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A Level Biology AQA > 4. Genetic Information, Variation & Realtionships Between Organisms > Flashcards

4. Genetic Information, Variation & Realtionships Between Organisms Flashcards

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1
Q

Define : chromosome

A

A thread like structure made up of protein (eg: histones) & DNA by which hereditary information is physically passed from one generation to the next

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2
Q

Define : gene

A

Small section of DNA on a chromosome that controls a feature by coding for formation of one or more specific polypeptides or a functional RNA

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3
Q

Define : allele

A

A version of a gene with a different base sequence and therefore different code

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4
Q

What are the 2 main types of allele

A

Dominant (functioning)
Recessive (non-functional)

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5
Q

What are the 4 features of a genetic code

A

It’s a triplet code
It’s a degenerate code
It’s a non-overlapping code
It’s a universal code

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6
Q

Explain what is meant by degenerate code and why is it vital?

A

Means that most amino acids are coded for by more than 1 triplet
Vital to protect against point mutations (a change in a single base)

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7
Q

Why is the last base of 3 called the wobble base

A

It’s less likely to cause a harmful effect if mutated

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8
Q

Why is the genetic code being a non-overlapping code useful.

A

Each nucleotide is part of only one codon - mutation can only affect one codon

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9
Q

Compare and contrast dna in prokaryotes with dna in eukaryotes

A

In prokaryotic cells (eg. bacteria):
-DNA molecules are shorter, circular DNA and are not associated with protein molecules so do not have chromosomes
In eukaryotic cells:
-DNA molecules are larger, linear and associate with proteins (histones) so form chromosomes
-Enclosed in a nucleus

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10
Q

Describe the dna in mitochondria and chloroplasts

A

DNA is short and circular and not associated with proteins (histones)

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11
Q

Describe how DNA is packaged in eukaryotic chromosomes

A

A single length of dna is wrapped many times around lots of proteins called HISTONES to form NUCLEOSOMES.
These nucleosomes then coil up tightly to create CHROMATIN LOOPS which are wrapped around eachother to make a full CHROMOSOME
To protect the ends of the chromosomes, there are sections of dna called TELOMERES

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12
Q

Why can much of eukaryotic DNA be considered non-coding ?

A

Genes are only found on one strand of the DNA molecule. This is known as the sense strand
The other strand is known as the anti sense stand.
Not all the sense strand is coding (non coding regions are known as introns)
There are also base sequences between genes that are non-coding called minisatellites

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13
Q

What way does the sense strand run?

A

5’ to 3’

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14
Q

What is the anti sense strand also referred to as ?

A

Non-coding or template strand

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15
Q

What are minisatellites ?
What are they useful for?

A

Sections of repeated bases that aren’t transcribed
They vary enormously in number and size between individuals which allows for those non-coding regions to provide the basis of genetic fingerprinting for paternity tests and criminal investigations

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16
Q

What does it mean by the genetic code being universal ?

A

With no exceptions, each triplet codes for the same amino acid in all organisms.
Indirect evidence for evolution

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17
Q

How does the coded information on the dna in the nucleus get transferred to the cytoplasm where it is translates into proteins?

A

Sections of the dna code are transcribed onto a single stranded molecule called mRNA
(can leave through nuclear pores)

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18
Q

Define : codon

A

Refers to the sequence of three bases on mRNA that codes for a single amino acid

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19
Q

Define: genome

A

The complete set of genes in a cell, including those in mitochondria and/or chloroplasts

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20
Q

Define : proteome

A

The full range of proteins produced by the genome

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21
Q

Describe the structure of RNA

A

Forms a single strand
Each nucleotide is made up of :
The pentose sugar RIBOSE
One of the organic bases adenine, guanine, cytosine and uracil
A phosphate group

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22
Q

What are the two types of RNA important for protein synthesis

A

mRNA
tRNA

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23
Q

Describe the structure of mRNA

A

Long strand of nucleotides arranged in a single helix.
The base sequence of mRNA is determined by sequence of bases on the length of DNA in a process called transcription

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24
Q

Describe the structure of tRNA

A

Relatively small molecule that is made up of ~80 nucleotides.
It is a single stranded chain folded into a clover leaf shape, with one end of the chain extending beyond the other ( the part when are amino acid can attach )
At the opposite end of the tRNA molecule is a sequence of 3 other organic bases known as the anticodon

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25
Q

What happens at the anticodon ?

