T8: gene expression Flashcards
1
Q
define a gene mutation
A
- a change in the base sequence of DNA
- can arise during DNA replication (interphase)
2
Q
define a mutagenic agent
A
- a factor that increases rate of mutation
- e.g. ultraviolet or alpha particles
3
Q
Explain how a gene mutation can lead to th production of a non-functional protein or enzyme
A
- changes seqence of base triplets in DNA so changes sequence of codons on mRNA
- so changes amino acid seuqnce in the encoded polypeptide
- so changes position of hydrogen/ionic/disulphide bonds between amino acids.
- so changes tertiary structure (shape) of protein
- enzymes - active site changes shape so substrate can’t bind , enzyme substrate complexes cannot form.
4
Q
Describe the 6 different types of gene mutation
A
substitution: Replacement of a base by a different base (in DNA); (1)
addition: 1 or more bases/ nucleotides are added to the DNA base sequene
deletion: nucleotides are lost from the DNA base sequence ( can lead to frame shift)
duplication: a sequence of DNA bases / nucleotides is repeated.
inversion: a sequence of bases detaches from the DNA sequence then rejoins at the same position in the reverse order
translocation: a sequence of DNA bases detaches and is inserted as a different location within the same or a different chromosome
5
Q
Explain why not all gene mutations affect the order of amino acids
A
- some substitutions change only 1 triplet codon which could still code for the same amino acid. As the code is degenerate.
- some occur in introns which do not code for amino acids.
6
Q
Explain why a change in amino acid sequence is not always harmful
A
- may not change tertiary structure of protein ( if position of ionic disulfide and H bonds don’t change.
- may positively change the properties of the protein , giving the organnism a selective advantage
7
Q
Explain what is meant by a frame shift .
A
- occurs when gene mutations change the number of nucelotides + bases by a number not / by 3
- this shifts the way the genetic code is read , so all the DNA triplets / mRNA codons downstream from the mutation change.
8
Q
(i) Suggest how a mutation can lead to the production of a protein that has one amino acid missing. (2)
A
(i) Loss of 3 bases / triplet = 2 marks;;
9
Q
Suggest how the production of a protein with one amino acid missing may lead to a genetic disorder such as Ellis-van Creveld syndrome.
A
1. Change in tertiary structure / active site;
2. (So) faulty / non-functional protein / enzyme;
Accept: reference to examples of loss of function eg fewer E-S complexes formed
10
Q
A mutation in the gene coding for enzyme B could lead to the production of a non-functional enzyme. Explain how. (3)
A
- Change in base sequence (of DNA / gene) leading to change in amino acid sequence / primary structure (of enzyme);
- Change in hydrogen / ionic / disulphide bonds leading to change in the tertiary structure / active site (of enzyme);
3. Substrate not complementary / cannot bind (to enzyme / active site) / no enzyme-substrate complexes form;
11
Q
Explain how a new form of myosin with different properties could have been produced as a result of mutation. (4)
A
- addition / deletion / substitution of a base in DNA of the gene which codes for myosin;
- changes in base sequence in DNA
- change in amino acid sequence / primary structure;
causes a different tertiary structure; - which alters the binding properties of myosin;
12
Q
what are stem cells?
8.2
A
undifferentiated cells capable of :
- dividing by mitosis to replace themselves indefinitely
- differentiating into other types of specialised cells.
13
Q
Describe how stem cells become specialised during development
- how do they obtain a specific function/ differentiate
A
- A stimulus activates specific genes through transcription factors
- transcription of mrna from these genes occurs and are translated into proteins
- which modify the cell’s structure and function, resulting in specialisation.
14
Q
(a) Give two characteristic features of stem cells.
A
- Will replace themselves / keep dividing / replicate;
- Undifferentiated / can differentiate / develop into other cells / totipotent / multipotent / pluripotent;
15
Q
Describe totipotent cells
A
- occur for a limited time in early mammalian embryos.
- can divide and differentiate into any type of body cells ( including extra-embryonic cells) e.g. placenta.
