Genetics, Populations, Evolution & Ecosystems 3.7 Flashcards
Populations in ecosystems (AO1)
Define abiotic factor
A non-living / physical / chemical factor
Populations in ecosystems (AO1)
Examples of abiotic factors
soil pH
temperature
salinity (concentration of salt)
carbon dioxide concentration
humidity
light intensity
Populations in ecosystems (AO1)
Define biotic factor
Living / biological factor
Populations in ecosystems (AO1)
Examples of biotic factors
predator
prey / food
disease
presence of opposite sex
Populations in ecosystems (AO1)
Define population
Groups of organisms of the same species living in the same habitat / ecosystem at the same time;
They have the potential to interbreed;
Populations in ecosystems (AO1)
TRUE OR FALSE
Organisisms of the same species that make up a population have the potential to interbreed
TRUE
They will produce fertile offspring
Populations in ecosystems (AO1)
Define community
All the populations of the different species in the same habitat / ecosystem at the same time
Populations in ecosystems (AO1)
Define ecological niche
The role played by an organism in a
habitat/ecosystem governed by adaptations to biotic/abiotic factors
Populations in ecosystems (AO1)
Explain the advantage of different species occupying different niches (1 mark)
Reduced (interspecific) competition for food/resources
Populations in ecosystems (AO1)
Define carrying capacity
Certain size of population of a species that can be supported by the ecosystem
Populations in ecosystems (AO1)
What can reduce carrying capacity?
Habitat loss;
Reductions in food availability;
Increases in the number of predators;
Disease
Populations in ecosystems (AO1)
An ecosystem supports a certain size of population of a species, called the [1] capacity. There are often numerous habitats within an ecosystem. Within a habitat, a species occupies a [2] governed by an adaption to both [3] and biotic conditions. Populations of different species form a [4].
[1] carrying
[2] niche
[3] abiotic
[4] community;;
Populations in ecosystems (AO1)
Ecosystem definition
The interaction between a community and the abiotic components of the environment
Populations in ecosystems (AO1)
Competition between organisms of the same species is known as _________________ competition
intraspecific
Populations in ecosystems (AO1)
Competition between organisms of different species is known as _________________ competition
interspecific
Populations in ecosystems (AO1)
What term describes populations of different species living in the same habitat?
Community
Populations in ecosystems (AO1)
Describe and explain what typical patterns emerge when plotting the population sizes of predators and their prey over time (3 marks).
As prey populations increase, there is an increased availability of food for the predator population;
This causes a (delayed) increase in predator population;
Due to the increase in predators, the prey population
will decline;
A decline in prey populations leads to a shortage of food for the predators, and over time their population will also decline;
This decline reduces the predation on the prey population, allowing for interbreeding and an increase in the population size
(and repeat)
Populations in ecosystems (AO1)
In northern India, there is a conflict of interests between farmers of livestock (eg cows) and people trying to conserve ibex (a type of wild goat).
When livestock are given extra food, their populations can grow too large and compete with ibex.
Name the type of competition between livestock and ibex.
Interspecific
Populations in ecosystems (AO1)
Random sampling reduces __________
bias
Populations in ecosystems (AO1)
Random coordinates are produced using a ________________________
random number generator
Populations in ecosystems (AO1)
Measurements made within quadrat(s)
Number of individuals;
% cover;
Species richness;
Index of biodiversity;
Populations in ecosystems (AO1)
Why use percentage cover rather than frequency / number of individuals to count algae.
Difficult / too many to count / individual organisms not identifiable / too small to identify/count / grows in clumps;
Populations in ecosystems (AO1)
The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes.
Describe how you could estimate the size of a population of sundews in a small marsh (4 marks).
1. Use a grid;
2. Use random number generator for random coordinates (for quadrats);
3. Large sample of quadarts (10 or more);
4. Calculate mean by adding the total number / frequency in a quadrat and divide by number of quadrats;
5. Valid method of calculating total number of sundews, e.g. mean number of plants per m^2 multiplied by number of m^2 in marsh;
Populations in ecosystems (AO1)
Describe how you would determine the mean percentage cover for beach grass on a sand dune (3 marks).
1. Use random number generator for random coordinates (for quadrats);
2. Large number of quadrats (20 or more);
3. Divide total percentage by number of quadrats;
Populations in ecosystems (AO1)
Outline a method the ecologists could have used to determine the plant species richness at one site (3 marks).