A

Anticodon is for complimentary base pairing with the codon of mRNA

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26
Q

Give a basic overview of the steps of polypeptide synthesis

A

DNA provides instructions in the form of a long sequence of bases
A complementary section of part of their sequence is made from a molecules called premRNA
The pre mRNA is spliced to produce mRNA
mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked forming a polypeptide

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27
Q

Give the full step by step process of transcription

A
  1. DNA helicase acts on a specific region of the DNA causing the 2 strands to separate& expose the nucleotide bases of that region
  2. The bases on the template strand (5’ to 3’) pair with the complementary free nucleotides
  3. RNA polymerase then moves along the strand and join nucleotides together to form a pre-mRNA molecule.
  4. As this occurs the DNA strands rejoin behind it (so only few bases are exposed at any one time)
  5. When the RNA polymerase reaches a particular sequence of bases recognised as the ‘stop’ codon, it detaches and production of pre-mRNA is complete
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28
Q

What way does the non sense / template strand run?

A

3’ to 5’

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29
Q

In which cells does splicing of pre-mRNA occur and why?

A

Eukaryotic cells !
In prokaryotic cells, transcription results directly in the production of mRNA whereas in eukaryotes transcription results in pre-mRNA because only DNA in eukaryotic cells have non-coding regions (introns) within a gene.

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30
Q

How does the splicing of pre-mRNA work?

A

The DNA of a gene in eukaryotic cells is made from sections called exons and sections called introns
The introns would prevent the synthesis of a polypeptide so they are removed by restriction endonucleases
The functional exons are rejoined by the enzyme ligase
Forms mRNA

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31
Q

What happens to the mRNA between when it’s formed in the nucleus and when it is ready for translation ?

A

mRNA molecules are too big to diffuse out of the nucleus and so they leave through nuclear pores
mRNA is attracted to ribosomes, it attaches and is ready for translation

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32
Q

Give the full step by step process of translation

A
  1. A ribosome attaches to starting codon at one end of the mRNA molecule
  2. The tRNA molecule with the complimentary anticodon sequence pairs with the codon on the mRNA. Also carries a specific amino acid
  3. Ribosome moves along the mRNA bringing together 2 tRNA molecules at any one time each pairing with the 2 corresponding codons on the mRNA
  4. The 2 amino acids on the tRNA are joined by a peptide bond using an enzyme and ATP
  5. Ribosome continues to next codon on the mRNA linking the amino acids at it goes
  6. As this happens the tRNA is released from its amino acids
    (Process continues - up to 15 amino acids added each second)
    (Up to 50 ribosomes can pass immediately behind the first so many identical polypeptides can be assembled simultaneously)
  7. Synthesis continues until ribosome meets a stop codon - polypeptide is complete
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33
Q

Explain how genes effectively control the activity of the cell

A

DNA sequence of triplets makes up a gene —-> sequence of codons on mRNA —-> order in which the tRNA molecules line up —-> sequence of amino acids in polypeptide.
Mean that gene precisely determine which protein a cell manufactures and because many of these proteins are enzymes, genes effectively control the activity of the cell

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34
Q

Define : splicing

A

Removal of introns and rejoining of exons

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35
Q

Define : exons

A

Base sequence that Code for a polypeptide (primary structure)

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36
Q

Define : introns

A

Sections of non-sense DNA that don’t code for proteins

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37
Q

Define : anticodon

A

Sequence of 3 adjacent nucleotides on a molecule of tRNA that is complementary to a particular codon on a molecule of mRNA

