Year 13: 7. Genetics, populations, evolution & ecosystems Flashcards
Describe the process of succession (6)
- (Colonisation by) pioneer species;
- Pioneers cause change in environmental abiotic / biotic factors(give an example);
- Pioneers make the environment less hostile for new species;
- New species change/make conditions less suitable for previous species;
- Change/increase in diversity/biodiversity;
- Stability increases [population/richness/abiotic factors];
- Climax community;
Explain how succession results in a wide variety of fish living on coral reefs. (2)
- Increase in variety/diversity of species/plants/animals; OR Increase in number of species/populations; OR Increase in species richness / biodiversity
- Provides more/different habitats/niches OR Provides greater variety/types of food OR becomes less hostile;
Describe random sampling
[estimation of population density]
- Use a grid / split area into squares/sections;
- Method of obtaining random coordinates / numbers, e.g. calculator/computer/random numbers table/random number generator;
- Count number/frequency of plants in a quadrat;
- Large sample (20+ quadrats) AND Calculate mean/average number (per quadrat/section);
- Valid method of calculating total number of ……… e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in wood;
Describe systematic sampling (3)
- Transect/lay line/tape measure (from one side of the dune to the other);
- Place quadrats at regular intervals along the line;
- Count plants/percentage cover/abundance scale (in quadrats) OR Count plants and record where they touch line/transect;
Describe how you would determine the mean percentage cover for beach grass on a sand dune. (3)
- Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
- Large number/sample of quadrats; (min 20)
- Divide total percentage by number of quadrats/samples/readings;
Describe a method that could be used to determine the mean percentage cover of algae on a coral reef. (3)
- Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
- Large number/sample of quadrats; (>20)
- Divide total percentage by number of quadrats/samples/readings;
Describe the mark, release, recapture technique (4)
- Capture sample, mark and release;
- Appropriate method of marking suggested / method of marking does not harm fish;
- Take second sample and count marked organisms;
- No in No in Population =
(No in sample1 × No in sample2) divided by Number marked in sample2;
The mark-release-recapture method can be used to estimate the size of a fish population.
Explain how.
(4)
- Capture/collect sample, mark and release;
- Ensure marking is not harmful (to fish) OR Ensure marking does not affect survival (of fish);
- Allow (time for) fish to (randomly) distribute before collecting a second sample;
- (Population =) number in first sample × number in second sample divided by number of marked fish in second sample/number recaptured;
Suggest why the mark-release-recapture method can produce unreliable results in very large lakes (2)
- Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;
- Fish may remain in one area OR fish may congregate
Describe how you would determine how many quadrats to use when investigating a habitat. (4)
- Calculate running mean/description of running mean;
- When enough quadrats, this shows little change/levels out (if plotted as a graph);
- Enough to carry out a statistical test;
- A large number to make sure results are reliable;
- Need to make sure work can be carried out in the time available;
Define ‘carrying capacity’
- Maximum number of individuals of each species an ecosystem can support.
Suggest two reasons for conserving rainforests.
- Conserve/protect species/plants/animals/organisms OR For (bio)diversity;
- Conserve/protect habitats/niches OR Provides/many habitats/niches; or conserve land for indigenous communities;
- Reduces climate change;
- Source of medicines/drugs/wood;
- Reduces erosion/eutrophication;
- (For) tourism;
State three causes of genetic variation
- Mutation
- Crossing over
- Independent segregation / assortment (of homologous chromosomes)
- Random fusion of gametes / fertilisation / mating
What is meant by a genome?
- (All) the DNA in a cell/organism;
- ‘(all) the ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
- ‘the total number of DNA bases in a cell/organism’
What is a gene pool?
- All the alleles in a population;
How do multiple alleles of a gene arise?
- mutations;
- which are different / at different positions in the gene;
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; Sex-linkage / crossing over;
- Epistasis;
- Lethal genotypes;
What is meant by a recessive allele?
- Only expressed when homozygous / not expressed in the heterozygote / not expressed if dominant present;
What is meant by a dominant allele?
Always expressed in the phenotype.
