Cap 4 Flashcards
(79 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 ‘genes’/alleles’ ‘genetic material/code’ in a cell/organism/ person’
- ‘the total number of DNA bases in a cell/organism’
- the full base sequence of all the genetic material of an 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 within the same 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 phenotype) when homozygous
7
Q
Define dominant allele
A
Always expressed within the phenotype
8
Q
What does Hardy Weinberg’s equation predict? [3]
A
- The frequency of alleles (of a particular gene);
- Will stay constant from one generation to the next/over
generations / no genetic change over time; - (3 of the following) Providing no mutation/no selection / population large / population genetically isolated / mating at random / no migration;
9
Q
Define gene linkage
A
(Genes/loci) on same chromosome
10
Q
Define epistasis
A
The allele of one gene affects the expression of another in the phenotype;
11
Q
Define codominance
A
Both alleles (equally) 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
Male offspring (XY) are more likely than females (XX) 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;
14
Q
Expected offspring phenotype ratio from heterozygous parents:
Monohybrid
A
3 : 1
15
Q
Expected offspring phenotype ratio from heterozygous parents:
Dihybrid
A
9 : 3 : 3 : 1
16
Q
Expected offspring phenotype ratio from heterozygous parents:
Epistasis
A
9 : 4 : 3
or
15 : 1 (Ratio adds to 16 but is not 9 : 3 : 3 : 1)
or
9 : 7
17
Q
Expected offspring phenotype ratio from heterozygous parents:
Autosomal linkage
A
3:1 (if no crossing over)
(no other pattern other than 4 phenotypes with recombination of alleles)
18
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;
19
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 (of
polypeptide); - Change in (position of) hydrogen, ionic, disulfide bonds;
- Alters tertiary structure;
20
Q
Describe the process of crossing over and explain how it increases genetic diversity.
A
- Homologous pairs of chromosomes associate / form a bivalent;
- Chiasma(ta) form;
- (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
- Producing new combinations of alleles;
THIS IS ‘RARE’ = Unequal chance of recombinant alleles forming.
Less recombinant gametes form.
21
Q
Give two differences between mitosis and meiosis.
A
Mitosis given first
- One division, two divisions in meiosis;
- (Daughter) cells genetically identical, daughter cells genetically different in meiosis;
- Two cells produced, (usually) four cells produced in meiosis;
- Diploid to diploid/haploid to haploid, diploid to haploid in meiosis;
- Separation of homologous chromosomes only in meiosis;
- Crossing over only in meiosis;
- Independent segregation only in meiosis;
22
Q
A population of fruit flies contained 64% grey-bodied flies.
Body colour is controlled by gene G which has 2 alleles. G produces Grey and is dominant to g, which produces black.
Use the Hardy–Weinberg equation to calculate the percentage of flies heterozygous for gene G. [2]
A
48% [2]
q2=0.36 or (36/100)
so, q=0.6 and P=0.4
Therefore, 2 x 0.4 x 0.6 x [100] = 48%
2Pq [1]
0.48 [1]
23
Q
There were 850 fruit flies in one population. In this population, 510 fruit flies had the genotype WNWN, 255 had the genotype WNWV and 85 had the genotype WVWV.
Calculate the actual frequency of the allele WV. Do not use the Hardy-Weinberg equation in your calculation. [1]
A
0.25; [1]
WNWV = 1x 255 = 255
WNWV = 2 x 85 = 170
Therefore, (255 + 170) divided by (1700) = 0.25
Frequency is always shown as a proportion of 1.
24
Q
In a population, the frequency of the allele for tongue-rolling, T, is 0.4.
Use the Hardy-Weinberg equation to calculate the percentage of people in this population that are heterozygous for tongue-rolling.
A
48% [2]
P=0.4 so, q=0.6
2Pq [1]
0.48 [1]
= 2 x 0.4 x 0.6 x [100] = 48% [2]
25
In a species of snail, shell colour is controlled by a gene with three alleles. The shell may be brown, pink or yellow. The allele for brown, CB, is dominant to the other two alleles. The allele for pink, CP, is dominant to the allele for yellow, CY.
