A4. 1 Flashcards
Evolution and Speciation
Genetic Basis for Evolution
Define Evolution
‘Change in the heritable characteristics of a population’. (‘Change in allele frequencies in a population over time’)
- heritable traits (rooted in DNA)
- populations (not individuals/ whole species)
Genetic Basis for Evolution
Lamarck’s Theory of Evolution
- Based on the idea that we actually inherent characteristics that adults accquire over their lifespan.
- He propsed that based on environmental stressors, organisms use different body parts and develop adaptations to help them survive —-> which (adaptations) are then passed onto their offspring.
- We now know that: offspring inherit DNA + changes during lifespan cannot be passed to their offspring.
Genetic Basis for Evolution
Charle’s Darwin’s Theoary of Natural Selection
- Recognized that only traits that can be passed to offspring are those that are heritable.
- Which leads to different traits naturally exisitng in a popualtion. (variation of genetics)
- In that environment, some variations (adaptions) aid survival and organisms that survive longer —-> more opportunities to reproduce.
- Since the adaptation is heritable/ genetic, they pass the adaptation to offspring.
- Over many generations, increased frequency of the adaptation.
Change in heritable trait = EVOLUTION.
Genetic Basis for Evolution
Falsification of Theories
- If a theory is falsified, it is discounted.
- If many lines of evidence fail to falsify evidence it then gives strong support for theory.
- Instead of seeking proof, seeking lack of falsification.
Genetic Basis for Evolution
Molecular Evidence for Evolution
- Changes in genes whenever evolution occurs.
- Changes will happen in the base sequence of DNA/RNA and in the ammino acid secquence.
RNA: - Same concept but using MRNA.
- useful for viral evolution that only have DNA.
DNA: - Base Sequences
- provides more informationan/ all diferences detected
- good for closely related species
- codes proteins
Protein - comapre aminno acid sequences of a shared protein.
- much easier to sequence with technology and obtain
- less differences/ less data
- It’s a indirect way (as DNA codes for protiens) to study DNA
Genetic Basis for Evolution
Patterns in DNA comparisons
- More closely the related two species are (based on similar physical traits), the fewer differences in their DNA.
- High level of DNA similarity between species: supports the idea of a common ancestory with evolution occuring by small changes to DNA over long periods of time.
Genetic Basis for Evolution
Hox Genes and Evolution
- Related genes (gene family): an example is the Hox gene family.
- These genes play a role –> determining the body plan of organisms during development.
- Placement of genes —> body to develop in correct sequences/ pattern.
- Level of simarlity —> hard to explain without reference to common ancestory/ evolution.
Genetic Basis for Evolution
What are phylogentic trees?
- Visual diagram showing which organisms are most related.
- Branches and organisms on a closer branch have more gentic similarity.
- Often just comparing similarly for a single common gene among organisms.
https://plato.stanford.edu/entries/phylogenetic-inference/
Evidence for Evolution
What is Selective Breeding?
- choosing males and females with the most desirable characteristics (in terms of agricultural purposes) and breeding them together
Evidence for Evolution
What is Artificial Selection?
- The RESULT of selective breeding
- Outcome after many geenrations of selective breeding organsism now have combinations of traits, not previously seen.
- Change in heritable material of organsisms –> evolution has occured. However, as it is human choice rather than environment/ survial, it is ARTIFICAL selection, rather than natural.
Evidence for Evolution
What are Homologous Structures?
- Share a similar internal structure despite used potentially for different purposes.
- Inherited from a common anncestor but have evolved in diverse ways –> due to being adapted for different functions.
- Divergent evolution
Evidence for Evolution
What are Pentadactyl Limbs?
- An example of a homologous structure
- Refers to the presence of five digits (fingers/ toes), but also generally to a front/ hind leg/arm.
- Made up on the same sets of bones across all organisms.
- Some do not have all five digits anymore, but any limb with the some overall bone structure = pentadactyl limb.
Evidence for Evolution
What are Analogous Structures?
- Body parts that carry out a similar function in each organisms, but are structurally very different. (Bird, Butterfly, Bat.)
- Internal arrangement is unqiue but still faciliates the same function.
- Lack of common ancestory
- Seperately evolved (CONVERGENT evolution —> exist in similar environments developing similar adaptations to suit environment)
- Lack of interal similarity
Evidence for Evolution
Impacts of Selective Breeding
- Modern corn which originated from a teostine plant with very small hard kernals. Selected of larger kernals and protective leaves gave rise to the corn we eat now.
