Topic 3.2 Natural Selection Flashcards
Darwins Theory of Evolution
-Living organisms produce more offspring than those that survive
-All organisms show variation due to mutation
-If conditions change then some organisms will be better suited to the new environment that others
-There will be competition, those which are better suited will survive (survival of the fittest)
-Those which survive will reproduce and pass on the allele to the next generation
-All the offspring will have the allele for the beneficial characteristic, there is an increase in the allele frequency
-Over time a new species may arise or evolve which is different to the original species.
Niche
The role of an organism in an ecosystem based on the adaptations that have.
Anatomical adaptations
Involve the form and structure of an organism (eg. the thick layer of blubber in seals).
Physiological adaptations
Involve the way the body of the organism works and includes differences in biochemical pathways or enzymes (eg. diving mammals can stay underwater for longer that non-diving mammals without drowning, venom production).
Behavioural adaptations
Involves changes to programmed or instinctive behaviour making organisms better adapted for survival (eg. many insects and reptiles orientate themselves to get maximum sunlight on their bodies when the air temperature is low, hibernation).
Social behaviour
Social behaviour such as hunting as a team or huddling together for warmth can improve survival chances. Migrating to avoid harsh conditions and using tools are other examples of behavioural adaptations.
Selection pressures
-A change in the environment means the selection pressure has changed
-The changes in selection pressure result in changes or evolution within the species.
Directional pressure
-Is shown when there is a change from one dominant phenotype to the other
-This is in response to a change in the environment- one phenotype is elected for over all the others
-Speciation: eventually, over many generations a new species may arise.
Natural selection in moths
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Antibiotic resistance
-Pathogens also show mutations adaptions and natural selection
-As a result they can becomes resistant to medicines especially antibiotics
-The antibiotic quickly becomes ineffective
-There is an evolutionary arms race to develop new antibiotics against pathogens
Beating bacteria, Step 1
The Penicillin family of antibiotics affect gram-positive bacteria with their thick peptidoglycan walls, but do not affect other bacteria.
A range antibiotics were developed and for a short time it appeared that bacteria diseases would almost become a thing of the past.
Antibiotics were prescribed freely and everyone came to expect an antibiotic prescription when they went to doctors with an infection.
Bacteria fight back
The presence of an enzyme called penicillinase that splits the penicillin molecule so it no longer works.
People became seriously ill and died from bacterial infections that were no longer effected by penicillin.
Beating bacteria, Step 2
As penicillin resistance spread, scientists produced a new antibiotic called methicillin.
However this didn’t last long.
There are growing numbers of bacteria that are resistant to not just one but many antibiotics.
Factors that contribute to bacteria resistance
-Antibiotics are too widely prescribed
-People do not complete courses of antibiotics
-A lack of basic hygiene in hospitals
-No financial incentive for pharmaceutical companies to develop new antibiotics
How to overcome the problem of bacteria resistance
-Reducing the use of antibiotics
-Better education so people understand they don’t always need antibiotics
-DNA sequencing will help identify bacteria and find ways to target them
-Development of new antibiotics
Bactericidal
Antibiotics are bactericidal meaning they kill the bacteria.
Bacteriostatic
Meaning they slow the growth of bacteria (antibiotics can also be bacteriostatic).
They interfere with the process the bacteria need to multiply, such as protein production, DNA replication or metabolism.
Example of bactericidal antibiotics
Penicillin is an example of a bactericidal antibiotics, which targets the peptidoglycan layer in the cell wall leading to cell death.
Antibiotics spectrum
Antibiotics can be narrow spectrum, affecting only one or two species of bacteria, or a broad spectrum, affecting many different species of bacteria in the body.
The important points to prevent resistance
-Antibiotics do not need to be taken for colds and flu as these usually get better on their own
-It is important to take the antibiotic exactly as instructed and complete the course
-Antibiotics are prescribed for a particular infection, they should not be taken for a different illness.
Speciation
Speciation is the evolution of two different species from an existing one.
(The formation of a new species).
Speciation in general
- A population becomes separated into two groups that are reproductively isolated so that there is no gene flow between the groups
- The two groups’ environment are different, so natural selection favours different characteristics
- The allele frequencies in two groups will change in different ways
- Eventually the two populations will be unable to interbreed, so will be different species.
How does speciation occur?
Speciation occurs when gene flow has effectively stopped between populations where it has previously existed. This requires two populations of the same species to become reproductively isolated.
Isolation leading to speciation
Isolation can be geographical, leading ti allopatric speciation, or due to changes in reproduction mechanism, leading to sympatric speciation.
Geographic isolation
A physical barrier such as a river or a mountain range separates individuals from an original population.
When a species evolved in geographical isolation and is formed in only one place is said to be endemic.
Ecological isolation
Two population inhabit the same region, but develop preferences for different parts of the habitat.
Seasonal isolation (Or temporal isolation)
The timing of flowering or sexual receptiveness in some parts of a population drifts away from the norm of the group. This can eventually lead to the two groups reproducing several months apart.
Behavioural isolation
Changes occur in the courtship ritual, display or mating pattern so that some animals do not recognise others as being potential mates. This might be due to a mutation that changes the colour or pattern of markings.
Mechanical isolation
A mutation occurs that changes the genitalia of animals, making it physically possible for them to mate successfully with only some members of the group, or it changes the relationship between the stigma in flowers, making pollination between some individuals unsuccessful.
Reproductive isolation
Reproductive isolation is the key factor in speciation.
Allopatric speciation
Allopatric speciation takes place when populations are physically or geographically separated in some way.
The physical isolation of populations occur as a result of natural changes (eg. as islands form, as ice floes melt, rivers change and lakes dry up).
Sympatric speciation
Sympatric speciation takes place between populations of a species living in the same place that become reproductively isolated by mechanical, behavioural or seasonal changes (a non-physical barrier eg. a mutation). Gene flow continues to some extent as speciation takes place.
Cichlid speciation
Molecular phylogeny suggests that the great majority of the cichlid fish evolved much more recently than the lakes were formed.
The fish in the lake are more closely related to the other species of fish endemic in their own lake after they have become separated from each other.