1. Use random number generator for random coordinates (for quadrats);
2. Large number of quadrats (20 or more);
3. Count number of different plant species (in each quadrat)
Reject refs to % cover, or counting individuals
Species richness = all the different species (AS content)
Populations in ecosystems (AO1)
In addition to a quadrat, what piece of equipment do you need to undertake systematic sampling?
Line / belt transect
Populations in ecosystems (AO1)
In systematic sampling, quadrats are placed on a transect at ____________ intervals
regular
Populations in ecosystems (AO1)
What type of analysis can systematic sampling using a line or belt transect allow you to undertake?
The impact of an environmental gradient on a population size.
Populations in ecosystems (AO1)
Lettuce is classified in the same family as dandelions. Dandelions commonly grow on roadside verges and may accidentally be sprayed with salt when salt is added to the road in winter.
Describe how you could use a transect to investigate whether the distribution of dandelions changed with increased distance from the road (4 marks).
- Lay tape / rope at right angle / perpendicular to road;
- Take samples at regular intervals;
- Using a quadrat;
- Count numbers / percentage cover of dandelions;
- Use several transects;
Populations in ecosystems (AO1)
Precautions needed when marking pine martens (during mark, release & recapture) to make sure the estimate of population size is valid (1 marks).
Marking does not affect survival e.g. make visible to predators (of the pine marten);
OR Marking not toxic so does not affect survival;
OR Marking does not rub off so recaptured pine martens are identified;
Populations in ecosystems (AO1)
What are the assumptions made when using the the mark-release-recapture method to make valid estimates of population size?
1. The population size does not change between the two capture times.
* There should be no increase in predation of the marked organism
* There should be no migration
2. The marked organisms have enough time to (randomly) disperse/distribute into the rest of the population
3. The marking should not rub off or be lost
4. Sample population is large enough
Populations in ecosystems (AO1)
Mark, release, recapture equation
You must be able to recall and apply this equation
Populations in ecosystems (AO1)
Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands.
Describe how you could use the mark-release-recapture method to estimate the number of Anolis sagrei on one of these islands (3 marks).
1. Capture sample, mark and release;
2. Method of marking does not make it more visible to predators (i.e. does not affect survivial the lizards);
3. Leave sufficient time for lizards to (randomly) distribute (on island) before collecting a second sample;
4. (Population =) number in first sample × number in second sample divided by number of marked lizards in second sample / number recaptured.
Populations in ecosystems (AO2)
20
Populations in ecosystems (AO2)
The scientists used the mark-release-recapture method to determine the number of pine martens in one area of forest. They captured, marked and released a first sample of 25 pine martens. A week later, they captured a second sample of 35 pine martens from the same area of forest. The scientists calculated that there were 125 pine martens in that area of forest.
Using the information provided, calculate how many pine martens in the second sample were marked.
7 pine martens
Populations in ecosystems (AO2)
Blue tits are small birds that live in woods. An ecologist estimated the size of the blue tit population visiting gardens near a wood in November.
- She trapped 28 blue tits. She marked all of these birds with small metal rings on their legs.
- Two weeks later, she trapped another sample of blue tits. Of these birds, 18 were marked and 20 were not marked.
Use the data to estimate the size of the blue tit population.
59
Populations in ecosystems (AO2)
Describe and explain two precautions required to estimate a valid population size for stream tree frogs (2 marks).
1. Marking does not affect survival e.g. make visible to predators;
OR Marking not toxic so does not affect survival;
OR Marking does not rub off so recaptured stream tree frogs are identified;
2. Time delay after release / before recapture so stream tree frogs are spread back into the population;
Succession (AO1)
Hostile environments such as rock and sand are colonised by ______________
pioneer species
Succession (AO1)
Pioneer species example
Lichen
Succession (AO1)
TRUE or FALSE:
Lichen are microorganisms
TRUE
Lichen are a symbiotic association between a fungus and algae and/or cyanobacteria
Succession (AO1)
Characteristics of pioneer species
Photosynthesise;
Fix nitrogen;
Asexual reproduction;
Tolerance to hostile environments;
Succession (AO1)
At each stage in [1], certain species may be recognised which change the [2] so that it becomes more suitable for other species with different adaptations. The new [3] may change the environment in such a way that it becomes less suitable for the previous species.
