Evolution

Evolution

Formation of new species from pre-existing species over time, as a result of changes to gene pools from gen to gen.

Change of characteristics of species over time due to changes in allele frequency.

Evolution- process

There is variation in a pop. Many offspring r produced. Change in environmental conditions/ selection pressure. There is comp for resources therefore a struggle for survival. Those best adapted/ the fittest survive to breed. Those that survive pass on their beneficial alleles to the next generation. Process repeats over long periods of time resulting in evolution and change in allele frequencies.

What species is considered a new species through evolution?

For a pop to hv evolved into a separate species it must be genetically + reproductively isolated from the pre-existing species pop.

Gene pool

Collection of genes within an interbreeding population.

Sum of all the alleles at all of the loci within genes of a pop of single species.

Changes in a gene pools

Caused by: genetic drift, natural selection, founder effect

Gene pool changes over time- character of species will also change.

Change can become so great- new species forms- evolution.

Reproductive isolation

Mutations that lead to incompatibility of gametes or diff breeding behaviour.

Genetically isolated

Two pop that don’t exchange genes w each other.

Evolutionary relationships in DNA

DNA found in the nucleus, mitochondria and chloroplasts can be sequenced- show evolutionary relationships between species

More similar sequence= more closely related species r

DNA analysis

DNA is extracted from the nuclei of cells. Extracted DNA is processed, analysed and base sequence is obtained. Base sequence is compared to that of other organisms

MtDNA

Only maternal mtDNA is present in a zygote. No crossing over occurs in mtDNA so base sequence can only change by mutations.

Used for research of the origins of species, genetic drift, and migration events.

Estimation- relies on MOLECULAR CLOCK THEORY- assumes there is a constant rate of mutation over time. Molecular clock calibrated by using fossils + carbon dating.

Why is mtDNA used?

Higher mutation rate than nuclear DNA- not protected by histone proteins.

Not associated/ protected by w Histone proteins

Mutates faster than nuclear DNA

Many copies of mtDNA in every cell

Is smaller- fewer genes

mtDNA analysis is faster

No enzymes to repair DNA mutations

Inherited form mother only

No crossing over

Mutations occur at a constant rate

Allopatric speciation- def

Development of a new species following geographical isolation.

Sympatric speciation- def

Development of a new species w/o any geographical seperation.

Allopatric speciation

Result of geographical isolation. Separation creates 2 pops of same species who r isolated from each other. There is no genetic exchange.

Sufficient selection pressure or genetic drift acting to change gene pools within both pops will cause the pop to diverge + form separate species.

Allopathic speciation- Effect

Since the pops experience different selection pressures their morphological, physical and behavioural features change

When both pops r reintroduced to each other they can no longer breed

Sympatric speciation

A group of organisms could be living in the same place but there must be 2 existing pops within the group and NO GENE FLOW occurring for speciation to occur.

Ecological separation

Behavioural separation

Polyploidy

Ecological seperation

Pop separated cuz they live in diff environments within the same area. Eg soil pH differs greatly in some areas- affects plant growth

Behavioural speciation

Pops separated cuz they have diff behaviours. Eg. Diff in communication, feeding or social behaviour.

Polyploidy

Organism possesses more than 2 complete sets of chromosomes

Morphological species concept

Set of organisms that share similar physical features that distinguish them from other species

Ecological species concept

Pop of individuals living in the same area at the same time

Biological species concept

A grp of organisms which can breed together to produce fertile offspring which is reproductively isolated from other species.

Why isn’t it always possible to know if 2 organisms belong to the same species

Organisms r dead

Time/ facilities not available to attempt to interbreed them.

May not breed in captivity

Organism may only be able to reproduce asexually.

Organisms might be immature + not able to breed yet

Reasons for inability to breed

Individuals not recognising each other as a potential mate.

Physically unable to mate

Incompatibility of pollen + stigma in plants

Inability of female and male gametes to fuse together

Viable but sterile offspring

Failure of cell division in zygote

Non-viable offspring