Give all the genotypes which would result in a brown-shelled snail.
CBCB, CBCP and CBCY;
26
What are the most common LIMITATIONS to a conclusion?
- No STATISTICAL TEST: Differences could be due to CHANCE
- Data is for only ONE (named) species
- Data only collected in a lab / In vitro
- Only tested on males / females. Observations may differ in
females / males
- Data is subjective
- Data only collected for ………….days / weeks / years
- Long term side effects are not known
- At no point is the ……… 100% effective.
27
Explain what is meant by the terms totipotent and pluripotent?
Totipotent cells can give rise to all cell types;
Pluripotent can only give some cell types;
28
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
29
Describe the mechanism by which a signal protein causes the synthesis of mRNA (6)
1) signal protein {binds to / joins to / interacts with / activates}
2) receptor on surface membrane;
3) messenger molecule moves from cytoplasm and enters nucleus;
4) {produces / activates} transcription factor;
5) binds to promoter region;
6)RNA polymerase transcribes target gene;
30
Explain how oestrogen enables RNA polymerase to transcribe its target gene (7)
1)Oestrogen is lipid soluble so diffuses through the 2)Oestrogen diffuses through the phospholipid cell
membrane;
3) attaches to ERα receptor;
4)ERα receptor changes shape / Tertiary structure;
5) ERα receptor leaves protein complex which inhibited it’s
action;
6) oestrogen receptor binds to promoter region;
7)enables RNA polymerase to transcribe target gene.
31
Compare the structure of dsRNA and DNA (8)
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;
32
Explain how the methylation of tumour suppressor genes can lead to cancer.
- Methylation prevents / inhibits transcription of (named)
gene;
- Protein not produced that prevents cell division / causes cell
death / apoptosis;
- No control of mitosis.
33
Describe what is meant by a malignant tumour.
- mass of undifferentiated / unspecialised / totipotent cells;
- uncontrolled cell division
- metastasis / (cells break off and) form new tumours / spread
to other parts of body;
34
Describe how altered DNA may lead to cancer (9)
1) (DNA altered by) mutation;
2) (mutation) changes base sequence;
3) of gene controlling cell growth / oncogene / that monitors
cell division;
4) of tumour suppressor gene;
5) change protein structure / non-functional protein / protein
not formed;
(6) tumour suppressor genes) produce proteins that inhibit
cell division;
7) mitosis;
8) uncontrolled / rapid / abnormal (cell division);
9) malignant tumour;
35
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;
36
Define epigenetics
Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.
37
Explain how a single base substitution causes a change in the structure of a polypeptide.
Do not include details of transcription and translation in your answer (3)
1.Change in (sequence of) amino acid(s)/primary structure;
2.Change in hydrogen & ionic & disulfide bonds;
3.Alters tertiary/30 structure;
38
There are different types of gene mutation.
Which statement describes incorrectly the effect of the mutation in an exon of a gene.
A substitution may not result in a change to the encoded amino acid.
An inversion will result in a change in the number of DNA bases.
A deletion will result in a frame shift.
An addition will result in a frame shift.
An inversion will result in a change in the number of DNA bases.
39
A type of malignant tumour cell divides every 8 hours.
Starting with one of these cells, how many tumour cells will be present after 4 weeks?
Assume none of these cells will die.
Give your answer in standard form.
1.9/1.93 × 1025
40
What name is used for the non-coding sections of a gene?
Introns
41
Explain why fragments of DNA from cancer cells may be present in blood plasma.
cancer cells die / break open releasing DNA;
42
Describe how alterations to tumour suppressor genes can lead to the development of tumours (4)
1. (Increased) methylation (of tumour suppressor genes);
Accept abnormal methylation or hypermethylation
2. Mutation (in tumour suppressor genes);
3. Tumour suppressor genes are not transcribed/expressed
OR
Amino acid sequence/primary structure altered;
4. (Results in) rapid/uncontrollable cell division;
43
The time required for a cell to complete the cell cycle was 4 hours 18 minutes.