[1] succession
[2] environment
[3] species
Succession (AO1)
Succession occurs in natural ecosystems.
Describe and explain how succession occurs (5 marks).
1. (Colonisation by) pioneer (species);
2. Change in environment / example of change caused by organisms present e.g. adds more humus;
(humus = is the formation of a thin / basic layer of soil)
3. Enables other species to colonise / survive;
4. Increase in biodiversity;
5. Stability increases / less hostile environment;
6. Climax community;
Succession (AO1)
Final stage of primary succession
Climax community
Succession (AO1)
Features of a climax community
1. Same species present (over long time) / stable community (over long time);
2. Abiotic factors (more or less) constant (over time)
3. Populations stable (around carrying capacity)
Succession (AO1)
What happens to the pioneer species as succession progresses to the next stage?
They are outcompeted;
by species better adapted to the less hostile environment;
(This is a form interspecific competition)
Succession (AO1)
The species that are present change during succession. Explain why (2 marks).
- Species / plants / animals change the environment / less hostile (habitat);
e.g. add humus / nutrients etc. - New species / plants that colonise this environment outcompete original species (e.g. pioneer species);
Succession (AO2)
Crabgrass
Succession (AO2)
1. Beach grass is the pioneer (species);
2. Pioneers/named species change the (abiotic) environment/habitat/conditions/factors;
Accept example of change e.g. more humus
3. (So) less hostile for named species OR
(So) more suitable for named species;
4. Conifer/hardwood trees represent climax community;
Succession (AO2)
Explain the advantage to a plant that colonises 50 years after the pioneer species of having a high rate of photosynthesis at low light intensities.
Plant will grow / survive in the shade / when overshadowed (by taller plants) / when receiving less light;
Note that taller trees are a key feature of a climax community
Succession (AO1)
Reasons for conserving rainforests
1. Conserve / protect
species / plants / animals / organisms
OR For (bio)diversity;
2. Conserve / protect habitats
OR Provides / many habitats ;
3. Reduces climate change;
4. Source of medicines/drugs/wood;
5. Reduces erosion/eutrophication;
6. (For) tourism;
Succession (AO2)
Explain why conservation of habitats frequently involves management of succession.
Prevents a climax community from forming;
Habitats in earlier stage ofsuccession may be better for some species;
E.g. ground nesting birds on heather moorland
Inheritance (AO1)
Phenotype
Expression of genetic constitution / genotype / allele(s);
AND its interaction with the environment;
Inheritance (AO1)
Dominant allele
Is always expressed / shown
in the phenotype;
Inheritance (AO1)
Recessive allele
Requires both alleles to be present - homozygous recessive genotype - to be expressed / show in the phenotype.
Inheritance (AO1)
Genotype
The genetic constitution of an organism.
In other words, all the alleles it contains
e.g. Heterozygous OR homozygous recessive
Inheritance (AO1)
Define a gene
A sequence of DNA bases that codes for a protein
Inheritance (AO1)
Define an allele
Different versions of the same gene
These are typically created by random mutations
Inheritance (AO1)
There may be many _____________ of a single gene.
alleles
Inheritance (AO1)
In a diploid organism, the alleles at a specific __________ may be either homozygous or heterozygous.
locus
Inheritance (AO1)
Define locus
The location/position of a particular gene on a chromosome
Inheritance (AO1)
If there the two copies of a gene are the same allele in a genotype, this is known as __________________
homozygous
Inheritance (AO1)
If there the two copies of a gene are different alleles in a genotype, this is known as __________________
heterozygous
Inheritance (AO1)
What is the expected phenotypic ratio if your cross heterozygous parents (i.e. they carry the recessive allele) in a monohybrid cross?
3 : 1
Where 1 represents the phenotype from the homozygous recessive genotype
Inheritance (AO2)
A breeder crossed a black male cat with a black female cat on a number of occasions. The female cat produced 8 black kittens and 4 white kittens.
Explain the evidence that the allele for white fur is recessive.
Parents are heterozygous;
Accept carriers / carries white allele
Kittens receive white allele from parents / black cat;
Inheritance (AO2)
A breeder crossed a black male cat with a black female cat on a number of occasions. The female cat produced 8 black kittens and 4 white kittens.