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38
Q

Compare and contrast semi conservative replication and transcription

A

Both use DNA helicase
Transcription copies one strand, semi conservative replication reads 2 strands
Transcription uses RNA polymerase, semi conservative replication uses DNA polymerase
Semi conservative replication uses more checking mechanisms (eg. Integrase )

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39
Q

Why is RNA being single stranded significant

A

Due to it being single stranded it is more chemically unstable- polypeptide synthesis will not continue indefinitely

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40
Q

Define : mutation

A

Any change to the quantity or base sequence of the DNA of an organism

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41
Q

Where do mutations occur ?

A

Most mutations occurs in somatic (body) cells & are not passed on
Only mutations that occur during the formation of gametes may be inherited

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42
Q

What are gene mutations

A

Any change to one or more of the nucleotide bases/sequence.
They can arise spontaneously during DNA replication and include base substitution & deletion

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43
Q

What is base substitution

A

The type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base

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44
Q

What is the effect of base substitution

A

The substitution of a base = change to the codon which results in production of a different amino acid
The significance of the change of one amino acid in the polypeptide chain will, depend on the precise role of the original amino acid

However due to the degenerate nature of the genetic code, the effect of the mutation is different if the new codon codes for the same amino acid as before = same polypeptide chain will form (mutation will have no effect )

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45
Q

What is base deletion

A

Arises when a nucleotide is lost form the normal DNA sequence (consequences can be considerable)

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46
Q

What is the common result of a base deletion

A

Frame shift occurs
Change in primary structure due to different amino acid sequence will in turn alter the tertiary structure. Protein is unlikely to function properly because the sequence of bases in the DNA is read in units of 3 bases.
Ie. If one base is deleted, bases will be shift one to the left and will be read differently

47
Q

What are chromosome mutations

A

Changes in the structure or number of whole chromosomes
They can arise spontaneously and can take 2 forms:
- Changes in whole sets of chromosomes
- Changes in the number of individual chromosomes

48
Q

What is the effect of changes in whole sets of chromosomes and how does it occur?

A

Occurs when organisms have 3 or more sets of chromosomes rather than the usual 2
This condition is called POLYPLOIDY and occurs mostly in plants

49
Q

What is the effect of changes in the number of individual chromosomes and how does it occur?

A

Sometimes individual homologous pairs of chromosomes fail to separate during meiosis
This is known as NON-DISJUNCTION and usually results in a gamete having 1 more / 1 fewer chromosome
( Example in humans is Down’s syndrome )

50
Q

What is a mutagen

A

Any agent which induces a mutation
Eg.
EM radiation: UV light, X-rays, Gamma rays
Chemicals: benzene, caffeine, pesticides

51
Q

What does meiosis produce

A

4 haploid daughter cells

52
Q

What does mitosis produce

A

2 diploid daughter cells

53
Q

What is the importance of meiosis

A

Sexual reproduction ( cells produced by meiosis are destined to become reproductive cells/gametes)
When 2 gametes fuse - halves to produce haploid cells (without this offspring would have twice the number of normal chromosomes

54
Q

Give a basic overview of the result of the first and second meiotic divisons

A

1st division : homologous pairs have been separated with one chromosome from each pair going into one of two daughter cells
2nd division : chromatids move apart - four cells are formed

55
Q

What is the locus

A

Position of a gene on a chromosome/DNA molecule

56
Q

What are homologous chromosomes

A

A pair of chromosomes, one maternal & one paternal, that have the same gene loci

A homologous pair is always 2 chromosomes that carry the same genes but not necessarily the same alleles of the genes

57
Q

How does independent segregation of homologous chromosomes occur

A

During meiosis 1 homologous chromosome pairs line up in the centre in a RANDOM arrangement
One of each pair will pass to each daughter cell - which one depends on how they are lined up and since it is random it is down to chance

