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Topic 7 - ID - Coggle Diagram
Topic 7 - ID
Inheritance
Monohybrid
E.g Cystic fibrosis is caused by a recessive allele. If two carriers reproduce the probability of a child with cystic fibrosis is 25%.
Parental genotypes = Ff x Ff
Probability of offspring:
50% - Ff
25% - FF
25% - ff
Chi Squared & Inheritance
Cystic fibrosis is caused by a recessive allele.
Parental genotypes = Ff x Ff
Probability of offspring:
25% - FF
50% - Ff
25% - ff
Chi squared is the statistic to investigate differences between frequencies.
It can be used to determine whether there is a significant difference between the frequency you expect and the frequency you observe.
The Chi Squared test
NULL HYPOTHESIS: There is no significant difference between the expected and observed.
ALTERNATE HYPOTHESIS: There is significant difference between observed and expected.
2 possible results so Degrees of freedom = 1
Chi squared = 3.176 is less than the critical value of 3.841 at p=0.05
This means that there is more than 5% probability that the results are due to chance.
The null hypothesis can be accepted.
There is no significant difference between the observed and expected results.
Codominant
E.g Cows can be red, white or roan in colour. Red and white are both dominant.
Parental genotypes = CwCr x CwCr
Probability of offspring:
50% - CrCw
25% - CrCr
25% - CwCw
Multiple alleles
E.g Parents with blood group AB and blood group 0 reproduce. Ia and Ib are codominant and Io is recessive.
Parental genotypes = IaIb x IoIo
Probability of offspring:
IbIo - 50%
IaIo - 50%
Sex-linkage
E.g Colour blindness is caused by a recessive allele found only on the X chromosome.
Parental genotypes = XRXr x XrY
Probability of offspring:
XR Xr - 25% - Normal vision
XR XR - 25% - Normal vision
Xr Y - 25% - Colour blind
XR Y - 25% - Normal vision
Epistasis
When one gene influences the expression of another gene.
E.g Labradors coat colour.
Parental Genotypes = Ee Bb x EeBb
Gametes: EB Eb eB eb x EB Eb eB eb
Offspring probability:
EEBB - 6.25% - BLACK
EEBb - 12.5% - BLACK
EeBB - 12.5% - BLACK
EeBb - 25% - BLACK
Eebb - 18.75% - BROWN
eeBB - 6.25% - YELLOW
eeBb - 12.5% - YELLOW
eebb - 6.25% - YELLOW
Dihybrid
E.g cross between a round yellow pea and a wrinkled green pea.
Parental genotype: RRYY x rryy
Gametes: RY x ry
Probability of offspring:
RrYy - 100% - ROUND YELLOW
Crossing Over in Meiosis
Crossing over results in new combinations of alleles in the gametes.
This means the predicted gametes in your punnet square.
Autosomal Linkage
When two genes are located on the same chromosome. (Not X and Y)
This means the alleles for each gene linked on the same chromosome will be inherited together.
This impacts the predicted gametes.
Parental genotypes = RrYy x RrYy
Probability of offspring:
RRYY - 25%
RrYy - 50%
rryy - 25%
However, scientists actually observe different results:
This is only possible because crossing over must have occurred during meiosis to make new combinations of gametes.
Hardy weinberg
Allele Frequencies
The Hardy-Weinberg principle is a mathematical model which can be used to predict the allele frequencies within a population.
Gene Pool - All the alleles of all the genes within a population at one time.
Population - All the individuals of one species in one area at one time.
Allele Frequency - The proportion of an allele within the gene pool.
The Equation
p2 + 2pq + q2 = 1
This equation is used simultaneously with the following equation.
p or q must first be identified to enable the use of equation above:
p + q = 1
P = the frequency of the dominant allele
q = is the frequency of the recessive allele
p2 = The frequency of the homozygous dominant .
2pq = The fequency of the heterozygous genotype
q2 = The frequency of the homozygous recessive genotype
Variation
- Individuals within a population of a species may show a wide range of variation in phenotype.
