A4. 1 Flashcards
Evolution and Speciation
1
Q
Genetic Basis for Evolution
Define Evolution
A
‘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)
2
Q
Genetic Basis for Evolution
Lamarck’s Theory of Evolution
A
- 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.
3
Q
Genetic Basis for Evolution
Charle’s Darwin’s Theoary of Natural Selection
A
- 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.
4
Q
Genetic Basis for Evolution
Falsification of Theories
A
- 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.
5
Q
Genetic Basis for Evolution
Molecular Evidence for Evolution
A
- 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
6
Q
Genetic Basis for Evolution
Patterns in DNA comparisons
A
- 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.
7
Q
Genetic Basis for Evolution
Hox Genes and Evolution
A
- 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.
8
Q
Genetic Basis for Evolution
What are phylogentic trees?
A
- 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/
9
Q
Evidence for Evolution
What is Selective Breeding?
A
- choosing males and females with the most desirable characteristics (in terms of agricultural purposes) and breeding them together
10
Q
Evidence for Evolution
What is Artificial Selection?
A
- 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.
11
Q
Evidence for Evolution
What are Homologous Structures?
A
- 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
12
Q
Evidence for Evolution
What are Pentadactyl Limbs?
A
- 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.
13
Q
Evidence for Evolution
What are Analogous Structures?
A
- 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
14
Q
Evidence for Evolution
Impacts of Selective Breeding
A
- 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
15
Q
Evidence for Evolution
Functional Variations of Pentadactyl Limbs in Mammals.
A
- 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.
16
Q
Evidence for Evolution
Homologous Structures and Divergent Evolution.
A
- 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.
17
Q
Evidence for Evolution
Analogous Structures and Convergent evolution
A
- 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.
18
Q
Evidence for Evolution
The evolution of Central Nervous Systems
A
- 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.
19
Q
Speciation and Reproductive Isolation
What is Speciation?
A
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.
20
Q
Speciation and Reproductive Isolation
What is Reproductive Isloation?
A
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.
21
Q
Speciation and Reproductive Isolation
What is Geographical Isloation?
A
- 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.
22
Q
Speciation and Reproductive Isloation
What is Sympatric Speciation
A
- 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.
23
Q
Speciation and Reproductive Isolation
What is Allopatric Speciation?
A
- The barrier to reproduction is a physical geographic barrier that leads lack of contact and development of distinct habits.
24
Q
Speciation and Reproductive Isloation
What is Behavioural Seperation?
A
- 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.
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# 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.
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# 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)
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# Speciation and Reproductive Isolation
Two things required for Speciation
1. Reproductive Isolation:
- causing no gene flow between the organisms. Can be either geographic (allopatric speciation), but also behavioural/ temporal. (sympatric speciation)
2. Differential Selection:
- different selective pressures on the two groups ---> change and develop different from one another.
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# 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.
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# 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.
30
# 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.
31
# 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.
32
# 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.
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# 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.
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# 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.
35
# 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)
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# 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.
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# 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.