58
Q

What is recombination by crossing over (meiosis)

A

After the homologous chromosomes have lined up at the equator of the cell….
CROSSING OVER - The chromatids of each pair become twisted around eachother
-During this, tensions are created & portions of the chromatids break off
RECOMBINATION - These broken portions might then rejoin with the chromatids of its homologous partner (usually equivalent portions are exchanged)

59
Q

What does it mean if recombination by crossing over doesn’t occur (meiosis)

A

Only 2 different cell types will be produced instead of the usual 4.
Therefore crossing over increases genetic diversity

60
Q

What is the calculation for the number of possible combinations of chromosomes for each daughter cell?

A

2^n
n= number of pairs of homologous chromosomes

61
Q

What is the calculation to predict the number of different combinations of chromosomes in the offspring produced ?

A

(2^n)^2
n= number of pairs of homologous chromosomes

62
Q

Why are the calculations to predict the possible chromosome combinations following meiosis not a good prediction

A

These calculations are based on the presumption that the chromosomes will stay in tact during meiosis however due to crossing over and recombination, the number of possible chromosome combinations in gametes would be increased

63
Q

What is genetic diversity

A

Differences in DNA/base sequences/alleles in a gene pool

64
Q

Define allele frequency

A

How often a particular allele occurs within a population

65
Q

Explain how genetic diversity can be decreased by natural selection

A
  • Within a gene pool of a species, random mutation of alleles result in a new allele of a gene (in most cases harmful)
  • however in certain environments the new allele might be advantageous
  • these individuals with this allele will be better adapted and therefore more likely to survive
  • they will be more likely to obtain available resources and so grow more rapidly and live longer
  • they reproduce and pass the advantageous allele on
  • the offspring with the advantageous allele are more likely to survive & reproduce successfully
  • over many generations the number of individuals with this allele will increase at the expense of the ‘less advantageous alleles’
  • over time the frequency of the advantegous allele increases as the other decreases
66
Q

What does directional selection involve ?

A

Favours individuals whose phenotypes fall on the left or right of the mean population.
This results in changes to the characteristics of the population (phenotypes at one extreme of the population being selected for and the other being selected against)

67
Q

What does stabilising selection involve

A

Selection that favours individuals with phenotypes closest to the mean (due to environmental conditions remaining stable)
This results in preserving characteristics of a population (individual with phenotypes at the extremes are less likely to pass on their alleles and so tend to eliminate these phenotypes)

68
Q

Give an example of stabilising selection within a population

A

Human birth weights against infant mortality.
When birth weight is outside the range 2.5-4kg there is a much greater risk of mortality

69
Q

Give an example of directional selection

A

Development of a population with resistance to an antibiotic

70
Q

What are the 3 types of adaptations that result in making a species better adapted to their environment

A

Anatomical- eg. Shorter ears in artic foxes compared to foxes
Physiological - eg. Oxidising of fat rather than carbs in kangaroos to produce additional water in desert conditions
Behavioural - eg. autumn migration of swallows

71
Q

What is a species ?

A

Individuals who are capable of breeding to produce living, fertile offspring

72
Q

What is the binomial system

A

Way organisms are named and identified (2 names)

73
Q

What helps members of a species recognise other members of the same species ?

A

They have similar or same genes and therefore resemble each other physically and biochemically
The ability to display a behaviour is genetically determined so similar behaviour helps

74
Q

What do courtship behaviours enable in order to ensure mating is successful and that the offspring have the maximum chance of survival ?

A
  • recognise members of their own species
  • identify a mate that is capable of breeding
  • form a pair bond
  • sychronise mating
  • become able to breed
75
Q

Why do individuals of a species need to be able to recognise members of their own species ?

A

Ensures that mating only takes place between members of the same species because…
only members of the same species can produce FERTILE offspring

76
Q

Why do individuals of a species need to be able to identify a mate that is capable of breeding ?

