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Left RSFC Year 13 2022-24 > Year 13: 7. Genetics, populations, evolution & ecosystems > Flashcards

Year 13: 7. Genetics, populations, evolution & ecosystems Flashcards

1
Q

Describe the process of succession (6)

A
  • (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;
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2
Q

Explain how succession results in a wide variety of fish living on coral reefs. (2)

A
  • 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;
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3
Q

Describe random sampling
[estimation of population density]

A
  • 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;
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4
Q

Describe systematic sampling (3)

A
  • 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;
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5
Q

Describe how you would determine the mean percentage cover for beach grass on a sand dune. (3)

A
  • 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;
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6
Q

Describe a method that could be used to determine the mean percentage cover of algae on a coral reef. (3)

A
  • 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;
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7
Q

Describe the mark, release, recapture technique (4)

A
  • 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;
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8
Q

The mark-release-recapture method can be used to estimate the size of a fish population.

Explain how.
(4)

A
  • 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;
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9
Q

Suggest why the mark-release-recapture method can produce unreliable results in very large lakes (2)

A
  • Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;
  • Fish may remain in one area OR fish may congregate
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10
Q

Describe how you would determine how many quadrats to use when investigating a habitat. (4)

A
  • 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;
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11
Q

Define ‘carrying capacity’

A
  • Maximum number of individuals of each species an ecosystem can support.
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12
Q

Suggest two reasons for conserving rainforests.

A
  1. Conserve/protect species/plants/animals/organisms OR For (bio)diversity;
  2. Conserve/protect habitats/niches OR Provides/many habitats/niches; or conserve land for indigenous communities;
  3. Reduces climate change;
  4. Source of medicines/drugs/wood;
  5. Reduces erosion/eutrophication;
  6. (For) tourism;
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13
Q

State three causes of genetic variation

A
  • Mutation
  • Crossing over
  • Independent segregation / assortment (of homologous chromosomes)
  • Random fusion of gametes / fertilisation / mating
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14
Q

What is meant by a genome?

A
  • (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’
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15
Q

What is a gene pool?

A
  • All the alleles in a population;
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16
Q

How do multiple alleles of a gene arise?

A
  • mutations;
  • which are different / at different positions in the gene;
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17
Q

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios.

Suggest two reasons why.

A
  • Small sample size;
  • Fusion/fertilisation of gametes is random;
  • Linked Genes; Sex-linkage / crossing over;
  • Epistasis;
  • Lethal genotypes;
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18
Q

What is meant by a recessive allele?

A
  • Only expressed when homozygous / not expressed in the heterozygote / not expressed if dominant present;
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19
Q

What is meant by a dominant allele?

A

Always expressed in the phenotype.

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20
Q

What does Hardy Weinberg’s equation predict? [3]

A
  • 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)
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21
Q

Define gene linkage

A
  • (Genes/loci) on same chromosome;
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22
Q

Define epistasis

A
  • The expression of one allele of one gene affects or masks the expression of another(allele/gene) in the phenotype;
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23
Q

Describe why observed phenotypes don’t match expected values. [3]

A
  • Fertilisation is random OR Fusion of gametes is random;
  • Small/not-large population/sample;
  • Selection advantage/disadvantage/lethal alleles;
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24
Q

Define codominance

A
  • Both alleles (equally) expressed in the phenotype;
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25
Q

Rules for Dominant alleles

A
  • 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
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26
Q

Rules for recessive alleles

A
  • Unaffected parents can have an affected offspring (if they are Heterozygous)
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27
Q

Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.

A
  • (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;
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28
Q

Expected offspring phenotype ratios from heterozygous parents:
1. Monohybrid
2. Dihybrid
3. Epistasis
4. Autosomal linkage

A

Dominant : recessive

  1. 3:1
  2. 9:3:3:1
  3. 9:4:3 or 15:1 or 9:7
  4. 3:1 (no x over) (no other pattern other than 4 phenotypes with recombination of alleles)
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29
Q

Define sex-linkage

A

Alleles/genes located on the non-homologous section of an X chromosome

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30
Q

What is meant by the term phenotype?

A
  • (Expression / appearance / characteristic due to) genetic constitution / genotype / allele(s);
  • (Expression / appearance / characteristic due to) interaction with environment;
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31
Q

Explain how a single base substitution causes a change in the structure of a polypeptide [3]

A
  • Change in (sequence of) amino acid(s)/primary structure;
  • Change in hydrogen/ionic/disulfide bonds;
  • Alters tertiary structure;
32
Q

Define genotype

A

The genetic constitution of an organism.
All the alleles within an organism.

33
Q

Which part of the Hardy-Weinberg equation represent the heterozygotes?

A

2Pq

or

2xPxq

34
Q

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

A

AB, Ab, aB, and ab

35
Q

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

A

Larger and similar numbers of
AB & ab

Fewer and similar number of recombinants
aB & Ab

36
Q

Explain what is meant by the terms totipotent and pluripotent.