16
Q
Describe pluripotent cells
A
- found in mammalian embryos ( after first few cell division)
- can divide and differentiate into most cell types ( every cell type in the body but not placenta)
17
Q
Describe multipotent cells
A
- found in mature mammals
- can divide + differentiate into a limited number of cell types
- e.g. in bone marrow which can differentiate into types of blood cells.
18
Q
Describe unipotent cells , using an example
A
- found in mature mammals
- can divide and differentiate into just one cell type
- E.G. Unipotent cells in the heart can divide and differentiate into cardiomyocytes
19
Q
what are meristem cells
A
- undifferentiated cells found in the tips of roots and shoots.
- able to rapdily divide and produce a new plant
20
Q
Explain how stem cells can be used in the treatment of human disorders
A
- transplanted into patients to divide in unlimited numbers.
- then differentiate into required healthy cells ( to replace faulty/damaged cells)
- e.g. type 1 diabetes / bone marrow stem cell transplant ‘ blood cancers
21
Q
Explain how induced pluripotent stem cells are produced
A
- use adult somatic cells from patient
- add specific transcription factors which allow for genes associated with pluripotency to be expressed
- transcription factors attach to promoter regions of DNA stimulating or inhibiting transription
- culture cells to allow them to divide by mitosis
22
Q
Current research into the treatment of red-green colour blindness involves the use of induced pluripotent stem cells (iPS cells)
Suggest how iPS cells could correct red-green colour blindness. (2)
A
- (iPS cells) divide;
2. (iPS cells) develop/differentiate into (green sensitive) cones;
23
Q
Suggest how transcription factors can reprogramme cells to form iPS cells. (2)
A
1. Attach to gene / DNA / promoter region;
2. Stimulate / inhibit transcription / RNA polymerase;
24
Q
Evaluate the use of stem cells in treating human disorders
argue for - 4
A
for:
- can divide and differentiate into required healthy cells, so could relieve human suffering by saving lives and improving quality of life.
- embryos are often left over IVF and so would otherwise be destroyed.
- IPS cells unlikely to be rejected by patient’s immune system as made with patient’s own cells
- IPS cells can be made without destruction of embryo and adult can permission
25
Evaluate the use of stem cells in treating human disorders
- ethical issues with embryonic stem cells as obtaining them require destruction of an embryo and potential life ( embryo cannot consent)
- immune system could reject cells and immunosuppresant drugs are required.
- cells could divide out of control , leading to formation of tumours/cancer
26
what are transcription factors
- proteins which regulate (stimulate or inhibit) transcription of specific target genes in eukaryotes
- by binding to a specific DNA base sequence on a promoter region
27
Describe how transcription can be regulated using transcription factors
1. Transcription factors move from cytoplasm to nucleus
2. Bind to DNA at a specific DNA base sequence on a promoter region ( before/upstream of target gene)
3. this stimulates or inhibits transcription (production of mRNA) of target genes **by helping or preventing RNA polymerase binding.**
28
Explain how oestrogen affects transcription
- oestrogen is a lipid soluble steroid hormone so diffuses into cell across the phospholipid bilayer
- in cytoplasm, oestrogen binds to its receptor, an inactive transcription factor, forming an oestrogen-receptor complex.
