CAP 4 Flashcards
(54 cards)
1
Q
State three causes of genetic variation
A
- Mutation
- Crossing over
- Independent segregation / assortment (of homologous chromosomes)
- Random fusion of gametes / fertilisation / mating
2
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’
3
Q
What is a gene pool?
A
- All the alleles in a population;
4
Q
How do multiple alleles of a gene arise?
A
- mutations;
- which are different / at different positions in the gene;
5
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;
6
Q
What is meant by a recessive allele?
A
- Only expressed in the homozygote / not expressed in the heterozygote / not expressed if dominant present;1
7
Q
What does Hardy Weinberg’s equation predict
A
- The frequency/proportion of alleles (of a particular gene);
- Will stay 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;
8
Q
Define gene linkage
A
- (Genes/loci) on same chromosome;
9
Q
Define epistasis
A
- The allele of one gene affects or masks the expression of another in the phenotype;
10
Q
Describe why observed phenotypes don’t match expected values
A
- Fertilisation is random
- OR
- Fusion of gametes is random;
- Small/not-large population/sample;
- Selection advantage/disadvantage/lethal alleles;
11
Q
Define codominance
A
- Both alleles expressed in the phenotype;
12
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
13
Q
Rules for recessive alleles
A
- Unaffected parents can have an affected offspring (if they are Heterozygous)
14
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;
15
Q
Expected offspring phenotype ratios from heterozygous parents:
1. Monohybrid
2. Dihybrid
3. Epistasis
4. Autosomal linkage
A
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)
16
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;
17
Q
Explain how a single base substitution causes a change in the structure of a polypeptide
A
- Change in (sequence of) amino acid(s)/primary structure;
- Change in hydrogen/ionic/disulfide bonds;
- Alters tertiary/30 structure;
18
Q
Describe how DNA is replicated in a cell.
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.
19
Q
Why is the DNA heat to 95°C during PCR?
A
- Produce single stranded DNA
- Breaks WEAK hydrogen bonds between strands
20
Q
Why do you add primers during PCR?
A
- Attaches to / complementary to start of the gene / end of fragment;
- Replication of base sequence from here;
- Prevents strands annealing
21
Q
Explain why ‘base-pairs’ is a suitable unit for measuring the length of a piece of DNA
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;
22
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 (light);
- carcinogen / named carcinogen;
- mustard gas / phenols / tar (qualified);
23
Q
A deletion mutation occurs in gene 1.
Describe how a deletion mutation alters the structure of a gene.
A
- removal of one or more bases/nucleotide;
- frameshift/(from point of mutation) base sequence change;
24
Q
Describe the main stages in the copying, cutting and separation of the DNA.
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;
25
Describe the polymerase chain reaction.
* Heat DNA;
* Breaks hydrogen bonds/separates strands;
* Add primers;
* Add nucleotides;
* Cool;
* (to allow) binding of nucleotides/primers;
* DNA polymerase;
* Role of (DNA) polymerase;
* Repeat cycle many times;
26
Describe a plasmid.
* circular DNA;
* separate from main bacterial DNA;
* contains only a few genes;
27
Suggest one reason why DNA replication stops in the polymerase chain reaction
* Limited number of primers/nucleotides; /
Primers / nucleotides ‘used up’.
* DNA polymerase (eventually)denatures
28
Suggest why the restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once.
* 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)
29
Describe how the bacteria containing the insulin gene are used to obtain sufficient insulin for commercial use.
* use of fermenters;
* provides nutrients plus suitable conditions for optimum growth/named
* environmental factor;
* reproduction of bacteria;
* insulin accumulates and is extracted;
30
Explain what is meant by a vector.
* Carrier;
* DNA/gene; (context of foreign DNA)
* Into cell/other organism/host;
31
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;
32
mRNA may be described as a polymer. Explain why.
* Made up of many (similar) molecules/monomers/nucleotides/units
33
What is a DNA probe?
* (Short) single strand of DNA;
* Bases complementary (with DNA/allele/gene);
34
Name three techniques used by scientists to compare DNA sequences.
* Polymerase Chain Reaction
* DNA fingerprinting
* Gel electrophoresis
35
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;
36
Explain how cells produced from stem cells can have the same genes yet be of different types.
* {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
37
Describe the mechanism by which a signal protein causes the synthesis of mRNA.
* 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;
38
Explain how oestrogen enables RNA polymerase to transcribe its target gene.
* 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.
39
Compare the structure of dsRNA and DNA.
* 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;
40
Explain how the methylation of tumour suppressor genes can lead to cancer.
* Methylation prevents transcription of gene;
* Protein not produced that prevents cell division / causes cell death / apoptosis;
* No control of mitosis
41
Describe how alterations to tumour suppressor genes can lead to the development of tumours.
* (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;
42
Describe what is meant by a malignant tumour.
* mass of undifferentiated / unspecialised / totipotent cells;
* uncontrolled cell division;
* (not ‘repeated’)
* metastasis / (cells break off and) form new tumours /
* spread to other parts of body;
43
Describe how altered DNA may lead to cancer.
* (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;
44
Describe how alterations to tumour suppressor genes can lead to the development of tumours.
* (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;
45
Define epigenetics
* Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.
46
Describe what is meant by speciation (allopatric)
* Geographical isolation;
* Separate gene pools / no interbreeding (between populations);
* Variation due to mutation;
* Different environmental/abiotic/biotic conditions / selection pressures;
* Selection for different/advantageous, features/characteristics/mutation/ /allele;
* Differential reproductive success / (selected) organisms survive and reproduce;
* Leads to change in allelic frequencies;
* Cannot breed/mate to produce fertile offspring.
47
Describe what is meant by speciation (sympatric)
* NOT Geographical isolation;
* Leads to reproductive isolation
* Separate gene pools / no interbreeding (between populations);
* Selection for different/advantageous, features/characteristics/mutation/ /allele;
* Differential reproductive success / (selected) organisms survive and reproduce;
* Leads to change in allelic frequencies;
Cannot breed/mate to produce fertile offspring.
48
Describe how bacteria can become resistant to antibiotics
* Variation/variety;
* Mutation;
* Some plants have allele to survive/grow/live in high concentration of copper/polluted soils;
* (Differential) reproductive success / adapted organisms reproduce;
* Increase in frequency of allele;
* No interbreeding (with other populations) / separate gene pool / gene pool differs (from other populations);
49
Describe the process of succession
* (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;
50
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;
51
Describe systematic sampling
* 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;
52
Describe how you would determine the mean percentage cover for beach grass on a sand dune.
* 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;
53
Describe the mark, release, recapture technique
* 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
________________________________
Number marked in sample2;
54
Describe how you would determine how many quadrats to use when investigating a habitat
* 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;
