4. Genetic Information, Variation & Realtionships Between Organisms Flashcards
(113 cards)
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
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
3
Q
Define : allele
A
A version of a gene with a different base sequence and therefore different code
4
Q
What are the 2 main types of allele
A
Dominant (functioning)
Recessive (non-functional)
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
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)
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
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
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
10
Q
Describe the dna in mitochondria and chloroplasts
A
DNA is short and circular and not associated with proteins (histones)
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
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
13
Q
What way does the sense strand run?
A
5’ to 3’
14
Q
What is the anti sense strand also referred to as ?
A
Non-coding or template strand
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
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
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)
18
Q
Define : codon
A
Refers to the sequence of three bases on mRNA that codes for a single amino acid
19
Q
Define: genome
A
The complete set of genes in a cell, including those in mitochondria and/or chloroplasts
20
Q
Define : proteome
A
The full range of proteins produced by the genome
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
22
Q
What are the two types of RNA important for protein synthesis
A
mRNA
tRNA
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
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
25
What happens at the anticodon ?
Anticodon is for complimentary base pairing with the codon of mRNA
26
Give a basic overview of the steps of polypeptide synthesis
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
27
Give the full step by step process of transcription
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
28
What way does the non sense / template strand run?
3’ to 5’
29
In which cells does splicing of pre-mRNA occur and why?
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.
30
How does the splicing of pre-mRNA work?
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**
31
What happens to the mRNA between when it’s formed in the nucleus and when it is ready for translation ?
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
32
Give the full step by step process of translation
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
33
Explain how genes effectively control the activity of the cell
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
34
Define : splicing
Removal of introns and rejoining of exons
35
Define : exons
Base sequence that Code for a polypeptide (primary structure)
36
Define : introns
Sections of non-sense DNA that don’t code for proteins
37
Define : anticodon
Sequence of 3 adjacent nucleotides on a molecule of tRNA that is complementary to a particular codon on a molecule of mRNA
38
Compare and contrast semi conservative replication and transcription
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 )
39
Why is RNA being single stranded significant
Due to it being single stranded it is more chemically unstable- polypeptide synthesis will not continue indefinitely
40
Define : mutation
Any change to the quantity or base sequence of the DNA of an organism
41
Where do mutations occur ?
Most mutations occurs in somatic (body) cells & are not passed on
Only mutations that occur during the formation of gametes may be inherited
42
What are gene mutations
Any change to one or more of the nucleotide bases/sequence.
They can arise spontaneously during DNA replication and include base substitution & deletion
43
What is base substitution
The type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
44
What is the effect of base substitution
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 )
45
What is base deletion
Arises when a nucleotide is lost form the normal DNA sequence (consequences can be considerable)
46
What is the common result of a base deletion
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
What are chromosome mutations
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
What is the effect of changes in whole sets of chromosomes and how does it occur?
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
What is the effect of changes in the number of individual chromosomes and how does it occur?
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
What is a mutagen
Any agent which induces a mutation
Eg.
EM radiation: UV light, X-rays, Gamma rays
Chemicals: benzene, caffeine, pesticides
51
What does meiosis produce
4 haploid daughter cells
52
What does mitosis produce
2 diploid daughter cells
53
What is the importance of meiosis
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
Give a basic overview of the result of the first and second meiotic divisons
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
What is the locus
Position of a gene on a chromosome/DNA molecule
56
What are homologous chromosomes
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
How does independent segregation of homologous chromosomes occur
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
What is recombination by crossing over (meiosis)
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
What does it mean if recombination by crossing over doesn’t occur (meiosis)
Only 2 different cell types will be produced instead of the usual 4.
Therefore crossing over increases genetic diversity
60
What is the calculation for the number of possible combinations of chromosomes for each daughter cell?
2^n
n= number of pairs of homologous chromosomes
61
What is the calculation to predict the number of different combinations of chromosomes in the offspring produced ?