Predict the likely ratio of colours of kittens born to a cross between this black male and a white female.
1:1
A Bb (Black) x bb (White) cross will produce Bb and bb offspring
Inheritance (AO1)
- Bb / suitable equivalent;
- Both parents have bar eyes, but have some offspring with round eyes, so parents must be carriers of recessive allele for round eyes;
Inheritance (AO2)
Unaffected parents have affected children
e.g. 3 and 4 produce affected offspring (9 and 11);
Both 3 and 4 are carriers / heterozygous;
Inheritance (AO2)
Evidence
3 and 4 / two Rhesus positives produce Rhesus negative child / children / 7 / 9;
Explanation
Both Rhesus positives / 3 and 4 carry recessive (allele) / are heterozygous / if Rhesus positive was recessive, all children (of 3 and 4) would be Rhesus positive / recessive;
Inheritance (AO2)
In fruit flies, a gene for body colour has a dominant allele for grey body, G, and a recessive allele for black body, g.
Explain how you would determine if the genotype of a grey is homozygous or heterozygous for body colour (2 marks).
1. Cross with a homozygous recessive black fly (with the gg genotype)
2. If some offspring are black, then must be heterozygous/Gg
OR if all offspring are grey, then must be homozygous/GG
Inheritance (AO1)
Codominance
Inheritance (AO1)
What is the expected phenotypic ratio if your cross heterozygous parents for a codominant phenotype.
1 : 2 : 1
Inheritance (AO1)
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.
Suggest two reasons why.
- Small sample size;
- Fusion / fertilisation of gametes is random;
- Linked genes;
- Epistasis;
- Lethal genotypes;
Inheritance (AO2)
- Animal 2 / 5 has hair but offspring do not;
- So 2 / 5 parents must be heterozygous / carriers;
OR
- 4 / 7 / 8 are hairless but parents have hair;
- So 2 / 5 must be heterozygous / carriers;
Inheritance (AO1)
Gametes produced by AaBb genotype.
The genes are on different chromosomes.
AB , Ab , aB , ab
Inheritance (AO1)
Gametes produced by the AABb genotype.
The genes are on different chromosomes.
AB , Ab
There would be x2 AB and x2Ab following meiosis
Inheritance (AO1)
Gametes produced by the ccdd genotype.
The genes are on different chromosomes.
cd
There would be x4 cd gametes following meiosis
Inheritance (AO1)
Expected phenotypic ratio of offspring if both parents are heterozygous in a dihybrid cross.
i.e. AaBb x AaBb
9 : 3 : 3 : 1
Inheritance (AO1)
Mutation is one cause of genetic variation in organisms.
Give two other causes of genetic variation.
1. Crossing over;
2. Independent segregation
(of homologous chromosomes);
3. Random fusion of gametes
OR random fertilisation;
Inheritance (AO1)
What process during meiosis 1 creates different combinations of alleles in the gametes?
Independent segregation
Inheritance (AO2)
1. Large number of eggs / offspring / flies (therefore) improves reliability / can use statistical tests / are representative
2. Small size / (breed) in small flasks / simple nutrient medium (therefore) reduces costs / easily kept / stored;
3. Size / markings / phenotypes (therefore) males / females easy to identify;
4. Short generation time / 7 - 14 days / develop quickly / reproduce quickly (therefore) results obtained quickly / saves times / many generations;
Inheritance (AO1)
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how (6 marks).
(Crossing over)
1. Homologous chromosomes pair up / bivalents form;
- Crossing over / chiasmata form;
- Produces new combination of alleles;
(Independent segregation)
4. Homologous chromosomes separate;
- At random;
- Produces varying combinations of chromosomes / genes / alleles;
- Sister chromatids separated at meiosis II;
Inheritance (AO1)
If two genes are linked on the same chromosome, what gametes would be produced by the AaBb genotype?
AB , ab
These are the known as the ‘parental’ gametes
Inheritance (AO1)
If two genes are linked on the same chromosome, what gametes would be produced by the AABb genotype?
AB , Ab
These are the known as the ‘parental’ gametes
Inheritance (AO1)
Which process during meiosis 1 produces recombinant gametes?
crossing over
Inheritance (AO1)
If two genes are linked on the same chromosome but crossing over occurs, what gametes would be produced by the AaBb genotype?