Calculate the time required in minutes for this cell to multiply to produce eight cells.
774 minutes / 12 hours 54mins
44
Describe how DNA is replicated in a cell (7)
1) DNA strands separate / hydrogen bonds broken;
2) Parent strand acts as a template / copied / semi-
conservative replication;
3) Nucleotides line up by complementary base pairing; (
Adenine & Thymine etc)
4) Role of DNA polymerase: joins adjacent nucleotides on the
developing strand via condensation and formation of
phosphodiester bond;
5) 5’ to 3’ direction
6) Each new DNA molecule has 1 template and 1 new strand
7) Formed by semi-conservative replication.
45
Why is the DNA heat to 95°C during PCR?
Produce single stranded DNA
Breaks WEAK hydrogen bonds between strands
46
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
47
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;
48
Name one mutagenic agent.
- 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);
49
A deletion mutation occurs in gene 1.
Describe how a deletion mutation alters the structure of a gene.
- removal of one or more bases/nucleotide;
- frameshift/(from point of mutation) base sequence change;
50
Describe the main stages in the copying, cutting and separation of the DNA (fragments) (7)
1) heat DNA to 95°C / 90°C;
2) strands separate;
3) cool so that primers bind to DNA;
4) add DNA polymerase/nucleotides;
5) use of restriction enzymes to cut DNA at specific base sequence/ breaks phosphodiester bonds
6) use of electric current and agar/gel;
7) shorter fragments move further;
51
Describe the polymerase chain reaction (8)
* Heat DNA (95 degrees C);
* Breaks hydrogen bonds/separates strands;
* Add primers;
* Add nucleotides;
* Cool to (50 d.C);
* (to allow) binding of nucleotides/primers;
* Heat to 70-75 degrees C to activate Taq DNA polymerase;
* Role of (DNA) polymerase;
* Repeat cycle many times;
52
Describe a plasmid
circular DNA;
separate from main bacterial DNA;
contains only a few genes;
53
Suggest one reason why DNA replication stops in the polymerase chain reaction (2)
* Limited number of primers/nucleotides; /
Primers / nucleotides ‘used up’.
* DNA polymerase (eventually)denatures
54
Suggest why a restriction enzyme has cut the human DNA in many places but has cut the plasmid DNA only once (4)
* 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)
55
Describe how the bacteria containing the insulin gene are used to obtain sufficient insulin for commercial use (5)
* use of fermenters;
* provides nutrients plus suitable conditions for optimum growth/named
* environmental factor;
* reproduction of bacteria;
* insulin accumulates and is extracted;
56
Explain what is meant by a vector.
* Carrier;
* DNA/gene; (context of foreign DNA)
* Into cell/other organism/host;
57
Explain how modified plasmids are made by genetic engineering and how the use of markers enable bacteria containing these plasmids to be detected (9)
1. Isolate TARGET gene/DNA from another organism/mRNA from cell/organism;
2. using restriction endonuclease/restriction enzyme/reverse transcriptase to get DNA;
3. produce sticky ends;
4. use DNA ligase to join TARGET gene to plasmid;
5. also include marker gene; example of marker e.g. antibiotic resistance;
6. add plasmid to bacteria to grow (colonies);
1. (replica) plate onto medium where the marker gene is expressed;
7. bacteria/colonies not killed have antibiotic resistance gene and (probably) the TARGET gene;
8. bacteria/colonies expressing the marker gene have the TARGET gene as well;
58
mRNA may be described as a polymer. Explain why.
Made up of many (similar) molecules/monomers/nucleotides/units;
59
What is a DNA probe?
* (Short) single strand of DNA;
* Bases complementary (with DNA/allele/gene)
60
Name three techniques used by scientists to compare DNA sequences.
* Polymerase Chain Reaction
* DNA fingerprinting
* Gel electrophoresis
61
Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids (2)
1. Restriction (endonuclease/enzyme) to cut plasmid/vector;
2. Ligase joins gene/DNA to plasmid/vector;
62
Describe how enzymes could be used to insert the GH gene into a plasmid (2)
1.Restriction endonucleases/enzymes cuts plasmid;
OR
Restriction endonucleases/enzymes produces ‘sticky ends’;
Reject restriction enzymes cuts the gene.*
2. Ligase joins gene/DNA and plasmid
OR
Ligase joins ‘sticky ends’;
63
After obtaining copies of the HGH gene, the geneticist will attempt to insert them into plasmid vectors.