What does Hardy Weinberg’s equation predict? [3]
- The frequency/proportion of alleles (of a particular gene);
- Will remain constant from one generation to the next/over generations / no genetic change over time;
- Providing no mutation/no selection/population large/population genetically isolated/mating at random/no migration; (must state 3)
Define gene linkage
- (Genes/loci) on same chromosome;
Define epistasis
- The expression of one allele of one gene affects or masks the expression of another(allele/gene) in the phenotype;
Describe why observed phenotypes don’t match expected values. [3]
- Fertilisation is random OR Fusion of gametes is random;
- Small/not-large population/sample;
- Selection advantage/disadvantage/lethal alleles;
Define codominance
- Both alleles (equally) expressed in the phenotype;
Rules for Dominant alleles
- Affected offspring MUST have at least one affected parent.
- Unaffected parents ONLY have unaffected offspring.
- If both parents are affected and have an unaffected offspring, both parents must be Heterozygous
Rules for recessive alleles
- Unaffected parents can have an affected offspring (if they are Heterozygous)
Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.
- (Recessive) allele is always expressed in males / males have one (recessive) allele;
- Females need two recessive alleles / females need to be homozygous recessive / females could have dominant and recessive alleles / be heterozygous;
Expected offspring phenotype ratios from heterozygous parents:
1. Monohybrid
2. Dihybrid
3. Epistasis
4. Autosomal linkage
Dominant : recessive
- 3:1
- 9:3:3:1
- 9:4:3 or 15:1 or 9:7
- 3:1 (no x over) (no other pattern other than 4 phenotypes with recombination of alleles)
Define sex-linkage
Alleles/genes located on the non-homologous section of an X chromosome
What is meant by the term phenotype?
- (Expression / appearance / characteristic due to) genetic constitution / genotype / allele(s);
- (Expression / appearance / characteristic due to) interaction with environment;
Explain how a single base substitution causes a change in the structure of a polypeptide [3]
- Change in (sequence of) amino acid(s)/primary structure;
- Change in hydrogen/ionic/disulfide bonds;
- Alters tertiary structure;
Define genotype
The genetic constitution of an organism.
All the alleles within an organism.
Which part of the Hardy-Weinberg equation represent the heterozygotes?
2Pq
or
2xPxq
A parent has the following genotype AaBb
Genes A and B are not linked (They are found on different homologous chromosomes)
List all the possible gamete genotypes
AB, Ab, aB, and ab
A parent has the following genotype AaBb
Genes A and B are autosomally linked (They are found on the same homologous chromosomes)
List all the possible gamete genotypes
Larger and similar numbers of
AB & ab
Fewer and similar number of recombinants
aB & Ab
Explain what is meant by the terms totipotent and pluripotent.
- totipotent cells can give rise to a complete human/all cell types;
- pluripotent can only give some cell types;
Explain how cells produced from stem cells can have the same genes yet be of different types. [2]
- {not all / different} genes are switched {on / off} /active / activated ;
- correct and appropriate reference to factors /mechanisms for gene switching ;
- e.g. reference to promoters / transcription factors
Describe the mechanism by which a signal protein causes the synthesis of mRNA. [5]
- signal protein {binds to / joins to / interacts with / activates}
- receptor on surface membrane;
- messenger molecule moves from cytoplasm and enters nucleus;
- {produces / activates} transcription factor;
- binds to promoter region;
- RNA polymerase transcribes target gene;
Explain how oestrogen enables RNA polymerase to transcribe its target gene. [4]
- Oestrogen diffuses through the cell membrane;
- attaches to ERα receptor;
- ERα receptor changes shape;
- ERα receptor leaves protein complex which inhibited it’s action;
- oestrogen receptor binds to promoter region;
- enables RNA polymerase to transcribe target gene.
Compare the structure of dsRNA and DNA. [4]
* Similarities; 2 max
* Polynucleotides/polymer of nucleotides;
* Contain Adenine, Guanine, Cytosine;
* Have pentose sugar/5 carbon sugar;
* Double stranded/hydrogen bonds/base pairs.