A
  • totipotent cells can give rise to a complete human/all cell types;
  • pluripotent can only give some cell types;
37
Q

Explain how cells produced from stem cells can have the same genes yet be of different types. [2]

A
  • {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
38
Q

Describe the mechanism by which a signal protein causes the synthesis of mRNA. [5]

A
  • 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;
39
Q

Explain how oestrogen enables RNA polymerase to transcribe its target gene. [4]

A
  • 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.
40
Q

Compare the structure of dsRNA and DNA. [4]

A

* 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;

41
Q

Explain how the methylation of tumour suppressor genes can lead to cancer. [3]

A
  • Methylation prevents transcription of gene;
  • Protein not produced that prevents cell division / causes cell death / apoptosis;
  • No control of mitosis.
42
Q

Describe how alterations to tumour suppressor genes can lead to the development of tumours. [4]

A
  • (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;
43
Q

Describe what is meant by a malignant tumour. [2]

A
  • mass of undifferentiated / unspecialised / totipotent cells;
  • uncontrolled cell division;
  • metastasis / (cells break off and) form new tumours /
  • spread to other parts of body;
44
Q

Describe how altered DNA may lead to cancer. [5]

A
  • (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;
45
Q

Describe how alterations to tumour suppressor genes can lead to the development of tumours. [4]

A
  • (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;
46
Q

Define epigenetics

A
  • Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.
47
Q

Describe how DNA is replicated in a cell.[5]

A
  • 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.
48
Q

Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment. [4]

A
  • 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);
49
Q

Why is the DNA heat to 95°C during PCR? [2]

A
  • Produce single stranded DNA
  • Breaks WEAK hydrogen bonds between strands
50
Q

Why do you add primers during PCR? [3]

A
  • Attaches to / complementary to start of the gene / end of fragment;
  • Replication of base sequence from here;
  • Prevents strands annealing
51
Q

What is a Primer?

A

A short, single stranded DNA base sequence, that is complementary to the start of a target DNA sequence that is to be replicated.

52
Q

Explain why ‘base-pairs’ is a suitable unit for measuring the length of a piece of DNA. [2]

A
  • 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;
53
Q

Name one mutagenic agent.

A
  • 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
54
Q

A deletion mutation occurs in gene 1.

Describe how a deletion mutation alters the structure of a gene. [2]

A
  • removal of one or more bases/nucleotide;
  • frameshift/(from point of mutation) base sequence change;
55
Q

Describe the main stages in the copying, cutting and separation of the DNA. [7]

A
  • 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;
56
Q

Describe the polymerase chain reaction. [6]

A
  • 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;
57
Q

Why is the PCR graph exponential [2]

A
  • Number of DNA molecules double each cycle
  • Initially start with a low number of DNA molecules
58
Q

Why does the PCR graph plateau? [2]

A

Primers are limiting
DNA Polymerase (eventually) denatures
DNA nucleotides are limiting

59
Q

Suggest one reason why DNA replication stops in the polymerase chain reaction.

A

Primers are limiting
DNA Polymerase (eventually) denatures
DNA nucleotides are limiting

60
Q

Suggest why the restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once. [3]

A
  • 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)
61
Q

What are the 5 stages involved in the recombinant DNA process?

A
  1. Isolation (of DNA)
  2. Insertion (of DNA into Vector)
  3. Transformation (Vector introduced into Host cell)
  4. Identification (Determine successfully trangenic / GM organisms)
  5. Cloning
62
Q

State 3 techniques to isolate DNA

A
  • mRNA to cDNA using Reverse Transcriptase
  • Use Resriction endonuclease enzymes
  • Use Gene machine
63
Q

What is the advantage of using Reverse transcriptase over Restriction enzymes to isolate target DNA? [2]

A
  • 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
64
Q

Explain what is meant by a vector.

A
  • Carrier;
  • of target / foreign DNA/gene;
  • Into cell/other organism/host;
65
Q

State 2 types of vectors

A
  • Plasmids
  • Bacteriophage
  • Liposomes
  • (Gene gun) off spec
66
Q

Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected.

A
  • 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;
67
Q

Describe how STRs could be removed from a sample of DNA.

A
  1. Restriction endonucleases/enzymes;
  2. (Cut DNA) at specific base sequences/pairs OR (Cut DNA) at recognition/restriction sites;
68
Q

mRNA may be described as a polymer. Explain why.

A
  • Made up of many (similar) molecules/monomers/nucleotides/units;
69
Q

What is a DNA probe?

A
  • (Short) single strand of DNA;
  • Bases complementary (with DNA/allele/gene);
70
Q

Name three techniques used by scientists to compare DNA sequences.

A
  • Polymerase Chain Reaction
  • DNA fingerprinting
  • Gel electrophoresis
71
Q

What name is used for the non-coding sections of a gene?

A
  • Introns
72
Q

Where are VNTR’s located?

A
  • Intergenic regions of chromosomes
  • (Between adjacent genes on the same chromosome)
73
Q

Explain why fragments of DNA from cancer cells may be present in blood plasma

A
  • cancer cells die / break open releasing DNA;
74
Q

Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids.

A
    1. Restriction (endonuclease/enzyme) to cut plasmid/vector;
    1. Ligase joins gene/DNA to plasmid/vector;
75
Q

Describe how enzymes could be used to insert the GH gene into a plasmid.

A
  • 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’;

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