Describe how the geneticist would attempt to insert copies of the HGH gene into these plasmids (3)
1. Cut the plasmid with a restriction endonuclease;
. * Allow ‘add base sequences to blunt ends of plasmid and HGH gene’*
2. (So that) both have complementary / sticky ends;
3. (Mix together) and add ligase to join the complementary / sticky ends;
64
Suggest why the plasmids were injected into the eggs of silkworms, rather than into the silkworms (2)
* (If injected into egg), gene gets into all / most of cells of silkworm;
* So gets into cells that make silk.
65
Name the type of enzyme used to produce the cDNA.
Reverse transcriptase;
66
Describe what is meant by speciation (allopatric) = 8
* 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.
67
Describe what is meant by speciation (sympatric) = 6
* 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.
68
Describe how bacteria can become resistant to antibiotics (6)
* 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);
69
Describe the process of succession (7)
* (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;
70
Describe random sampling [estimation of population density] (4)
* Use a grid
* Use random numbers generator to determine random coordinates
* Count number of plants in a quadrat;
* Large sample
* Calculate mean num (per quadrat section);
* Mean number of plants per quadrat x number of quadrats
71
* Describe systematic sampling (2)
* Transect
* Place quadrats at regular intervals along the line;
* Count plants in quadrats
72
Describe how you would determine the mean percentage cover for beach grass on a sand dune (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 =
Num in sample1 × No in sample2
---------------------------------------------------
Number marked in sample 2
73
Describe how you would determine how many quadrats to use when investigating a habitat (4)
* Calculate 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;
74
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 (8)
1. Occur in Same habitat
2. Mutation causes diff flowering time
3. . Reproductive separation
4. . Different allele passed on
5. Gene pool remains separate
6. Change in allelic frequency
7. Natural selection (Disruptive selection) occurs
8. Eventually diff species
75
Changes in ecosystems can lead to speciation. A high concentration of copper in soil is toxic to most plants. In some areas where the soil is polluted with copper, populations of grasses are found to be growing. These populations of grass belong to a species also found growing on unpolluted soils. It has been suggested that a new species of grass may evolve on soil that has been polluted with copper.
Explain how this new species might evolve (6)
* Variation
* Caused by Mutation
* Some plants have allele to survive in high concentration of copper + polluted soils
* Differential reproductive success
* Increase in frequency of advantageous allele
* No interbreeding (with other populations) = separate gene pool
76
Changes in ecosystems can lead to speciation. In Southern California 10 000 years ago a number of interconnecting lakes contained a single species of pupfish. Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a number of different species of pupfish. Explain how these different species evolved (6)
* Geographical isolation = Allopractic speciation
* Separate gene pools = no interbreeding
* Variation due to mutation
* Different environmental conditions
* Selection for different/advantageous characteristics
* Differential reproductive success
* Leads to change in allele frequency;
* Occurs over a long period of time;
77
Describe how genetic fingerprinting is carried out (6)
1. DNA extracted from Sample
2. DNA cut using Restriction Endonuclease
3. Must leave VNRT's
4. Mixture put into wells on gel and electric current passed through
5. Immerse gel in alkaline solution
6. Radioative marker added
7. Areas with marker identified using X ray film
78
Fragment of DNA produced by (3)
* Converstion of mRNA to cDNA
* Use Restriction Endonucleuas to cut desired gene from DNA
* Create gene in gene machine
79
Outline method for in vivo gene cloning (7)
1. Cut desired gene
2. Using Restriction Endonuclease
3. Make artificial DNA with correct base sequence
4. Using DNA Polymerase
5. Cut Plasmid open using SAME restriction endonucleuase
6. Sticky ends attach using DNA ligase
7. Return Plasmid to cells