- This is due to genetic and environmental factprs.
- The primary source of genetic variation is mutation.
- Meiosis and the random fertilisation of gametes also introduces genetic variation.
- Predation, disease and competition for the means of survival results in diffrential survival and reproduction. I.e natural selection.
- Those organisms with phenotypes which provide a selective advantage are likely to produce more offspring and pass on their favourable alleles to the next generation. The effect of this differential reproductive success on the allele frequencies within a gene pool.
SelectionThree types of selection:
- Stabilising
- Directional
- Disruptive
Disruptive selection is when individuals which contain the alleles coding for either extreme trait are more likely to survive and pass on their alleles.As a result, the allele frequency changes and more individuals possess the allele for the extreme trait and the middling trait becomes less frequent.Continued disruptive selection can ultimately lead to speciation.
Speciation
Speciation is the process that results in the creation of new species.
This occurs when one original population of the same species becomes reproductively isolated. This isolation means that there are now two populations of the same species, but they cannot breed together.
This can result in the accumulation of differences in their gene pools to the extent that the two populations would be unable to interbreed to make fertile offspring, and therefore are classed as two different species.
Allopatric speciation
Populations can become separated geographically leading to reproductive isolation.
Within all populations there is genetic variation due to random mutation.
E.g:
A population come become geographically isolated over time by new mountain ranges or new water bodies separating land masses. This separates the original population into two, which are now unable to reproduce due to the geographical barrier.
Both separate populations will continue to accumulate different beneficial mutations over time to help them survive in their environments, which are likely to vary.
Due to accumulation of DNA differences over time the two populations become so genetically different that they would be unable to interbreed to create fertile offspring. They are therefore classed as two different species.
Sympatric speciation
Populations can become reproductively isolated due to differences in their behaviour.
E.g
Random mutation within the population could impact reproductive behaviour, for example it may cause individuals to perform a different courtship ritual or for individuals to be fertile at different times of a year.
Due to this, these individuals will not reproduce together and there will be no gene flow between the two groups within the populations;.
Over time these re-productively isolated populations will accumulated different mutations to extent that their DNA is so different that they cannot interbreed to create fertile offspring.
They are therefore classed as two different species.
Genetic Drift
This is the change in the allele frequency within a population between generations.
There will always be genetic drift from one generation to the next, but continual, substantial genetic drift results in evolution.
The smaller a population is the bigger the impact allele frequency changes have proportionally and this is why evolution often occurs more rapidly in smaller populations.
Populations/ecosystems
Populations Key terms
Populations - Group of organisms of the same species living in the same habitat.
Habitat - Part on an ecosystem in which particular organisms live.
Community - All the populations of different species in the same area at the same time.
Ecosystem - A community and the non-living components of an environment (the biotic and abiotic factors). Ecosystems can range in size from the very small to the very large.
Niche - An organisms role within an ecosystem, including their position in the food web and habitat. Each species occupies their own niche governed by adaptation to both abiotic and biotic conditions.l
Carrying capacity - The maximum population size an ecosystem can support.
Abiotic factors - Non-living conditions of an ecosystem.
Biotic factors - Impact of the interactions between organisms.
Factors affecting Population sizePopulation sizes vary due to a variety of factors:
- Abiotic factors
- Biotic factors
- Interspecific competition
- Intraspecific competition
Abiotic factors
The abiotic factors with an ecosystem can affect the size of the different populations.
These factors can range from temperature, oxygen and carbon dioxide concentration, light intensity, pH and soil conditions.
Plants and animals are adapted to the abiotic factors within their ecosystem.
These adaptations develop through the process of natural selection over many generations.
The less harsh the abiotic factors, such as plenty of water and light, the larger the range of species and the larger the population sizes.
Biotic Factors
Biotic factors and the living components of an ecosystem interacting together, such as interspecific and intraspecific competition and predation also affect population size.
Interspecific competition
When members of different species are in competition for the same resource that is in limited supply.
This could be competition for a habitat, food or water.