- This changes the shape of the inactive transcription factor, forming an active transcription factor
- the complex difuses from cytoplasm into the nucleus
- then binds to a specific DN base sequence on the promoter region of a target gene
- stimulating transcription of target genes forming mRNA by helping RNA polymerase to bind
29
explain why oestrogen only affects target cells
- other cells do not have oestrogen receptors
30
Describe what is meant by epigenetics
- heritable changes in gene function / expression without changes to the base sequence of DNA
- caused by changes in the environment ( e.g. diet ,stress,toxins)
31
Describe what is meant by epigenome
- all chemical modification of DNA and histone proteins - methyl groups on DNA and acetyl groups on histones
32
Summarise the epigenetic control of gene expression in eukaryotes
- increased methylation of DNA :inhibits transcription
- decreased methylation of DNA: allows transcription
- increased acetylation of histones: allows transcription
- decreased acetylation of histones: inhibits transcription
33
Explain how methylation can inhibit transcription
1. Increased methylation of DNA: methyl groups added to cytosine bases in DNA
2. So nucleosomes (DNA wrapped around histone) pack more tightly together
3. Preventing transcription factors and RNA polymerase binding to promoter
34
Explain how acetylation can inhibit transcription
- decreased acetylation of histones increases positive charge of histones ( increases lysine +)
- so histones bind DNA ( negatively charged) more tightly
- preventing transcription factors and RNA polymerase bidning to promoters
35
Explain the relevance of epigenetics on disease development and treatment
- environmental factors (e.g. diet,stress,toxins) can lead to epigenetic changes
- these can stimulate/inhibit expression of certain genes that can lead to disease development
- **diagnostic tests** can be developed that detect the epigenetic changes before symptoms present
- **drugs can be developed** to reverse these epigenetic changes
36
What is RNA interference (RNAi)?
- a form of post-transcriptional modification which occurs in the cytoplasm.
- where siRNA, miRNA inhibis the translation of target mRNA.
- silencing gene expression.
37
Describe the regulation of translation by RNA interference
1. SiRNA/miRNA binds to a protein, forming an RNA induced silencing complex (RISC)
2. single-stranded miRNA/siRNA binds to target mRNA with a complementary base sequence
3. This leads to hydrolysis of mRNA into fragments which are then degraded / prevents ribosomes from binding
4. Reducing /preventing translation of target mRNA into protein
38
The scientists treated cells in a culture with small interfering RNA (siRNA). This siRNA causes RNA interference of expression of the CENP-W gene, which forms tubulin used in spindle fibres. The scientists took samples of cells at 0, 48 and 72 hours after adding the siRNA.
Suggest how the siRNA produced these results. (3)
1. siRNA binds to / destroys mRNA for CENP-W;
2. Prevents translation of CENP-W;
3. (After / as) CENP-W reduces so does tubulin production;
| Reject if siRNA binds to gene / DNA
Context is important, siRNA acts on
39
Describe how tumours and cancers form
| 8.2.3: gene expression and cancer
- mutations in DNA/genes controlling mitosis can lead to uncoontrolled cell division
- tumoour formed if this results in a mass of abnormal cells
- malignant: cancerous , can spread by metastasis
- benign: non-cancerous
40
Compare the main characteristics of benign and malignant tumours
**benign**:
- grows slowly/cells fivide less often
- cells are specialised
- normal regular nuclei
- **cannot spread to other parts of the body / metastasise; malignant:**
- grow faster
- unspecialised
- irregular /darker nuclei
- spread by metastasis: cells break off and spread to the other parts of the body
41
Describe the function of tumour supressor genes
- codes for proteins that
- inhibit / slow cell cycle (e.g. if DNA damage detected)
- or cause self-destruction (Apoptosis) of potential tumour cells (e.g. if damaged DNA can't be repaired)
42
Explain the role of tumour supressor genes in the development of tumours
-**A mutation in DNA base sequence** leads to the non-functional protein surpressor gene by leading to a change in amino acid sequence which changes protein tertiary structure
- **decreased histone acetylation or increased DNA methylation** prevents production of protein by preventing binding of RNA polymerase to promoter region,** inhibiting transcription**
- both lead to uncontrolled cell division
| - protein coded for by TG = non functional = uncontorlled division
43
Describe the function of proto oncongenes
- code for proteins that stimulate cell division
44
what are oncogenes?
- mutated /abnormally expressed form of the corresponding proto-oncogene
45
Explain the role of oncogenees in the development of tumours
| - through epigenetics and mutation
- **mutation** in DNA base sequence leads to an **overproduction** of protein or **permanently activated** protein by leading to change in amino acid sequence which chages protein tertiary structure.