* Differences; 2 max
* dsRNA contains uracil, DNA contains thymine;
* dsRNA contains ribose DNA contains Deoxyribose;
* dsRNA is Shorter than DNA; fewer base pairs in length;
Explain how the methylation of tumour suppressor genes can lead to cancer. [3]
- Methylation prevents transcription of gene;
- Protein not produced that prevents cell division / causes cell death / apoptosis;
- No control of mitosis.
Describe how alterations to tumour suppressor genes can lead to the development of tumours. [4]
- (Increased) methylation (of tumour suppressor genes);
- Mutation (in tumour suppressor genes);
- Tumour suppressor genes are not transcribed/expressed
OR - Amino acid sequence/primary/ tertiary structure altered;
- (Results in) rapid/uncontrollable cell division;
Describe what is meant by a malignant tumour. [2]
- mass of undifferentiated / unspecialised / totipotent cells;
- uncontrolled cell division;
- metastasis / (cells break off and) form new tumours /
- spread to other parts of body;
Describe how altered DNA may lead to cancer. [5]
- (DNA altered by) mutation;
- (mutation) changes base sequence;
- of gene controlling cell growth / oncogene / that monitors cell division;
- of tumour suppressor gene;
- change protein structure / non-functional protein / protein not formed;
- (tumour suppressor genes) produce proteins that inhibit cell division;
- mitosis;
- uncontrolled / rapid / abnormal (cell division);
- malignant tumour;
Describe how alterations to tumour suppressor genes can lead to the development of tumours. [4]
- (Increased) methylation (of tumour suppressor genes);
- Mutation (in tumour suppressor genes);
- Tumour suppressor genes are not transcribed / expressed OR Amino acid sequence / primary structure altered;
- (Results in) rapid/uncontrollable cell division;
Define epigenetics
- Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.
Describe how DNA is replicated in a cell.[5]
- DNA strands separate / hydrogen bonds broken;
- Parent strand acts as a template / copied / semi-conservative replication;
- Nucleotides line up by complementary base pairing; (Adenine & Thymine etc)
- Role of DNA polymerase: joins adjacent nucleotides on the developing strand via condensation and formation of phosphodiester bond;
- 5’ to 3’ direction
- Each new DNA molecule has 1 template and 1 new strand
- Formed by semi-conservative replication.
Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment. [4]
- Requires DNA fragment) (Taq) DNA polymerase, (DNA) nucleotides and primers;
- Heat to 95 °C to break hydrogen bonds (and separate strands);
- Reduce temperature (40-65°C) so primers bind to DNA/strands;
- Increase temperature (70 to 75 °C), DNA polymerase joins nucleotides (and repeat method);
Why is the DNA heat to 95°C during PCR? [2]
- Produce single stranded DNA
- Breaks WEAK hydrogen bonds between strands
Why do you add primers during PCR? [3]
- Attaches to / complementary to start of the gene / end of fragment;
- Replication of base sequence from here;
- Prevents strands annealing
What is a Primer?
A short, single stranded DNA base sequence, that is complementary to the start of a target DNA sequence that is to be replicated.
Explain why ‘base-pairs’ is a suitable unit for measuring the length of a piece of DNA. [2]
- DNA = 2 chains / joined by linking of 2 bases / A with T and G with C/ purine pairs with pyrimidine;
- Bases are a constant distance apart / nucleotides occupy constant distance
- each base-pair is same length / sugar-phosphate is a constant distance;
Name one mutagenic agent.
- high energy radiation /ionising particles e.g. named particles/α, β, γ & X-rays;
- benzene;
- x rays/cosmic rays;
- uv (radiation);
- carcinogen / named carcinogen;
- mustard gas / phenols / cigarette tar;
- HPV virus
A deletion mutation occurs in gene 1.
