Genetics, Populations, Evolution & Ecosystems (3.7) Flashcards
Populations in ecosystems (AO1)
Define an abiotic factor
A non-living / physical / chemical factor
Populations in ecosystems (AO1)
List examples of abiotic factors
soil pH
temperature
salinity (concentration of salt)
carbon dioxide concentration
humidity
light intensity
Populations in ecosystems (AO1)
Define a biotic factor
Living / biological factor
Populations in ecosystems (AO1)
List examples of biotic factors
predator
prey / food
disease
presence of opposite sex
Populations in ecosystems (AO1)
Define a population
Groups of organisms of the same species living in the same habitat / ecosystem at the same time;
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 a 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)
Different species occupy different ecological niches.
Explain the advantage of 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)
Define an ecosystem
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 is used to describe populations of different species living in the same habitat?
Community
Populations in ecosystems (AO1)
Describe what typical patterns emerge when plotting the population sizes of predators and their prey over time.
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)
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 (5 marks).
1. Use a grid
2. Method of obtaining random coordinates/numbers e.g. random numbers generator;
3. Count number/frequency in a quadrat;
4. Large sample (20 or more) and calculate mean number (per quadrat/section);
5. Valid method of calculating total number of sundews, e.g. mean number of plants per m2 multiplied by number of m2 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. Method of randomly determining position (of quadrats) e.g. random numbers generator;
2. Large number of quadrats (20 or more);
3. Divide total percentage by number of quadrats;
Populations in ecosystems (AO1)
Describe how the mark-release-recapture method could be used to determine the population of A. aegypti (a species of mosquito) at the start of the investigation (3 marks).
1. Capture sample, mark and release;
2. Leave time for mosquitoes to disperse before second sampling / collection;
3. (Population =) number in first sample × number in second sample divided by number of marked in second sample / number recaptured;
3. Accept: correct equation.
Populations in ecosystems (AO1)
Outline a method the ecologists could have used to determine the plant species richness at one site (3 marks).
- A method of selecting sampling sites at random;
- Use of quadrat;
- Identify (plant) species (at site / in each quadrat)
OR Count number of different plant species in each quadrat / site;
Reject refs to % cover, or counting individuals
Species richness = all the different species (AS content)
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 (AO1)
In addition to a quadrat, what piece of equipment do you need to undertake systematic sampling?
A line / belt transect
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 / stated intervals;
- Using a quadrat;
- Count numbers / percentage cover of dandelions;
- Use several transects;
Populations in ecosystems (AO1)
_______________ are dynamic systems.
Ecosystems
This means they change over time, for example, due to succession
Populations in ecosystems (AO1)
What is the general name of the species that first colonises an inhospitable environment (e.g. barren rock or a sand dune).
Pioneer species
Populations in ecosystems (AO1)
What is the function of pioneer species during primary succession
Changes the environment;
e.g. adds more humus ; adds nitrates to soil;
(humus = the formation of a thin / basic layer of soil)
This makes it less hostile for a new species to colonise the environment
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 (AO1)
Suggest one precaution needed when marking the pine martens (during mark, release & recapture) to make sure the estimate of the number of pine martens is valid (1 mark).
(Marking) does not affect survival/predation/recapture (of the pine marten);
OR
Mark does not rub/wash off/is non-toxic.
Populations in ecosystems (AO1)
What are the assumptions made when using the the mark-release-recapture method to make valid estimates of population size?
- 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 - The marking should not rub off or be lost
- The marked organisms have enough time to (randomly) disperse/distribute into the rest of the population
- Sample population is large enough
Populations in ecosystems (AO1)
What is the final stage of primary succession called?
Climax community
Populations in ecosystems (AO1)
Succession occurs in natural ecosystems.
Describe and explain how succession occurs (5 marks).
- (Colonisation by) pioneer (species);
- 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) - Enables other species to colonise / survive;
- Increase in biodiversity;
- Stability increases / less hostile environment;
- Climax community;
Populations in ecosystems (AO2)
Crabgrass
Populations in ecosystems (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)
Populations in ecosystems (AO1)
What are characteristics of pioneer species?
Photosynthesise;
Fix nitrogen;
Asexual reproduction;
Tolerance to hostile environments;
Populations in ecosystems (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);
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)
(Increase in) dead organisms / humus / decomposition;
Leading to (increase in) nitrification / ammonia to nitrate / activity of nitrifying bacteria;
Populations in ecosystems (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
Populations in ecosystems (AO2)
- Beach grass is the pioneer (species);
- Pioneers/named species change the (abiotic) environment/habitat/conditions/factors;
Must convey idea of change being caused by a species
Accept example of change e.g. more humus
- (So) less hostile for named species OR
(So) more suitable for named species; - Conifer/hardwood trees represent climax community;
Populations in ecosystems (AO1)
Suggest two reasons for conserving rainforests.
1. Conserve/protect
species/plants/animals/organisms
OR For (bio)diversity;
2. Conserve/protect habitats/niches
OR
Provides/many habitats/niches;
3. Reduces climate change;
4. Source of medicines/drugs/wood;
5. Reduces erosion/eutrophication;
6. (For) tourism;
Populations in ecosystems (AO1)
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)
Codominance
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 (AO1)
What is meant by the term phenotype?
Expression of genetic constitution / genotype / allele(s);
AND its interaction with the environment;
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 (AO1)
What is meant by codominant alleles?
Both alleles expressed in the phenotype (if both are present);
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 (AO1)
What is the expected phenotypic ratio if your cross heterozygous parents for a codominant phenotype.