**OR**
- **decreased DNA methylation **or **increased histone acetylation** - increases production of protein by stimulating the bidning of RNA polymerase to promoter region
- stimulating transcription leading to uncontrolled cell division
46
Suggest why tumours require mutations in both alleles of a tumour supressor gene but only one allele of an oncogene
- loss-of-function mutations that occur in tumor suppressor genes are recessive and so one mutation can still produce a protein to slow the cell cycle
- whereas one mutated oncogene allele can produce enough protein to lead to rapid/uncontrolled cell division as it is dominant
47
Explain how increased methylation **could lead to cancer** (3)
1. Methyl groups (could be) added to (both copies of) a tumour suppressor gene;
2. The transcription of tumour suppressor genes is inhibited;
3. Leading to uncontrolled cell division.
48
Explain the relevance of epigenetics in cancer treatment
- drugs could reverse epigentic changes that caused cancer, preventing uncontrolled cell division
- increasing DNA methylation or decreasing histone acetylation of oncogene to inhibit transcription/expression
- decreasing DNA methylation or increasing histone acetylation of tumour supressor gene to stimulate transcription / expression
49
Explain the role of increased oestrogen concentrations in the development of some ** breast cancers
| ** oestrogen-receptor positive
1. some breast cancer cells have oestrogn receptors , which are inactive transcription factors
2. if oestrogen concentration is increased , more oestrogen binds to oestrogen receptors, forming **more O-receptor complexes** which are active transcription factors
3. these bind to promoter regions of genes that code for proteins stimulating cell division
4. this increases transcription / expression of these genes increasnign the rate fo cell divison
50
Suggest how drugs that have a similar structure to oestrogen help treat oestrogen -receptor positive breast cancers
- drugs bind to oestrogen receptors ( inactive transcription factors , preventing binding of oestrgen
- so no fewer transcription factors bind to promoter regions of genes that stimulate the cell cycle
51
define:
- genome
- proteome
| 8.3
- genome: (All) the DNA/genes in a cell/organism/
- proteome: the full range of proteins that a cell can produce coded for by the cell's DNA / genome
52
What is genome sequencing and why is it important?
- identifying the DNA base sequence of an organism's genome
- so amino acid sequences of proteins can be determined.( proteome)
53
Explain how determining the genome of a pathoge could allow vaccines to be developed
- could identify the pathogen's proteome
- so could identify potential antigens ( proteins that stimulate an immune response) to use inn the vaccine
54
suggest some other potential applications of genome sequencing projects
- identification of genes / alleles associated with genetic diseases/ cancer
- new targeted drugs / gene therpy can be developed
- can screen patients , allowing early prevention / personalised medicine
- identification of species and evolutionary relationships
55
Explain why the genome cannot be directly translated into the proteome in complex organisms
- presence of non-coding DNA (e.g. introns within genes)
- presence of regulatory genes ( which regulate expression of other genes)
56
describe how sequencing methods have changed
- have become automated so are faster and more cost efffective
- they are continiously updated
57
What is recombinant DNA technology?
- transfer of DNA fragments from one organism or species to another
58
Explain why transferred DNA can be translated within cells of recipient transgenic organisms
1. genetic code is universal
2. transcription and translation mechanisms are universal
59
Describe the three examples of obtaining DNA fragments
| to be used in recombinant tech
1. using restriction enzymes
2. using reverse transcriptase
3. gene machine
60
Describe how DNA fragements can be produced using restriction enzymes
1. restriction enzymes cut DNA at specific base recognition sequences either side of the desired gene
2. shape of recognition site is complementary to active site
3. Many cut in a staggered fashion forming sticky ends / single stranded overhanging bases
61
Describe how DNA fragments can be produced from mRNA
- isolate mRNA from a cell that synthesises the protein coded for by the desired gene
- mix mRNA with DNA nucleotides and reverse transcriptase. RT uses mRNA as a template to synthesise a single strand of complementary DNA (cDNA)
- DNA polymerase can form a second strand of DNA using cDNA as a template
62
suggest two advantages of obtaining genes from mRNA rather than directly from the DNA removed from cells
- more mrna in cells making the protein then dna - so easily extracted
- in mRNA introns have been removed by splicing whereas DNA contains introns - so can be transcribed & translated by prokaryotes who can't remoove introns by splicing
63
Describe how fragments of DNA can be produced using a gene machine
- determine amino acid sequence of protein
- allows base sequence to be established
- these do not contain introns so can be transcribed and translated by prokaaryotes
- synthesises fragments of DNA quickly and accurately from scratch without need for a DNA template.
