D4.1 Natural selection (yr 6) Flashcards
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Overview for the process of natural selection
- Overpopulation of offspring
- Variation in the population due to meiosis, sexual repro and mutations
- Struggle for survival = differential survival where those who best fit the environment tend to survive better
- Reproduction where those who survive pass on their genes to the next gen
3 main sources of variation in a species
Mutation creates new alleles
Sexual repro creates new combinations of alleles
Meiosis - random orientaiton and crossing over for genetic variation
How does genetic variation lead to success?
In a species where there is variation, a change in the enviroment will not elimante all members of the population
Define carrying capacity
The maximum number of individual that an enviroment can provide for. Examples of limiting factors are food, water etc
Define abiotic factors
A selection pressure that is not living etc temp, humidity, light, pH
define density-independent factors
factors that affect the population no matter how big or small a population is, and how dense or sparse the population is.
e.g. oxygen, co2 conc
Example of a species being affected by density-independent factors
Magnellanic penguins are adapted to surviving in the snow and cold, the chicks are covered in down feathersr that allow them tomaintain a healthy body temperature by trapping warm air near their bodies. When snow lands on them they can shake it off and keep dry and warm.
However they are not adapted fo rrain where rain causes the down feathers to stick to the chick’s bodies and the thermal insulation effect is lost = die of hypothermia.
Global climate change causes higher temperatures = rain more frequently = decrease in Magellanic penguin population
Define density-dependent factors
A selection pressure that affects a population more when populaion numbers are higher.
Etc diseases
Describe the concept of fitness
Organisms with high fitness (those which possess characteristics that work well in their environment) have a higher change for survival than those with low fitness (charactersitics that are poorly suited to the environment).
Natural selectiion ends to eliminate those who have low fitness = those who have high fitness have a higher SURVIVAL VALUE and REPRODUCTIVE POTENTIAL
Define survival value and reproductive potential
Survival value: those that have adaptations which are good triats have a higher survival value
Repro potential: The maximum no. of offspring an organism can produce in the absence of offspring mortaility. e.g. if 200 eggs all successfully hatch and grow then repro potential has been fully reached.
to increase repro potential, organisms such as fish produce hundreds of eggs per generation
difference btwn heritable traits and aquired characteristics
heritable traits: the trait is encoded in the organism’s DNA and is passed on to the next generation
aquired characteristic: only affects the organism itself and is not passed on to the next generation, not encoded into DNA
E.g. flamingos are not pink because of pigments generated by DNA but by ingesting plankton which makes them pink
define sexual selection + 1 example
A selection pressure where the reproductive success of an indiviaul results in more offspring compared to others in the population who do not have as much success in finding a mate, driving evolution.
e.g. in birds, exceptionally brightly coloured or shiny feathers can be a way of showing potential mates that they are in good health. This is as the long exaggerated dtail fathers make it difficult for the bird to fly = the bird is clearly healthy to be able to overcome difficulties in flight to escape predators
Males are brightly coloured to attract females and females have dark and dull colours that blend in to avoid predators = SEXUAL DIMORPHISM
The competition btwn males for access to females is called INTRASEXUAL COMPETITION
Describe + interpret Endlers experiment
An investigation into the evolution of colouration of guppies in the presence/absence of predators where:
predation leads to high fitness to include more cryptic colours to blend into the background, where allele frequencies for colourful alleles decreases over time
Sexual selection (w. absence of predation) leads to high fitness to include more colourful colours to attract more females, and allele frequencies for colourful alleles increases over time
In the experiment itself coarse and fine gravel were used, so fish with predators evolved to have a pattern of spots to best camoflague whereas the fish w no predators evolved a pattern of spots to make them most visible
The experiment was also repeated in a stream, where guppies with dangerous predators remained full coloured whereas guppies w/o predators evolved to be colourful for sexual selection
Define the gene pool
A gene pool consists of all the genes and their different alleles present in a population
Describe the human leucocyte antigen complex
A set of genes found on chromosome 6 that is involved in producing proteins that produce molecule to allow the cell to be recognised by the immune system. If not recognised, antigens are released.
This is why organ transplants are usually incompactible, as if the 2 human leucocyte antigen complexes are sufficiently different, the organ will be rejected
What are polymorphisms?
A gene/group of genes that shows multiple variations
What is neo-Darwinism?
a more modern modified version of Darwinisim, which incorporates concepts of genetics to explain changes in population.
there is less focus on phenotypic traits and a large focus on genetic variation to drive evolution
Differences btwn directional, stabilizing and disruptive selection + describe their graphs (before and after)
Directional: one phenotype is favoured over another by natural selection (selection AWAY from the extreme)
graph = shift from one extreme to the other
Stabalizing: one phenotype is favoured over two extreme phenotypes (selection AWAY from TWO extremes)
graph = nice shape curve becomes more bell-shaped in the centre
Disruptive: two extreme phenotypes faoured by natural selection rather than one intermediate phenotype (2 opposing extreme varities instead of 1)
Graph = from nice shape to m shape
Describe the Hardy-Weinberg eqn
p+q=1 and
p^2 + 2pq + q^2 = 1
where
p = frequency of dominant allele
q = frequency of recessive allele
p^2 = frequency of homozygous dominant
q^2 = frequency of homozygous recessive
pq = frequency of heterozygous
Assumptions for Hardy-Weinberg equation to be true
- A population needs to have reached a stable equilibrium in which the allele frequency does not change over time.
- organisms studies must be diploid
- population being studied must be large
- population must reproduce sexually
- Gene being studies CANNOT BE SEX-LINKED
- mating must be random
- no migration in or out of population
- none of the allels being studied can reduce the chances of survival (e.g. cause a deadly genetic disease)
Differences btwn natural and artificial selection
Natural:
- Results from mutations in genes
- selection brought by changes in environmental conditions
- Relatively slower process
- may be advantegeous/harmful to man (????)
Artificial:
- Results from manipulation by humans
- humans select organisms with desired traits to reproduce
- Relatively faster process
- Advantegeous to Man (???)
describe how antibiotic resistance in bacteria happens
- Somebody with a bacterial infection (e.g. tuberculosis) gets antibiotics and gets better, as the vast majority of bacteria are destroyed
- However thanks to a pre-existent variation in its genetic makeup one/a few bacterium is resistant
- this bacterium multiplies, and when the same antiobiotic is used there is no effect.
- the bacterium also multiplies very fast as there is little competition for space and food so the mutant strain can flourish
- antibiotic resistant bacteria are created