- All modern dog breeds originate from the grey wolf and selective or different traits for different preferences has given rise to so many breeds.
- Cannabis has been breeded for high THCcontent causing the average THC content to have quadrupled in 23 year
Evidence for Evolution
Functional Variations of Pentadactyl Limbs in Mammals.
- Humans, Cats, Whales, Bats.
- The functional use of these limbs varies significantly.
- However, common structure can be seen in the pentadactyl limbs across most animals including insents, birds and reptiles.
- The structural similarities are most ‘pronounced’ when studying mammals who have similar BONE arragangements.
Evidence for Evolution
Homologous Structures and Divergent Evolution.
- Homologous structures are evidence of a common ancestor.
- How recent the ancestor is can vary
- The structural similarity resembles how it was in the shared ancesotor
- Due to different environments and niches, the species have altered the structure’s use to best meet their needs.
Evidence for Evolution
Analogous Structures and Convergent evolution
- Analogous structures have no structural similarity, but have similar functions.
- Analogous structures are not based on shared ancestory.
- Analogous structures evolve because different species living in the same or similar habitats experience similar selection pressure.
- Analogous structures are evidence for Convergent Evolution.
Evidence for Evolution
The evolution of Central Nervous Systems
- Annelids (earthworms) and arthropods (insects) have a nerve cord and enlarged neural section at one end.
- All vertebrates have a spinal cord and brain.
- When compared THROUGH the nerve cord of these INVERTEBRATES and brain and spinal cord of these three are not seen in more closely related organisms –> not considered to be analogous —> not linked to a shared ancestor of all of them.
Speciation and Reproductive Isolation
What is Speciation?
The formation of a new species by the splitting of an existing spcies.
- Two populations of a species becomes seperated, thus they can not INTERBREED, they will evolve in different ways.
- The characteristics of the two populations will gradually diverge.
- If the two populations then merged and had the chance of interbreeding, but did not —> evolved into seperate species.
Speciation and Reproductive Isolation
What is Reproductive Isloation?
When two populations are no longer able to successfully interbreed with one another and therefore prevent any gene flow or exchange of genetic material between the two groups.
- A requirement for speciation to occur.
- Reasons for inability to produce viable offspring can range, geographic barriers, to mating behaviours not alinging, to anatomical incompatibilty.
Speciation and Reproductive Isolation
What is Geographical Isloation?
- Most common cause of reproductive isloation.
- Gaps in species, which leads to seperate populations, is due to the physical barriers that are difficult to cross (mountain range, lakes etc)
- Prevents males and females to make contact
- Can be natural/ man made
- Mating is never able to even be attempted
- Geographical seperation is usually associated with differences in selection pressure, which is also required for speciation.
Speciation and Reproductive Isloation
What is Sympatric Speciation
- When speciation occurs without a physical barrier having even played a role.
- A new species arises from an existing species living in the exact same area.
- Reproductive isloation is NOT related to PREVENTED contact, but rather mating not occurring DESPITE CONTACT.
- Two groups ‘choose’ not to mate due to incompatible mating times/ rituals.
Speciation and Reproductive Isolation
What is Allopatric Speciation?
- The barrier to reproduction is a physical geographic barrier that leads lack of contact and development of distinct habits.
Speciation and Reproductive Isloation
What is Behavioural Seperation?
- A cause of sympatric speciation (new species arising in the same habitat)
- Occurs when the mate attracting actions of one group are different to the mate attracting behaviours of another.
- Common in organisms that have more elaborate courtship rituals.
- Can also be an adaptation to prevent unsuccessful mating attempts between organisms with different chromosomes.
Speciation and Reproductive Isloation
What is Temporal Separation?
- Another cause of Sympatric Speciation is temporal separation/ isloation.
- Organisms have different mating times
- Plants/ animals have mating seasons and can only produce gamates during those times.
- Could be due to the time of day
- Can be an effective strategy to minimise unsuccessful mating attempts.
Speciation and Reproductive Isolation
What is Adaptive Radiation?
‘A pattern of diversification in which species that have evolved from a common ancestor to occupy a range of ecological roles.’
- Allopathic speciation can lead to Adaptive radiaiton.
- Occurrs when many similar but distinct species evolve relatively rapidly from a single species or form a small number of species. —-> occurrs when groups move into different niches —> natural selection —> evolve adaptations for that niche.
- Different groups become different species.