64
Name in vitro and in vivo techniques used to amplify DNA fragments
- in vitro ( outside a living organism): polymerase chain reaction
- in vivo (inside a living organism): culturing transformed host cells eg. bacteria
65
What is the mixture that is used in PCR?
- DNA fragments , DNA polymerase (e.g. taq polymerase) , primers and DNA nucleotides
66
Explain how DNA fragments can be amplified by PCR
1. **95°C**: this seperates DNA strands , breaking hydrogen bonds between bases
2. **55°C**: allows primers to bind to DNA fragment template strand by forming H bonds between complementary bases
3. **72°C**: nucleotides align next to complemenntary exposed bases. DNA polymerase joins adjacent DNA nucleotides , forming phosphodiester bonds
| mixture heated at x
## Footnote
this cycle is repeated. In every cycle, the amount of DNA doubles causing an exponential increase 2n
67
Explain the role of reverse transcriptase in RT-PCR. (1)
- Produces (c)DNA using (m)RNA;
- Accept: ‘converts’ (m)RNA to (c)DNA.
Reject: tRNA
68
69
Explain the role of primers in PCR
- Primers are short ,** single stranded** DNA fragments
- **complementary** to DNA base sequence **at start of desired gene to be copied**
- allowing DNA polymerase to bind to start synthesis
- two different primers are required as base sequences at ends are different
70
Suggest one reason why DNA replication eventually stops in PCR
- there are a limited number of primers and nucleotides which are eventually used up
71
what is a marker gene and what are they used for?
- marker genes code for fluorescent proteins which can be seen under UV light
- used to identify the successfully transformed bacteria
- those that have not taken up the desired gene can be destroyed and are not cultured
72
Explain why promoter and terminator regions are added to DNA fragments that are used to genetically modify organisms
***Promoter regions:***
- a sequence of bases that act as a binding site for RNA polymerase and transcription factors allowing transcription.
- Can be selected to ensure gene expression happens only in specific cell types
***Terminator regions:***
- Ensure transcription stops at the end of a gene, by stopping RNA polymerase
| TF : transcription facctors
73
What are the role of vectors in recombinant DNA technology?
- To transfer DNA into host cells / organisms eg. plasmids or viruses (bacteriophage).