Also, identify which gametes that would be produced in higher numbers.
More of the ‘parental’ gametes = AB & ab
Less of the ‘recombinant’ gametes = Ab & aB
Inheritance (AO1)
For two linked genes on the same chromosomes, why are fewer recombinant gametes produced by crossing over?
Crossing over is a rare event
Inheritance (AO1)
In fruit flies, the genes for body colour and wing length are linked. Explain what this means.
Genes are on the same chromosome
Inheritance (AO2)
1. The two genes are linked;
2. No crossing over (occurs);
3. No Gl and no gL (recombinant gametes produced)
OR Only GL and gl (parental gametes produced);
OR No Ggll and no ggLl (offspring produced)
Inheritance (AO1)
Alport syndrome results from a sex-linked mutation.
In a male with AS, where would the sex-linked mutation be located?
Tick (✓) one box.
Box 4 - The non-homologous section of an X chromosome
Inheritance (AO2)
In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r.
Male fruit flies are more likely than female fruit flies to have white eyes.
Explain why.
1. Males only have one allele
2. Females need two recessive alleles
OR Females must be homozygous recessive
OR Females could be heterozygous/carriers;
Inheritance (AO2)
What typical pattern of inheritance would likely indicate that a gene is sex-linked?
Explain why.
Unaffected fathers have affected sons;
Explanation:
Sons inherit their x chromosome from their mother;
If mum is a carrier of a recessive allele, she will pass this onto her son who only needs 1 copy of allele for it to be expressed in the phenotype;
In family trees, it is more common for males to have the disease / affected phenotype;
Inheritance (AO2)
Use evidence from the below diagram to explain that hairlessness is caused by a gene on the X chromosome.
Hairless males have fathers with hair OR
4 is hairless but 1 is hairy OR
7 and / or 8 are hairless but 6 is hairy OR
only males are hairless
This is an example of unaffected fathers have affected sons
Inheritance (AO2)
How could you prove a dominant allele is NOT sex-linked?
Explain why.
CLUE = mums & sons
If the allele is sex-linked, homozygous recessive mothers will always have sons that show the recessive phenotype.
If, however, the sons show a dominant phenotype, there is no way he could have inherited this on the X chromosome from his mother.
The dominant allele must be on another chromosome.
Inheritance (AO2)
How could you prove a recessive allele is NOT sex-linked?
Explain why.
CLUE = dads & daughers
If the recessive allele is sex-linked, unaffected fathers will always have unaffected daughters
The father will always pass on the dominant allele to his daughter who would therefore be unaffected.
If, however, the daugher does show a homozygous recessive phenotype, the recessive allele must be on another chromosome.
Inheritance (AO2)
- (Individual) 2 has colour vision but 4 is colour blind / 10 has colour vision but 12 is colour blind
OR 4/12 is colour blind but parents have colour vision;
- So 2/10 must be heterozygous/carriers;
Inheritance (AO2)
Explain one piece of evidence from the below diagram which shows that the gene is NOT on the X chromosome.
Evidence (Mums & Sons)
3 would not be / is Rhesus positive / would be Rhesus negative is sex-linked;
Explanation
3 would receive Rhesus negative (allele) on X (chromosome) from mother / 3 could not receive Rhesus positive (allele) from mother / 3 would not receive Rhesus positive (allele)
OR
Evidence (Dads & Daughters)
9 would be Rhesus positive / would not be / is Rhesus negative / 8 and 9 / all daughters of 3 and 4 would be Rhesus positive;
Explanation
As 9 would receive X chromosome / dominant allele from father / 3;
Inheritance (AO2)
- Animal 2 / 5 has hair but offspring do not;
- So 2 / 5 parents must be heterozygous / carriers;
OR
- 4 / 7 / 8 are hairless but parents have hair;
- So 2 / 5 must be heterozygous / carriers;
Inheritance (AO2)
Epistasis
Inheritance (AO2)
Epistasis
Inheritance (AO2)
Cannot make (active) enzyme A (which converts precursor to linamarin) / cannot make linamarin;
Inheritance (AO2)
no enzyme coded for when no dominant / E allele;
phaeomelanin not converted – (remains yellow);
Inheritance (Maths)
When to use the chi squared test?
