move out of a population → remove alleles.)

gene flow increases the

genetic diversity within a population

when gene flow stops

speciation can occur

variation is important for a

population to survive any sudden change in their environment

variation occurs when

members of a population display different phenotypes (traits)

variation traits can include

physiological, structural, or behavioural

sources of variation are (reg)

• reproduction

• environment

• gene mutation

reproduction source of variation

• sexual reproduction (lots)

• asexual reproduction (little)

• gene mutation variation

• change in DNA base sequence

• introduces new alleles, leading to new genetic variation

• only passed on if mutation occurs in germline cell

• environment variation

acts as a selection pressure on phenotypes

high genetic diversity in a population

• large population size

• random mating by sexual reproduction

• immigration

• mutations resulting in different phenotypes

allele frequencies can measure

• genetic diversity by examining the gene pool of a population and calculating the allele frequency

• allele frequency differences may be due to chance or due to selection by selection pressures

• if a population has a wide range of alleles in their population it means they are genetically diverse

allele frequencies

• how common an allele is in a population is referred to as the allele frequency

does the allele frequency in each population stay the same?

• no the allele frequency in each population will differ

allele frequency differences may be due to

chance or due to selection by selection pressures

if a population has a wide range of alleles in their population it means

they are genetically diverse

hardy weinberg equilibrium allele frequency formula

• p+q=1

  p: represents the frequency of the dominant allele.

• q: represents the frequency of the recessive allele.

hardy weinberg equilibrium genotype frequencies formula

• p² + 2pq + q² = 1

  p: represents the frequency of the dominant allele.G

• q: represents the frequency of the recessive allele.g

• p²: represents the frequency of the homozygous dominant genotype. GG

• 2pq: represents the frequency of the heterozygous genotype.Gg

• q²: represents the frequency of the homozygous recessive genotype.gg

q =

total recessive alleles/total alleles in population

p =

1 - q

genetic drift refers to

• the random changes in allele frequency due to chance events

what populations does genetic drift occur in

• occurs in all populations

what populations does genetic drift have a more pronounced effect on and what can it result in

• it has more of a pronounced effect in small populations and can result in the loss or fixation of an allele

• can result in reduced genetic diversity in small populations

types of genetic drift

bottleneck effect, founder effect

the founder effect occurs when .. and results in a

• a few individuals migrate to create a new population in a different location that is not representative of the original population

• the individuals are genetically different to the original population resulting in a different gene pool

• could occur due to habitat fragmentation (where a population becomes separated)

the founder effect often results in … due to ..

• often low levels of genetic variation due to only a few founding individuals

the bottleneck effect

• the severe reduction of individuals in a population generally due to a catastrophic event (e.g. disease, bushfire, human impact)

the bottleneck effect over time population will increase in numbers but

• the genetic variation stays low as only have the gene pool from surviving individuals

geological timescale

• the oldest fossils are between 3 billion and 3.5 billion years old. these are fossil bacteria, and for most of earth hisstory, life was simple.

• more complex animals appeared in the oceans about 565 million years ago and became much more common about 542 mullion years ago

• this last section in time is the start of a division of geological time called the phanerozoic eon. phanerozoic means “visible life” and is the time in which fossils are abundant

fossil succession

• fossils appear in an order of “fossil succession” from single cellular organisms to structurally complex multicellular organisms.

significance of mass extinctions

• several mass extinctions have occurred throughout earths history

• mass extinctions provide opportunities for other species to thrive and diversify

fossil record

the information derived from fossils. The fossil record is arranged in chronological order and helps us map the history of life on Earth, placing species in the appropriate geologic time frame

fossils

• the remains of an organism or direct evidence of its presence once on the earth

fossil record is incomplete (there are missing species in the evolutionary chain) as

• • most organisms do not get fossilized (e.g. organisms with hard body parts are more likely to fossilize than those with soft parts)

  • or the fossils are too old and there is no DNA (which means we cant determine how the fossil is related to other species)

• most fossils are found in

• sedimentary rock

how are fossils formed in sedimentary rocks

• formed by mineralization

  • body parts are replaced by hard minerals as the surrounding sediments turn into rock

conditions for fossilisation (RUD)

-very rare

• rapid burial (R)

  • covered in sediment (usually under water)

• organism lies undisturbed (U)

  • no predators

  • no earthquakes, etc.