74
Explain the role of **enzymes** in in vivo cloning
- Restriction endonucleases cut vector DNA
- The same enzyme is then used to cut the target gene out
- the vector/plasmid DNA &
DNA fragment have sticky ends that can join by complementary base pairing
- **DNA ligase** joins DNA fragments to vector DNA, **Forming phosphodiester bonds between adjacent nucleotides**
75
Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids. (4)
1. Restriction (endonuclease/enzyme) to cut plasmid/vector;
2. Ligase joins gene/DNA to plasmid/vector;
76
Describe how host cells are transformed using vectors
| the process what is added and why
- Plasmids enter bacterial cell membrane through following heat shock in a calcium ion solution
Or
- Viruses inject their DNA into cells which is then integrated into host DNA
77
Explain why marker genes are inserted into vectors
• To allow detection of genetically modified / transgenic cells / organisms
• If marker gene codes for antibiotic resistance, cells that survive antibiotic exposure = transformed
• If marker gene codes for fluorescent proteins, cells that fluoresce under UV light = transformed
• As not all cells / organisms will take up the vector and be transformed
78
Summarise the steps involved in amplifying DNA fragments in vivo
1. Isolate DNA fragment and Add promoter and terminator regions to the plasmid
2. Insert DNA fragments & marker genes into vectors (eg. plasmids) using restriction enzymes and ligases
3. Transform host cells (eg. bacteria) by inserting vectors
4. Detect genetically modified /transformed cells by identifying those containing the marker gene
5. Culture these transformed host cells, allowing them to divide and form clones
| tranform: refers to modification of the host cell / plasmid
79
Suggest how recombinant DNA tech can be useful in medicine
- GM bacteria produce human proteins (eg. insulin for type I diabetes) → more ethically acceptable than using animal proteins and less likely to cause allergic reactions
- GM animals / plants produce pharmaceuticals (pharming) → cheaper
• Gene therapy
80
Suggest how recombinant DNA technology can be useful in agriculture
- GM crops resistant to herbicides → only weeds killed when crop sprayed with herbicide
- GM crops resistant to insect attack → reduce use of insecticide
- GM crops with added nutritional value (eg. Golden rice has a precursor of vitamin A)
- GM animals with increased growth hormone production (eg. Salmon)
81
Suggest how recombinant DNA technology can be useful in industry
- GM bacteria produce enzymes used in industrial processes and food production
82
Describe gene therapy
- Introduction of new DNA into cells, often containing healthy / functional alleles
- To overcome effect of faulty / non-functional alleles in people with genetic disorders eg. cystic librosis
83
Suggest some issues associated with gene therapy
- effect is short lived as modifed cells (e.g. T cells) have a limited lifespan requires regular treatment
- immune response against genetically modiefied cells or viruses due to recognition of antigens
- long term effect not known: side effects can cause cancer
- DNA may be inserted into other genes , disrupting them - interfering with gene expression
84
Suggest why environmentalists and anti-globalisation activists might oppose recombinant DNA technology
- recombinant DNA may be transferred to other plants : potential herbicide resistant superweeds
- potential effects on food webs e.g. affect wild insects -> reduce biodiversity
- large biotech companies my control the technology and own patents
85
What are DNA probes?
- short single stranded pieces of DNA
- with a base sequence complementary to bases on part of a target allele/region
- usually labelled with a fluoresvent or radioactive tag for identification
86
Suggest why DNA probes are longer than just a few bases
- a sequence of a few bases would occur at many places throughout the genome
- longer sequences are only likely to occur in target alleles
87
What is DNA hybridisation?
- binding of a single stranded DNA probe to a complementary single strand of DNA
- forming hydrogen bonds/base pairs
88
Explain how gel electrophoresis can be used to seperate DNA fragments
1. DNA samples loaded into wells in a porous gel and covered in buffer solution ( which conducts eelctricity)
2. Electrical current passed thorugh - DNA is negatively charged so moves towards positive electrode
3. Shorter DNA fragments travel faster so travel further
89
what is gel electrophresis?
- a method used to seperate nucleic acid (DNA/RNA) fragments or proteins
- according to length/mass ( number of bases/amino acids) and charge (DNA is negatively charged due to phosphate groups and protein charge varies based on amino acid R groups)
| only length/mass in dna
90
Suggest two features of the structure of different proteins that enable them to be separated by gel electrophoresis. (2)
1. Mass/number of amino acids/polypeptides.
2. Charge;
3. R groups (differ);
## Footnote
Accept length of polypeptide/amino acid chain
Accept primary structure /sequence of amino acids.
Accept tertiary structure
91
How can one interpret data showing results of gel electrophoresis?
- run a standard with DNA fragments/proteins of known lengths under the same conditions
- compare to position of unknown DNA fragments/proteins to estimate their size
- shorter DNA fragments / proteins travel further / faster
92
Extract how genetic screening can be used to locate specific alleles of genes
1. extract DNA from cell sample and amplify by PCR
2. Cut DNA at specific base sequences ( either side of the target gene) using restriction enzymes to produce DNA fragments
3. Separate DNA fragments / alleles using gel electrophoresis
4. Transfer to a nylon membrane and treat to form single strands with exposed bases
5. Add labelled DNA probes which hybridise / bind with target alleles ( & wash to remove unbound probe)
6. To show bound probe, expose membrane to UV light if a fluorescently labelled probe was used or use autoradiography ( expose to X-ray film) if a radioactive probe was used.