To test if there is a significant difference between the observed AND expected numbers in an investigation with categorical data
Inheritance (AO1)
Which statistical test could the scientist use to determine whether his observed results were significantly different from the expected results?
Give the reason for your choice of statistical test.
- Chi squared test;
- Categorical data.
Inheritance (Maths)
What do the compontents of the chi squared equation represent?
Inheritance (Maths)
Inheritance (Maths)
When using the chi squared test, how do you calculate the degrees of freedom?
n - 1
Where ‘n’ represents the number of categories / groups / phenotypes
Inheritance (Maths)
When using the chi squared test, how do you calculate the degrees of freedom?
n - 1
Where ‘n’ represents the number of categories / groups / phenotypes
Inheritance (Maths)
There are 4 possible phenotypes with expected and observed results, calculate the degrees of freedom?
3
As degrees of freedom = n - 1
(where n represents the number of categories / phenotypes)
Inheritance (Maths)
There are 3 possible phenotypes with expected and observed results. Use this information to determine the critical value from the table below.
2 degrees of freedom;
Critical value = 5.99
(when P = 0.05)
Inheritance (AO3)
Following a genetic cross involving 4 possible phenotypes, researchers obtained a chi squared value of 2.32.
Use the table below to state what you can conclude from this data.
The chi squared value is SMALLER than the critical value of 7.82 (when P = 0.05);
There is NO SIGNIFICANT DIFFERENCE
(between the observed and expected values)
There is more than a 5% probability the differences are due to chance.
Inheritance (AO3)
Following a genetic cross involving 2 possible phenotypes, researchers obtained a chi squared value of 4.07.
Use the table below to state what you can conclude from this data.
The chi squared value is LARGER than the critical value of 3.84 (when P = 0.05);
There is a SIGNIFICANT DIFFERENCE
(between the observed and expected values);
There is less than a 5% probability the differences are due to chance;
Populations (AO1)
Define gene pool
All the alleles in a population
Populations (AO1)
Define allele frequency
How often an allele occurs in a population.
Usually given as a percentage of the total population, e.g. 35%, or a decimal, e.g. 0.35.
Populations (AO1)
What does the Hardy-Weinberg principle predict?
The frequency of alleles (of a particular gene);
Will stay constant from one generation to the next / over generations
Providing there are no mutations / no selection / population large / population genetically isolated / mating at random / no migration;
Populations (AO1)
Hardy Weinberg equation
for allele frequency
Populations (AO1)
If the frequency of a dominant allele is 0.72, what is the frequency of the recessive allele?
p + q = 1.0
0.72 + q = 1.0
q = 0.28
Populations (AO1)
Hardy Weinberg equation
for genotype frequency
Populations (Maths)
For a gene with two alleles, B and b. Consider a population of 1000 people, where 300 are homozygous dominant (BB), 500 are heterozygous (Bb) and 200 are homozygous recessive (bb).
Calculate the allele frequency of B and b.
The total number of alleles is: 1000 x 2 = 2000
The number of B alleles: (300 x 2) + (500 x 1) = 1100
Frequency of the B allele: 1100 / 2000 = 0.55
The number of b alleles is: (200 x 2) + (500 x 1) = 900
Frequency of the b alleles: 900 / 2000 = 0.45
p + q = 1.0
0.55 + 0.45 = 1.0
Populations (AO2)
The scientists concluded that the observed frequencies of the phenotypes differed significantly from the expected frequencies.
Use your knowledge of the Hardy–Weinberg principle to suggest two reasons why.
- Selection (against/phenotype/allele);
- (High rate of) mutation;
- Immigration/emigration;
- No random mating.
Populations (AO2)
In mice, one type of disease is inherited as a dominant allele. Would the Hardy–Weinberg principle hold true for a population of mice, some of which had this disease?
Explain your answer
(No)
1. Mice with disease will be unlikely
to reproduce/survive
OR Mice with disease will be selected against;
2. Will not pass on allele (for disease)
OR Allele frequency (for disease) will reduce;
(Yes)
3. As long as the disease did not
affect the mice’s ability to reproduce/survive;
4. The allele frequency will remain constant/not
change;
Populations (Maths)
Populations (Maths)
A population of fruit flies contained 64% grey-bodied flies (Genotype is GG or Gg).
Use the Hardy–Weinberg equation to calculate the percentage of flies heterozygous for gene G.