• decomposition is prevented (D)

  • low o2, low temp, etc, to prevent bacterial decomposition

types of fossils

1. body fossil

2. trace fossil

3. index fossil

4. transitional fossils

body fossil

• fossils of the actual organism

• e.g. bones, teeth, and claws

• soft tissues (e.g. tissue, muscle, organs etc) are very rarely fossilized

trace fossil

• not the actual organism

• e.g. burrow, footprints, faeces

index fossil

• a fossil that:

  • had a wide geographic distribution

  • existed for a relatively brief period of time

• fossils that are found in the same rock layer can be estimated to be the same age

  • a form of relative dating

transitional fossils

• intermediate forms of organisms that provide an evolutionary link between species

• e.g. archaeopteryx shows features of reptiles and birds

dating techniques

two methods are used to provide an age (date) for a fossil

1. relative dating

2. absolute (radiometric) dating

relative dating

• the age of one rock is determined by comparing it to another rock

• a fossils relative age is provided

• uses rock layers (formed by stratification) to assign comparative ages to fossils

relative dating is based on. and uses what

the law of fossil succession and uses index fossils

• stratigraphy/stratification

• • the study of the sequence of rock layers (strata) in any one area

  • layers deposit over time

  • older layers are lower

index fossils relative dating

fossils that can be found in the same rock layer as an index fossil can be estimated to be the same age

the principles of correlations allow the

relative age of rocks in different parts of the world to be inferred, based on distinctive index fossils

Occasionally, a strata representing a particular time period may be missing due to

environmental conditions (e.g. flooding, erosion, etc.)

relative dating definition

 a dating technique used to determine the relative age of a fossil by comparing its position to other fossils or rock in surrounding rock strata (layers)

absolute (radiometric) dating

• provides a numerical (absolute) age for a fossil

• the relative amount of parent/daughter is compared

• half life -

• the time taken for half of the parent isotope to decay into its daughter isotope

absolute (radiometric) dating based on

radioactive isotopes and their half lives

isotope carbon-14 decays to .. half life ~.. used to determine..

nitrogen-14,

has a half-life of approximately 5,700 years,

the age of deposits less than 50,000 years old.

isotope uranium-235 decays to .. half life ~.. used to determine..

lead-207,

has a half-life of about 704 million years,

the age of deposits older than 500,000 years.

isotope potassium-40 decays to .. half life ~.. used to determine..

argon-40,

half-life of around 1.3 billion years,

the age of deposits older than 500,000 years.

carbon dating

• date organic (contain C) fossils, less than 50,000 years

half life is approx. 5,700 years

fossilisation

: Organism is buried in sediment or water, gently covering the body.

1. Preservation conditions:

   • Minimal disturbances (scavengers, fungi, bacteria, earthquakes, uplift) to keep the fossil complete or nearly complete.

   • Low oxygen (anaerobic) environment slows decomposition, preserving bones (soft tissues may still decompose).

2. Discovery: Fossils are often uncovered later due to earth movements.

selection of phenotypes

• some individuals are more likely to survive change in their environment due to a particular phenotype

  • at a selective advantage when the selection pressure is applied

  • genetically fit

• Organisms with a more favourable phenotype are at

• an adv as more likely to survive, reproduce and pass on alleles to their offspring

• e.g. antibiotic resistance in bacteria

selection pressures

• predators

• availability of resources (e.g. water, shelter, mating habitat. etc) → due to competition between individuals within a population

• food sources → due to competition

• disease/pathogenic spread

• environmental phenomena (e.g. natural disasters)

• weather conditions/changes (e.g. floods, storms etc)

• abiotic conditions (e.g. temperature, co2 concentration)

natural selection

• proposed by darwin (and wallace) in 1860s

• VIS: Variation in population Selective pressures Inheritance

• variation exists in a population due to mutation

• individuals who have a favourable adaptation/trait will be better suited to the environmental selection pressures

• these individuals will survive and reproduce to pass on their favourable characteristics to their offspring resulting in changes to the allele frequencies

natural selection vs lamarckism

• lamarckism

  • proposed that trait develops in response to the environment

  • use and disuse occurs (if u want it it will happen)

the process of natural selection

• variation exists in individuals within a species that may lead to an advantage if a change in the environment occurs

• variation exists in the population due to mutations

• a selection pressure is present in the environment

• this means some individuals in the population have a survival and reproduction advantage

• individuals that survive pass on the allele to the next generation (through reproduction), resulting in more individuals with the trait

• this results in increased allele frequencies for the trait in the population

selective breeding

• uses the principle of natural selection

• a human (usually a farmer) selects the trait that is desired based on phenotype

• selects two organisms that are showing the trait and breeds them (to increase the chance of offspring having these traits)

• observes the offspring and then selects the offspring with the best version of the desired trait. breeds the offspring

• completes the process many times until the trait is observed in all offspring

• note that the trait might be favourable to humans but not necessarily to the organism as it may reduce genetic diversity in the population

speciation process

• there is variation in the population. there is a lack of reproduction between individuals in the population preventing gene flow (may be due geographic barrier or prezygotic barrier resulting in reproductive isolation)

• different selection pressure act upon each population due to different niches

• over time many different mutations occur in the different populations and they accumulate resulting in phenotypic differences

• once significant differences have accumulated (and the species can no longer interbreed) they are considered to be different species

speciation def

• process by which new species are formed

• a species is a group of very similar organisms that can interbreed in nature and produce vigorous, fertile, offspring.