93
Describe examples of the use of labelled DNA probes
- screening patients for heritable conditions (e.g. cystic fibrosis)
- screening patients for drug responses
- screening patients for health risks
94
Describe the role of a genetic counseller
1. Explain results of genetic screening including consequences of a disease
2. discuss treatments available for genetic conditiion
3. Discuss lifestyle choices/precautions that might reduce risk of a genetic condition developing
4. Explain probability of condition/alleles being passed onto offspring - enable patients to make informed decisions about having children
95
What is personalised medicine?
- medicine tailored to an individual's genotype / DNA
- increasing effectiveness of treatment e.g, by identifying to the particular mutation / allele causing cancer and treating it with tailored drugs.
96
Evaluate the screening of indidviduals for genetically determined conditions and drug responses
| For
- can enable people to make lifestyle choices to reduce chances of diseases developing
- allows people to make informed decisions about having their own biological children
- allows use of personalised medicisnes , increasing effectiveness of treatment
97
Evaluate the screening of indidviduals for genetically determined conditions and drug responses
| Against
- screening for incurable diseases or diseases that develop later in life (where nothing positivve can be done in response) may lead to depression.
- could lead to discrimination by insurance companies / employers
- may cause undue stress if patient does not develop the disease
98
what is genetic fingerprinting
- a laboratory technique that identifies a person by their DNA.
- It's used in forensics, medicine, and other scientific fields.
99
what are variable number tandem repeats (VNTRs)
- repeating sequences of nucleotides / bases
- found within non-coding sections of DNA at many sites throughout an organism's genome
100
why are VNTRs useful in genetic fingerprinting
- probability of two individuals having the same VNTRs is very low
- as an organism's genome contains many VNTRs and lengths at each loci differ between individuals
101
Explain how genetic fingerprinting can be used to analyse DNA fragments
1. Extract from sample (e.g.blood cells) and amplify by PCR
2. Cut DNA at specific base sequences/recognition sites using restriction enzymes
3. Separate VNTR fragments according to length using gel electrophoresis
4. Transfer to a nylon membrane and treat to form single strands with exposed bases
5. Add labelled DNA probes which hybridise . bind with complementary VNTRs & wash to remove unbound probe
6. to show bound probe , expose membrane to UV light if fluorescently labelled probe was used OR use autoradiography ( expose to X-ray film) if a radioactive probe was used.
102
Compare and contrast genetic fingerprinting with genetic screening
- both use PCR to amplify DNA sample
- Both use eelctrophoresis to seperate DNA fragments
- Both use labelled DA probes to visualise specific DNA fragments
- Genetic fingerprinting analyses VNTRs whereas geentic screening analyses specific alleles of a gene
103
Explain how genetic fingerprinting can be used to determine genetic relationships
- more closely related organisms have more similar VNTRs, so more similarities in genetic fingerprints
- paternity testing - father should share around 50% of VNTRs/ bads with child ( due to inheritance)
104
Explain how genetic fingerprinting can be used to fetermine genetic variability within a population
- differences in VNTRs arise from mutations, so more differences show greater diversity within a population
105
Explain the use of genetic fingerprinting in the fields of forensic science
- compare genetic fingerprinting of suspects to genetic fingerprint of DNA at a crime scene
- if many bands match , the suspect was likely present at the crime scene
106
Explain the use of genetic fingerprinting in the fields of medical diagnosis
- Some VNTR patterns are asssociated with an increased risk of certain genetic disorders
107
Explain the use of genetic fingerprinting in the fields of animal and plant breeding
- shows how closely related 2 individuals are , so that inbreeding can be avoided
- breed pairs with dissimilar genetic fingerprinting