- Process which allows closely related species to coexist without compeition (by evolving to different niches)
Speciation and Reproductive Isolation
Two things required for Speciation
- Reproductive Isolation:
- causing no gene flow between the organisms. Can be either geographic (allopatric speciation), but also behavioural/ temporal. (sympatric speciation) - Differential Selection:
- different selective pressures on the two groups —> change and develop different from one another.
Speciation and Extinction
Impact of Speciation and Extinction
- Speciation: the only way new species are added.
- Extinction: the process in which species no longer exist.
When speciation is higher than extinction biodiversity increases.
Speciation and Reproductive Isolation
Darwin’s Finches and Adaptive Radiation
- Example of Adaptive Radiation
- 14 different finches evolving from a common ancestor
- Birds migrated to the islands then adapted to the different avilable food sources –> different beak shapes.
- Can now co-exist and use different food sources to survive.
Barriers to Hybirdisation and Abrupt Speciation
What is Hybridisation?
(a process) –> the fertilisation of gamates (sex cells) from one species by the gametes of another species.
- The formation of unsuccessful offspring, who either cannot survive or cannot reproduce themsleves.
Barriers to Hybridisation and Abrupt Speciation
What are interspecific hybrids?
A hybrid is the result of fertilisation between two different species.
- usually formed artificially by merging of gamates
- hybrids are not fertile, unable to produce offspring –> usually due to incompatible number of chromosomes or incompatible gene placements on their chromosomes.
Barriers to Hybridisation and Abrupt Speciation
What is meant by the term ‘polyploidy’?
- A polyploid organisms has more than two sets of homologous chromosomes.
- Polyploidy is a consequence of the duplication of chromosomes in a cell without subsequent cell division, so is it whole-genome duplication.
- This is result of an error in meiosis forming the sex cells, or it can occur as a result of hybirdisation.
- For animals: polyploidy is generally not compatible with life.
- For plants: can survive with three of more sets of chromosomes.
Barriers to Hybridisation and Abrupt Speciation
What is Autotetraploidy?
- The formation of a polypoid organism from memebers of the same species.
- If a whole genome duplication happens in a diploid cell, the result is four sets of homologous chromosomes, so the CELL IS TETRAPLOID.
- And because all the sets of chromosomes come from the same organism, it is called an AUTOTETRAPLOID.
- That autotetraploid organism can produce diploid games so can produce more tetraploid offspring.
- They can reproduce with a diploid plant, but offspring would be infertile.
Barriers to Hybridisation and Abrupt Speciation
What is Allotetrapoloidy?
- If any cell in the sterile interspecific hybrid duplicates chromosomes but then does NOT divide the cell will have four sets of chromosomes –> It is an allotetraploid because the four sets of chromosomes are from two different species.
- It is likely that allotetraploid cells will be able to divide by meiosis —> because they’re two sets of homologous chromosomes of each type —> reliably form pairs.
- Can interbreed with other allotetraploids, but not with either of the diploid parent species.
- Another way that tetraploids form — combining of gamates from two different diploid species (parents) (AA + BB) —> results in hybrid that is sterile, due to not having homologous (AB) chromosomes. If it goes through genome duplication however, (polyploidy process –>AABB) can end up at a tetraploid with homologous chromosomes and sucessfully undergo meiosis and reproduce with other hybrids to create more tetraploids.
Barriers to Hybridization and Abrupt Speciation
What is Abrupt Speciation?
- When a new species is formed from tetraploidy (polyploidy in which a single cell has four sets of chromosomes), the formation of a new species can occur within a couple of generations.
- Known as abrupt speciation due to it happening within so few generations. (typically the process is very slow over many generations, due to the process of reproductive isloation—>natural selection)
Barriers to Hybridization and Abrupt Speciation
Purpose of Barriers to Hybridization
- Most hybrids that form don’t make it do adulthood.
- Many arrest is early embryonic development.
- Those that make it, produce unhealthy offsrping.
- Bad outcome for both species to exert energy on mating to not produce effective offspring.
- Productive barriers prevent two species from even attempting to mate: beneficial for both species.
Barriers to Hybridization and Abrupt Speciation
Examples of Barrier to Hybridization
- To prevent production of infertile hybrids that may have expended energy to produce, species have developed specific courtship rituals that help them identity genetically comaptible offspring.
- In animals: mating attraction/ behaviours
- In plants: temporal isloation strategies or isloating mechanisms, such as behavioural/ geographical.