Pre-zygotic Isolating Mechanisms

Temporal

Ecological

Behavioural

Mechanical
Occurs when physical differences prevent copulation / pollination
Example: Certain breeds of dog are morphologically incapable of mating due to size

Pre-zygotic Isolating Mechanisms Temporal

Occurs when two species mate at different times of year
Example: Frogs live in same pond but breed during different seasons (summer vs spring)

Pre-zygotic Isolating Mechanisms Ecological

Occurs when two species occupy different habitats
Example: Lions and tigers can potentially interbreed, but usually occupy different habitats

Pre-zygotic Isolating Mechanisms Behavioural

Occurs when two species have different courtship behaviours
Example: Certain groups of birds will only respond to species-specific mating calls

Pre-zygotic Isolating Mechanisms Mechanical

Occurs when physical differences prevent copulation / pollination
Example: Certain breeds of dog are morphologically incapable of mating due to size

Post-zygotic Isolating Mechanisms

Hybrid Inviability

Hybrid Infertility

Hybrid Breakdown

Post-zygotic Isolating Mechanisms Hybrid Inviability

Hybrids are produced but fail to develop to reproductive maturity
Example: Certain types of frogs form hybrid tadpoles that die before they can become a frog

Post-zygotic Isolating Mechanisms Hybrid Infertility

Hybrids fail to produce functional gametes (sterility)
Example: Mules are sterile hybrids resulting from mating between a horse and a donkey

Post-zygotic Isolating Mechanisms Hybrid Breakdown

F₁ hybrids are fertile, but F₂ generation fails to develop properly
Example: The offspring of hybrid copepods have less potential for survival or reproduction

Allopatric speciation relies on a

geographical barrier to reproductively isolate groups of organisms in a species, leading to the formation of a new species.

allopatric speciation and steps

speciation due to geographic separation

1. there is variation and gene flow in a population living in a specific geographic area

2. a geographic barrier separates the population (e.g. a river forms or a mountain range forms) and gene flow stops

3. different selection pressures on either side of barrier. different phenotypes are selected for on either side

4. over time many different mutations occur in the different populations, and they accumulate resulting in phenotypic differences

5. the two populations become so different that they become reproductively isolated. if the two populations were brought back together, they could not interbreed. a new species have formed

allopatric speciation - galapagos finches

ancestral finch arrived from mainland south america

finches increased in number and the population many were adapted to the environment

some finches flew to other islands with different selection pressures (food source)

over time, the beak shapes changed and the finches became so different on each island that they became different species

sympatric speciation steps

1. there is variation and gene flow in a population living in a specific geographic area

2. a reproductive barrier prevents some members of the population from reproducing (e.g. mating at different times of the year)

3. over time many different mutations occur in the different populations, and they accumulate resulting in phenotypic differences

4. the two populations become so different that they become reproductively isolated. although the populations live in the same niche, they cannot interbreed. a new species has formed

sympatric speciation howea palms - lord howe island

• one of the worlds best examples of sympatric speciation, when two species from a single ancestor form in the absence of a geographical barrier

• the two species, the kentia or thatch palm (howea forsteriana) and curly palm (h belmoreana), appear to have diverged after they began flowering at different times of year, as a result of differing soil preferences

Sympatric speciation involves the

formation of a new species in populations located in the same geographical location

structural morphology

studies the sizes, shapes and structures of plants, animals and microbes, as well as the interactions between their parts

homologous structures:

• have the same structure but may have a different function

• evidence of different selection pressures

• evidence of a common ancestor (divergent evolution)

analogous structures:

• a different structure but the same function

• due to similar selection pressures

• no common ancestor (evidence of convergent evolution)

vestigial structures

• a vestigial structure is a feature that a species inherited from an ancestor but that is now less elaborate and functional than in the common ancestor

• due to a lack of selection pressure

vestigial structures example

• e.g. whales still have a pelvic bone, however it is much smaller in size due to a lack of selection pressure (e.g. live in water vs live on land)

• e.g. flightless birds like emus/ostriches have reduced wing sizes, due to lack of selection pressure (e.g. food sources on the ground)

molecular homology

• study of the similarity or difference or molecular information (nucleic acid or amino acid sequence)

• can determine evolutionary relationships based on how similar/different the sequences are

• often used to construct phylogenetic trees

when talking about how related are species are acronym

TAN (time, ancestor mutations)

very closely related →

less mutations as shorter time of divergence

molecular homology

• study of the similarity or difference of molecular information (nucleic acid or amino acid sequence)

nucleic acids can be analysed and compared for differences

• includes nuclear DNA, mRNA, rRNA, mitochondrial DNA

• chloroplast DNA