A

Because both partners need to be sexually mature, fertile and receptive to mate

77
Q

Why do individuals of a species need to be able to form a pair bond?

A

Will lead to successful mating and raising of offspring

78
Q

Why do individuals of a species need to synchronise mating

A

So that mating takes place when there is the maximum probability of the sperm and egg meeting

79
Q

Why is courtship behaviour used by males ?

A

To determine whether a female is at the receptive stage.
If she responds with the appropriate behavioural response, courtship continues and is likely to result in the production of offspring.
If she isn’t receptive she will exhibit a different pattern of behaviour and the male turns his attentions elsewhere

80
Q

What is the difference between classification and taxonomy

A

Classification is the grouping of organisms whereas the theory and practice of biological classification is known as taxonomy

81
Q

What are the 2 main types of biological classification ?

A

Artificial classification
Phylogenetic classification

82
Q

What is the role of artificial classification

A

Divides organisms according to differences that are useful at the time eg. colour, size, number of legs, leaf shape
(Described as analogous characteristics - same function but don’t have the same evolutionary origins)

83
Q

What is phylogenetic classification?

A

Based upon the evolutionary relationships between organisms and their ancestors
Classifies species into groups using shared features derived from their ancestors
Arranges the groups into a hierarchy, in which the groups are contained within larger composite groups with no overlap
(Relationships are partly based on homologous characteristics)

84
Q

What is meant by homologous characteristics ?

A

Homologous characteristics have similar evolutionary origins regardless of their functions in the adult of a species

85
Q

What are the three groups within a domain (highest taxonomic rank)

A

Bacteria
Archaea
Eukarya
(Each is divided into kingdoms)

86
Q

What are bacteria and what are their features

A

Group of single celled prokaryotes
Features:
- absence of membrane bound organelles
- unicellular although cells may occur in chains or clusters
- ribosomes are smaller (70s)
- cell walls are made of murein
- single loop of DNA made up of nucleic acids but no histones

87
Q

What are archaea and their features?

A

Group of single celled prokaryotes that were originally classified as bacteria
Differ from bacteria because :
- their genes and protein synthesis are more similar to eukaryotes
- their membranes contain fatty acid chains attached to glycerol by ether linkages
- no murein in cell walls
- they have a more complex form of RNA

88
Q

What are eukarya and their features ?

A

Group of organisms made up of one or more eukaryotic cells
Features:
- cells possess membrane bound organelles
- their membranes contain fatty acid chains attached to glycerol by ester linkages
- not all possess a cell wall but where they do they don’t contain murein
- ribosomes are larger (80s) than in bacteria and archaea

89
Q

Use the acronym to give the classification system

A

Kingdom
Phylum
Class
Order
Family
Genus
species

90
Q

Define phylogeny

A

The evolutionary relationship between organisms

91
Q

How are phylogenetic relationships of different species often represented?

A

Phylogenetic tree diagram (oldest species is base of tree, most recent ones are represented by the ends of the branches)

92
Q

Define biodiversity

A

The range and variety of genes, species and habitats within a particular region

93
Q

What are the 3 different components of biodiversity ?

A

Species diversity
Genetic diversity
Ecosystem diversity

94
Q

What does species diversity refer to ?

A

The number of different species and the number of individuals of each species within any one community

95
Q

What does ecosystem diversity refer to ?

A

The range of different habitats from a small local habitat to the whole of the Earth

96
Q

What is species richness?

A

A measure of species diversity
This is the number of different species in a particular area at any one given time (community)

97
Q

What is the equation for Simpsons Diversity index to investigate biodiversity

A

. N(N-1). N = total number of organisms of all species found
D= ————. n= total number of individuals found in the species you are
∑ n(n-1) interested in
D= diversity index

98
Q

The higher the species diversity index is..