Describe how a deletion mutation alters the structure of a gene. [2]
- removal of one or more bases/nucleotide;
- frameshift/(from point of mutation) base sequence change;
Describe the main stages in the copying, cutting and separation of the DNA. [7]
- heat DNA to 95°C / 90°C;
- strands separate;
- cool so that primers bind to DNA;
- add DNA polymerase/nucleotides;
- use of restriction enzymes to cut DNA at specific base sequence/ breaks phosphodiester bonds
- use of electric current and agar/gel;
- shorter fragments move further;
Describe the polymerase chain reaction. [6]
- Heat DNA so Breaks hydrogen bonds/separates strands;
- Add primers & nucleotides;
- Cool to allow binding of nucleotides/primers;
- Reheat to activate DNA polymerase;
- Role of (DNA) polymerase (described)
- Repeat cycle many times;
Why is the PCR graph exponential [2]
- Number of DNA molecules double each cycle
- Initially start with a low number of DNA molecules
Why does the PCR graph plateau? [2]
Primers are limiting
DNA Polymerase (eventually) denatures
DNA nucleotides are limiting
Suggest one reason why DNA replication stops in the polymerase chain reaction.
Primers are limiting
DNA Polymerase (eventually) denatures
DNA nucleotides are limiting
Suggest why the restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once. [3]
- enzymes only cut DNA at specific base sequence/recognition site/specific point;
- sequence of bases/recognition site/specific point (on which enzyme acts)
- occurs once in plasmid and many times in human DNA;
- (max 1 if no reference to base sequence or recognition site)
What are the 5 stages involved in the recombinant DNA process?
- Isolation (of DNA)
- Insertion (of DNA into Vector)
- Transformation (Vector introduced into Host cell)
- Identification (Determine successfully trangenic / GM organisms)
- Cloning
State 3 techniques to isolate DNA
- mRNA to cDNA using Reverse Transcriptase
- Use Resriction endonuclease enzymes
- Use Gene machine
What is the advantage of using Reverse transcriptase over Restriction enzymes to isolate target DNA? [2]
- mRNA is more abundant in specialised cell / multiple copies of mRNA in cytoplasm WHEREAS Nucleus only has 2 alleles (Diploid)
- mRNA has no introns as they have been spliced / removed by splicing whereas Nuclear genes contain introns
Explain what is meant by a vector.
- Carrier;
- of target / foreign DNA/gene;
- Into cell/other organism/host;
State 2 types of vectors
- Plasmids
- Bacteriophage
- Liposomes
- (Gene gun) off spec
Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected.
- isolate TARGET gene/DNA from another organism/mRNA from cell/organism;
- using restriction endonuclease/restriction enzyme/reverse transcriptase to get DNA;
- produce sticky ends;
- use DNA ligase to join TARGET gene to plasmid;
- also include marker gene; (example of marker e.g. antibiotic resistance);
- add plasmid to bacteria to grow (colonies);
- (replica) plate onto medium where the marker gene is expressed;
- bacteria/colonies not killed have antibiotic resistance gene and (probably) the TARGET gene;
- bacteria/colonies expressing the marker gene have the TARGET gene as well;
Describe how STRs could be removed from a sample of DNA.
- Restriction endonucleases/enzymes;
- (Cut DNA) at specific base sequences/pairs OR (Cut DNA) at recognition/restriction sites;
mRNA may be described as a polymer. Explain why.
- Made up of many (similar) molecules/monomers/nucleotides/units;
What is a DNA probe?
- (Short) single strand of DNA;
- Bases complementary (with DNA/allele/gene);
Name three techniques used by scientists to compare DNA sequences.
- Polymerase Chain Reaction
- DNA fingerprinting
- Gel electrophoresis
What name is used for the non-coding sections of a gene?
- Introns
Where are VNTR’s located?
- Intergenic regions of chromosomes
- (Between adjacent genes on the same chromosome)
Explain why fragments of DNA from cancer cells may be present in blood plasma
- cancer cells die / break open releasing DNA;
Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids.
- Restriction (endonuclease/enzyme) to cut plasmid/vector;
- Ligase joins gene/DNA to plasmid/vector;
Describe how enzymes could be used to insert the GH gene into a plasmid.
- Restriction endonucleases/enzymes cuts plasmid; OR Restriction endonucleases/enzymes produces ‘sticky ends’;
- Reject restriction enzymes cuts the gene.*
- Ligase joins gene/DNA and plasmid OR Ligase joins ‘sticky ends’;