1 : 2 : 1
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 (AO1)
Dominant allele
Is always expressed / shown
in the phenotype;
Inheritance (AO1)
Explain what is meant by a recessive allele.
Requires both alleles to be present (homozygous recessive genotype) to be expressed / show in the phenotype.
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)
What is meant by the term genotype?
The genetic constitution of an organism.
In other words, all the alleles it contains
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 (AO2)
Evidence (not a mark)
3 and 4 / two Rhesus positives produce Rhesus negative child / children / 7 / 9;
Explanation (not a mark)
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 (AO1)
What gametes will the genotype of AaBb produce?
The genes are on different chromosomes.
AB , Ab , aB , ab
Inheritance (AO1)
What gametes will the genotype AABb produce?
The genes are on different chromosomes.
AB , Ab
There would be x2 AB and x2Ab following meiosis
Inheritance (AO1)
What gametes will the genotype ccdd produce?
The genes are on different chromosomes.
cd
There would be x4 cd gametes following meiosis
Inheritance (AO1)
What is the expected phenotypic ratio of the offspring if both parents are heterozygous in a dihybrid cross.
i.e. AaBb x AaBb
9 : 3 : 3 : 1
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.
- Males have one allele;
Accept males only need one allele.
- Females need two recessive alleles
OR Females must be homozygous recessive
OR Females could be heterozygous/carriers;
Inheritance (AO1)
Mutation is one cause of genetic variation in organisms.
Give two other causes of genetic variation.
- Crossing over;
- Independent segregation/assortment (of homologous chromosomes);
- Random fusion of gametes
OR random fertilisation;
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 (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)
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)
Which process during meiosis 1 produces recombinant gametes?
crossing over
Inheritance (AO1)
For two genes of different chromosomes, a person with the genotype AaBb produces gametes AB, Ab, aB and ab.
What process during meiosis 1 creates these different combinations of alleles in the gametes?
Independent segregation
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 (AO2)
Epistasis
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 (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 (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)
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)
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)
- Large number of eggs / offspring / flies (therefore) improves reliability / can use statistical tests / are representative / large sample (size)
- Small size / (breed) in small flasks / simple nutrient medium (therefore) reduces costs / easily kept / stored;
- Size / markings / phenotypes (therefore) males / females easy to identify;
- Short generation time / 7 - 14 days / develop quickly / reproduce quickly (therefore) results obtained quickly / saves times / many generations;
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)
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 / 4 is hairless but 1 is hairy / 7 and / or 8 are hairless but 6 is hairy / only males are hairless;
This is an example of unaffected fathers have affected sons
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 (not a mark)
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 (not a mark)
As 9 would receive X chromosome / dominant allele from father / 3;
Inheritance (AO2)
Cannot make (active) enzyme A (which converts precursor to linamarin) / cannot make linamarin;
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 (AO2)
- The (two) genes are linked
OR autosomal linkage; - No crossing over (occurs) OR (Linked) genes are close together;
- 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 (AO2)
no enzyme coded for when no dominant / E allele;
phaeomelanin not converted – (remains yellow);
Inheritance (Maths)
What can the chi squared test be used to test for?
If there is a significant difference between the observed AND expected numbers in an investigation.
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)
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)
What is the 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)
What is the 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)
Random mutations are changes to the DNA base sequence that produce new ___________.
alleles
Evolution may lead to speciation (AO1)
Which processes create new combinations of alleles and therefore genetic variation?
Independent segregation;
Crossing over;
Random fusion of gametes
Evolution may lead to speciation (AO1)
Which processes 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)
Which biotic factors provide selective pressures during natural selection?
Predation;
Disease;
Interspecific competition;
Evolution may lead to speciation (AO1)
Which abiotic factors provide selective pressures during natural selection?
Temperature
Light intensity
Carbon dioxide concentration
Soil pH
Salinity
Humidity
Windspeed
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)
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)
Which type of selection favours one extreme phenotype?
Directional
Evolution may lead to speciation (AO1)
Which type of selection favours the mean / most common phenotype?
Stabilising
Evolution may lead to speciation (AO1)
Which type of selection favours both extreme phenotypes?
Disruptive
Evolution may lead to speciation (AO1)
Which type of selection reduces variation and therefore the opportunity for evolutionary change?
Stabilising
Evolution may lead to speciation (AO1)
Which types of selection 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. (Exposure to) antibiotics is the selection pressure
OR Resistant bacteria survive & reproduce;
OR Non-resistant bacteria die
3. More antibiotics used in hospital (compared with elsewhere)
OR (So) high frequency of resistance allele (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. Directional selection;
2. LP due to random mutation
OR Allele for LP due to rando, mutation;
3. Milk provides named nutrient /
e.g. glucose, galactose, protein
4. Individuals with LP more likely to survive and reproduce
OR Individuals with advantageous allele more likely to survive and reproduce;
Accept ‘pass on allele/LP for reproduce.
5. Frequency of LP allele increases
(in the offspring/next generation);
Evolution may lead to speciation (AO1)
Which type of selection 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)
What are the key features of a specieis?
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)
What are the two 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.
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;
OR Different environmental/abiotic conditions/factors;
5. (Different/advantageous) allele/s passed on/selected OR change in frequency of alleles;
6. (Eventually different species) 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.
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. Disruptive (natural) selection;
Evolution may lead to speciation (AO1)
What is genetic drift?
Random increase OR decrease in allele frequency
Evolution may lead to speciation (AO1)
What events can 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);