A

The more stable an ecosystem usually is and the less likely it is to be affected by change.
ie. If there’s a drought, a community with a high species diversity index is much more likely to have at least some members survive & maintain a community
Usually results in a stable ecosystem in which communities are dominated by living organisms rather than climate

99
Q

What are the main overarching factors that have led to a reduction in biodiversity

A

Efforts to provide enough food for growing population at a low cost
Balance between conservation and farming

100
Q

What is the difference between argicultural ecosystems and natural ecosystems ?

A

Natural ecosystems develop over time to become complex communities with a high index of diversity
Agricultural ecosystems are controlled by humans

101
Q

How does farming contribute to the low species index of agricultural ecosystems ?

A

Farmers select species for particular qualities that make them more productive - therefore the number of species & the genetic variety of alleles they possess is reduced to the few that exhibit the desired features.
To be economic the number of these individuals needs to be large however, if most of the area is taken up by that one species, a smaller area is available for other species
These other species may not survive competition for space and resources (population of that species reduces)
In addition, pesticides are used to exclude these species

102
Q

What are some of the impacts of increased farming ?

A

Removal of hedgerows and grubbing out of woodland
Creation of monocultures
Filling in ponds and draining marsh and other wetland
Over grazing of land preventing regeneration

103
Q

Give examples of some of the management techniques that can be applied to increase species and habitat diversity

A

Maintain existing hedgerows at most beneficial height and shape (A-shape)
Plant edges over erecting fences as field boundaries
Maintain existing ponds and where possible create new ones
Plant native trees on land with low species diversity
Reduce use of pesticides (use biological control or GMOs instead)
Use crop rotation that includes nutrogen-fixing crop rather than fertilisers to improve soil fertility
Use intercropping rather than herbicides to control weeds and pests
Use organic fertilisers

104
Q

How was comparison of observable characteristics used to measure the genetic diversity ?
What are the limitations ?

A

Method was based on the fact that each observable characteristic is determined by a gene and the variety within a characteristic depends on the number and variety of alleles of that gene

Limitations :
A large number of characteristics are coded for by more than one gene (polygenic)
Differences in characteristics may be a result of different environmental conditions rather than different alleles

105
Q

What has using observable characteristics to measure genetic diversity been replaced by ?

A

Replaced by directly observing the DNA sequences themselves

106
Q

How can we use DNA base sequences to compare one species with another or to compare individuals in of the same species

A

Gene technology - DNA sequencing now routinely done by automatic machines and the data produced is analysed by computers
In these computerised systems each nucleotide base can be tagged using different fluorescent dyes. Sampling and sequencing DNA produces a pattern of coloured bands

107
Q

Describe how evolutionary relationships between species change overtime

A

When one species gives rise to another during evolution the DNA of the new species will initially be very similar to that of the species that gave rise to it
Due to mutations the sequences of nucleotide bases in the DNA will change
Overtime the new species will accumulate more differences in DNA

108
Q

Why can we use the base sequence of mRNA to measure DNA diversity

A

mRNA is coded for by DNA - base sequences on mRNA are complimentary

109
Q

How can we use the comparison of amino acid sequences in proteins to measure genetic diversity

A

The sequence of amino acids in proteins is determined by mRNA which is determined by DNA
The degree of similarity in the amino acid sequence of the same protein in 2 species will reflect how closely the two species are related
Comparison can be done by counting the number of similarities or differences in each sequence

110
Q

If one species differs from another it is called…

A

INTERspecific variation

111
Q

If members of the sAme species differ from eachother it is called…

A

INTRAspecific variation

112
Q

Name two ways in which meiosis produces genetic variation

A

Recombination by crossing over
Independent segregation

113
Q

Describe and explain the appearance of one of the chromosomes in the cell after replication

A

Chromosome formed of two sister chromatids because DNA replication has occurred.
Sister chromatids are held together by a centromere

114
Q

How can crossing over increase genetic variation ?

A

Crossing over involves exchanging sections of chromatids.
These sections have different alleles
New combinations of alleles formed

A Level Biology AQA (9 decks)

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