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biology > CAP 4 > Flashcards

CAP 4 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
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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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’
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3
Q

What is a gene pool?

A
  • All the alleles in a population;
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4
Q

How do multiple alleles of a gene arise?

A
  • mutations;
  • which are different / at different positions in the gene;
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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;
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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
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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;
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8
Q

Define gene linkage

A
  • (Genes/loci) on same chromosome;
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9
Q

Define epistasis

A
  • The allele of one gene affects or masks the expression of another in the phenotype;
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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;
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11
Q

Define codominance

A
  • Both alleles expressed in the phenotype;
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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
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13
Q

Rules for recessive alleles

A
  • Unaffected parents can have an affected offspring (if they are Heterozygous)
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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;
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15
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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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;
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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;
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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.
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19
Q

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

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

Describe the polymerase chain reaction.

A
  • 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
Q

Describe a plasmid.

A
  • circular DNA;
  • separate from main bacterial DNA;
  • contains only a few genes;
27
Q

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

A
  • Limited number of primers/nucleotides; /
    Primers / nucleotides ‘used up’.
  • DNA polymerase (eventually)denatures
28
Q

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

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)
29
Q

Describe how the bacteria containing the insulin gene are used to obtain sufficient insulin for commercial use.

A
  • use of fermenters;
  • provides nutrients plus suitable conditions for optimum growth/named
  • environmental factor;
  • reproduction of bacteria;
  • insulin accumulates and is extracted;
30
Q

Explain what is meant by a vector.

A
  • Carrier;
  • DNA/gene; (context of foreign DNA)
  • Into cell/other organism/host;
31
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;
32
Q

mRNA may be described as a polymer. Explain why.

A
  • Made up of many (similar) molecules/monomers/nucleotides/units
33
Q

What is a DNA probe?

A
  • (Short) single strand of DNA;
  • Bases complementary (with DNA/allele/gene);
34
Q

Name three techniques used by scientists to compare DNA sequences.

A
  • Polymerase Chain Reaction
  • DNA fingerprinting
  • Gel electrophoresis
35
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;
36
Q

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

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
37
Q

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

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;
38
Q

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

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.
39
Q

Compare the structure of dsRNA and DNA.

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;
40
Q

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

A
  • Methylation prevents transcription of gene;
  • Protein not produced that prevents cell division / causes cell death / apoptosis;
  • No control of mitosis
41
Q

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

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;
42
Q

Describe what is meant by a malignant tumour.

A
  • 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
Q

Describe how altered DNA may lead to cancer.

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;
44
Q

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

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;
45
Q

Define epigenetics

A
  • Heritable phenotype changes (gene function) that do not involve alterations in the DNA sequence/mutation.
46
Q

Describe what is meant by speciation (allopatric)

A
  • 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
Q

Describe what is meant by speciation (sympatric)

A
  • 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
Q

Describe how bacteria can become resistant to antibiotics

A
  • 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
Q

Describe the process of succession

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;
50
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;
51
Q

Describe systematic sampling

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;
52
Q

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

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;
53
Q

Describe the mark, release, recapture technique

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
    ________________________________
    Number marked in sample2;
54
Q

Describe how you would determine how many quadrats to use when investigating a habitat

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;

biology (7 decks)

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