The individual that is better adapted to the environment is more likely to succeed in the competition.
Intraspecific competition
When members of the same species are in competition for resources and a mate.
Competition for a mate links to courtship rituals.
Individuals that are fitter will have more energy to perform a more impressive courtship ritual, attract more mates.
Predator Prey RelationshipsThe interaction between predators in a food web is represented by consistent trends.Regardless of the species, the relationship always follows the same pattern:
- The size of the predator and the prey population will both fluctuate.
- Always be more prey than predators.
- the size of the population will always change in the prey and then the predators (lag time)
Sampling
Why do we sample?Sampling is more time efficient, and if implemented correctly more accurate.Samples must accurately represent the population. This is ensured by:
- Random sampling in uniform areas to eliminate bias
- Line transects to examine a change over distance.
- Large number of samples (30+)
Random sampling Methods
Used to estimate population sizes that are distributed evenly:
1 - Lie two tape measures at a right angle to create a gridded area
2 - Use a random number generator to generate two coordinates.
3 - Place the quadrat and collect the data (density/percentage-cover/frequency)
4 - Repeat at least 30 times and calculate a mean
Line transectsUsed to estimate population size when they are unevenly distributed e.g. populations which change over distance.Common examples:
- Sandy/rocky shores
- Path or river
Types of Transect
Belt transect: The quadrat is placed at every position along the tape measure.
Interrupted belt transect: The quadrat is placed at uniform intervals along the tape measure e.g every 5 meters.
Line transect method
E.g - Shoreline
1 - Place the tape measure at a right angle to the shoreline.
2 - Place the quadrat every 5 meters / every position.
3 - Collect the data (density/percentage-cover/local-frequency).
4 - Repeat by placing another 30 transects along the beach at right angles to the shoreline.
Mark-Release-Recapture
Method
The mark-release-recapture method is used to estimate the size of motile animals (moving)
1 - An initial sample of the population is captured.
2 - These individuals are then marked and the number caught is recorded. The mark must be weather resistant.
3 - These marked indivduals are released and are left for a period of time to allow them to randomly disperse through the habitat.
4 - Then a second sample is captured.
5 - The total number caught, and the number of marked is recorded.
6 - The size of the population is then estimated on the principle that the proportion marked in the second sample equals the proportion of marked individuals in the population as a whole.
The more times this is repeated the more reliable it is.
-
EthicsHow you capture and how you mark must cause no permanent harmConsiderations for the mark:
- Non-toxic
- Must not increase predation
- Must not decrease reproductivity
AssumptionsThe estimate may not be accurate due to the method assuming the following:
- Population size is constant (no birth/death and no migration)
- Even redistribution (may all congregate in reality).
Succession
Primary Succession
1 - Mosses and smaller pants can now survive, and they further increase the depth and nutrient content of soil.
2- This pattern continues, and as the abiotic factors continue to be less harsh larger plants can survive and change the environment further.
3 - Each new species may change the environment in such a way that it becomes less suitable for the previous species. Therefore each existing species is outcompeted by a new species colonising.
4 - Changes that organisms produce in their abiotic environment can result in a less hostile environment and increases biodiversity.
5 - The final stage in succession is known as the climax community and this is dominated by trees.
Secondary succession
The succession is disrupted and plants are destroyed.
Succession starts again, but the soil is already created, so it does not start from the bare rock seral stage.
Succession Summary
The species richness and number of organisms increases (biodiversity increases).
As succession occurs, the larger plant species and animals start to colonise area.
Conservation of Habitats
The destruction of habitats, usually due to human activity, results in a loss of food and space for organisms and can lead to extinction.
To conserve habitats Succession is often managed.
By maintaining earlier stages in succession, and preventing a climax community, a greater variety of habitats are conserved and therefore a greater range of species.
HUMAN NEED VS CONSERVATION
There needs to be management of the conflict between human needs and conservation in order to maintain the sustainability of natural resources.
E.g.
Forests can be coppiced to provide timber for fuel and furniture, whilst still allowing the trees to survive.