Populations (Maths)
Populations (Maths)
Evolution may lead to speciation (AO1)
Define gene mutation
1. Random change in the base sequence of DNA.
2. Results in the formation of a new allele.
Evolution may lead to speciation (AO1)
TRUE or FALSE:
Mutations arise spontaneously during DNA replication
TRUE
Evolution may lead to speciation (AO1)
Random mutations are changes to the DNA base sequence that produce new ___________.
alleles
Evolution may lead to speciation (AO1)
Types of mutation
Substitution
Addition
Deletion
Inversion
Duplication
Translocation
Non-disjunction
Evolution may lead to speciation (AO1)
Primary souce of genetic variation
random mutations
Evolution may lead to speciation (AO1)
TRUE or FALSE:
Creating new combinations of alleles does not contribute to genetic variation
FALSE
Evolution may lead to speciation (AO1)
Processes that create new combinations of alleles (and therefore genetic variation)
Independent segregation;
Crossing over;
Random fusion of gametes
Evolution may lead to speciation (AO1)
Describe and explain which processes - other than mutations - that result in increases in genetic variation within a species (4 marks).
1. Independent segregation of homologous
chromosomes/pairs;
2. Crossing over between homologous
chromosomes/pairs (non-sister chromatids);
3. Random fertilisation of gametes;
4. (Produces) new combinations of alleles;
Evolution may lead to speciation (AO1)
Variation which is caused predominantly by genetic factors produces [1] data and is usually caused by a [2] gene.
[1] categorical
[2] single*
*The single gene may have multiple alleles
Evolution may lead to speciation (AO1)
TRUE or FALSE:
Individuals within a population show a wide range of variation in phenotype due to genetic AND environmental factors.
TRUE
Evolution may lead to speciation (AO1)
Phenotypes that are controlled by more than one gene and environmental factors typically produce a __________ distribution.
normal
Evolution may lead to speciation (AO1)
Sources of phenotypic diversity
Mutations that create new alleles
Crossing over
Independent segregation
Random fusion of gametes
Epigenetics
Evolution may lead to speciation (AO1)
Biotic factors that act as
selective pressures
Predation
Disease
Interspecific competition
Evolution may lead to speciation (AO1)
Abiotic factors that act as selection pressures
Temperature
Light intensity
Carbon dioxide concentration
Soil pH
Salinity
Humidity
Windspeed
Evolution may lead to speciation (AO1)
TRUE or FALSE:
Organisms develop advantageous phenotypes because of a change in the environment.
FALSE
Random mutations produce phenotypic variation, then SELECTED FOR/AGAINST
Evolution may lead to speciation (AO1)
Random mutations create new [1] that increases [2]
[1] alleles
[2] variation
Evolution may lead to speciation (AO1)
TRUE or FALSE:
Having large variation in a phenotype of a population enables a species to adapt in response to changes in the environment
TRUE
Evolution may lead to speciation (AO1)
Bullet point the key mark points for natural selection (5 marks).
- Random mutations produce phenotypic variation (within a population)
- (Named) selection pressure in the environment (biotic or abiotic)
- Organisms with (named) advantegous phenotypes are more likely to survive AND reproduce
- Pass on advantageous alleles to the next generation
- Fequency of advantageous allele increases over many generations in the gene pool
Evolution may lead to speciation (AO1)
Selection that favours one
extreme phenotype
Directional
Evolution may lead to speciation (AO1)
Directional selection examples
Antibiotic resistance
Giraffe neck length
Peppered moth
Evolution may lead to speciation (AO1)
Type of selection that favours the mean / most common phenotype
Stabilising
Evolution may lead to speciation (AO1)
Stabilising selection examples
Newborn / baby birthweight
Number of eggs in a birds nest
Evolution may lead to speciation (AO1)
Type of selection that favours both extreme phenotypes
Disruptive
Evolution may lead to speciation (AO1)
Type of selection that reduces variation and therefore the opportunity for evolutionary change
Stabilising
Evolution may lead to speciation (AO1)
Types of selection that brings about evolutionary change
Directional
Disruptive
Evolution may lead to speciation (AO2)
Clostridium difficile is a bacterial species that causes disease in humans.
Antibiotic-resistant strains of C. difficile have become a common cause of infection acquired when in hospital.
Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria becoming a common cause of infection acquired when in hospital (3 marks).
1. (Some bacteria have) random mutations produce alleles for resistance;
2. More antibiotics used in hospital (compared with elsewhere) and exposure to antibiotics is the selection pressure
3. Resistant bacteria survive & reproduce;
4. Pass on resistance allele to next generation
5. high frequency of resistance allele over many generations (in bacterial population);
Evolution may lead to speciation (AO2)
Lactose is the main sugar in milk and is hydrolysed by the enzyme lactase. Lactase is essential to newborn mammals as milk is their only source of food. Most mammals stop producing lactase when they start feeding on other food sources. Humans are an exception to this because some continue to produce lactase as adults. The ability to continue producing lactase is known as lactase persistence (LP) and is controlled by a dominant allele.
One hypothesis for LP in humans suggests that the selective pressure was related to some human populations farming cattle as a source of milk.
Describe how farming cattle as a source of milk could have led to an increase in LP (4 marks).
1. LP allele due to random mutation;
2. Milk provides named nutrient /
e.g. glucose, galactose, protein and its presence act as selection pressure
3. Individuals with LP more likely to survive and reproduce
4. Pass on LP allele to next generation
5. Frequency of LP allele increases
(in the offspring/next generation);
6. This is an example of directional selection;
Evolution may lead to speciation (AO1)
Type of selection that can lead to speciation
Disruptive
Evolution may lead to speciation (AO1)
All new species evolve from existing species via a process known as ____________.
speciation
Evolution may lead to speciation (AO1)
Species key features
1. Capable of interbreeding to produce fertile offspring.
2. Same genes but different alleles.
3. (May show a) wide range of variation in phenotype.
Evolution may lead to speciation (AO1)
Types of speciation
Allopatric
Sympatric
Evolution may lead to speciation (AO1)
Reproductive ____________ is required for speciation.
isolation
Evolution may lead to speciation (AO1)
In allopatric speciation, what causes reproductive isolation?
A geographical barrier
(e.g. river, mountain, road)
Evolution may lead to speciation (AO2)
Describe and explain how a river separating two populations of lemurs can result in new specieis (5 marks).
1. Allopatric speciation;
2. River leads to reproductive isolation
OR No gene flow
OR Gene pools separate;
3. Variation due to random mutations (in different populations);
4. Different selection pressures (either side of the river);
OR Different environmental/abiotic conditions/factors;
5. (Different/advantageous) allele/s passed on/selected OR change in frequency of alleles;
6. (Eventually different species either side of river) cannot interbreed to produce fertile offspring;
Evolution may lead to speciation (AO1)
In sympatric speciation, what causes reproductive isolation?
Random mutations may cause change in behaviour e.g. feeding or mate preferences / timings
Evolution may lead to speciation (AO1)
TRUE or FALSE:
In sympatric speciation, reproductive isolation still occurs despite the species occupying the same habitat / area.
TRUE
Evolution may lead to speciation (AO2)
Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different.
Using this information, suggest how these two species of palm tree arose by sympatric speciation (5 marks).
**1. ** Occurs in the same habitat / environment / population / place;
2. Random mutation/s cause different flowering times;
3. Reproductive isolation
OR No gene flow
OR Gene pools remain separate;
4. Different allele/s passed on / selected
OR Change in frequency of allele/s
5. Eventually different species cannot interbreed to produce fertile offspring;
6. Example of disruptive selection;
Evolution may lead to speciation (AO1)
Genetic drift
Random increase OR decrease in allele frequency due to chance events
Evolution may lead to speciation (AO1)
Events that lead to genetic drift
Natural disasters such as volcanic eruption or being trampled
Evolution may lead to speciation (AO1)
What size of population is vulnerable to genetic drift
Small
Evolution may lead to speciation (AO1)
Explain why small populations are vulnerable to genetic drift.
Random loss of individuals with certain alleles;
Individuals that survive will then reproduce;
Pass on alleles to next generation;
Results in a large change in the frequency of alleles (in a shorter period of time);
Evolution may lead to speciation (AO1)
Contrast genetic drift vs.
natural selection
Natural selection involves differential survival and reproduction of organisms in response to selection pressures whereas genetic drift is not influenced by environmental pressures or the relative advantage of alleles.
Genetic drift is a random change in allele frequency whereas natural selection isn’t