(2^n)^2
n= number of pairs of homologous chromosomes
62
Why are the calculations to predict the possible chromosome combinations following meiosis not a good prediction
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
What is genetic diversity
Differences in DNA/base sequences/alleles in a gene pool
64
Define allele frequency
How often a particular allele occurs within a population
65
Explain how genetic diversity can be decreased by natural selection
- 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
What does directional selection involve ?
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
What does stabilising selection involve
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
Give an example of stabilising selection within a population
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
Give an example of directional selection
Development of a population with resistance to an antibiotic
70
What is a species ?
Individuals who are capable of breeding to produce living, fertile offspring
71
What is the binomial system
Way organisms are named and identified (2 names)
72
What helps members of a species recognise other members of the same species ?
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
73
What do courtship behaviours enable in order to ensure mating is successful and that the offspring have the maximum chance of survival ?
- recognise members of their own species
- identify a mate that is capable of breeding
- form a pair bond
- sychronise mating
- become able to breed
74
Why do individuals of a species need to be able to recognise members of their own species ?
Ensures that mating only takes place between members of the same species because…
only members of the same species can produce FERTILE offspring
75
Why do individuals of a species need to be able to identify a mate that is capable of breeding ?
Because both partners need to be sexually mature, fertile and receptive to mate
76
Why do individuals of a species need to be able to form a pair bond?
Will lead to successful mating and raising of offspring
77
Why do individuals of a species need to synchronise mating
So that mating takes place when there is the maximum probability of the sperm and egg meeting
78
Why is courtship behaviour used by males ?
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
79
What is the difference between classification and taxonomy
Classification is the grouping of organisms whereas the theory and practice of biological classification is known as taxonomy
80
What are the 2 main types of biological classification ?
Artificial classification
Phylogenetic classification
81
What is the role of artificial classification
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)
82
What is phylogenetic classification?
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)
83
What is meant by homologous characteristics ?
Homologous characteristics have similar evolutionary origins regardless of their functions in the adult of a species
84
What are the three groups within a domain (highest taxonomic rank)
Bacteria
Archaea
Eukarya
(Each is divided into kingdoms)
85
What are bacteria and what are their features
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
86
What are archaea and their features?
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
87
What are eukarya and their features ?
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
88
Use the acronym to give the classification system
Kingdom
Phylum
Class
Order
Family
*Genus*
*species*
89
Define phylogeny
The evolutionary relationship between organisms
90
How are phylogenetic relationships of different species often represented?
Phylogenetic tree diagram (oldest species is base of tree, most recent ones are represented by the ends of the branches)
91
Define biodiversity
The **range and variety** of **genes**, **species** and **habitats** within a particular region
92
What are the 3 different components of biodiversity ?
Species diversity
Genetic diversity
Ecosystem diversity
93
What does species diversity refer to ?
The number of different species **and** the number of individuals of each species within any one community
94
What does ecosystem diversity refer to ?
The range of different habitats from a small local habitat to the whole of the Earth
95
What is species richness?
A measure of species diversity
This is the number of different species in a particular area at any one given time (community)
96
What is the equation for Simpsons Diversity index to investigate biodiversity
. 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
97
The higher the species diversity index is..
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**
98
What are the main overarching factors that have led to a reduction in biodiversity
Efforts to provide enough food for growing population at a low cost
Balance between conservation and farming
99
What is the difference between argicultural ecosystems and natural ecosystems ?
Natural ecosystems develop over time to become complex communities with a high index of diversity
Agricultural ecosystems are controlled by humans
100
How does farming contribute to the low species index of agricultural ecosystems ?
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
101
What are some of the impacts of increased farming ?
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
102
Give examples of some of the management techniques that can be applied to increase species and habitat diversity
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
103
How was comparison of observable characteristics used to measure the genetic diversity ?
What are the limitations ?
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
104
What has using observable characteristics to measure genetic diversity been replaced by ?
Replaced by directly observing the DNA sequences themselves
105
How can we use DNA base sequences to compare one species with another or to compare individuals in of the same species
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
106
Describe how evolutionary relationships between species change overtime
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
107
Why can we use the base sequence of mRNA to measure DNA diversity
mRNA is coded for by DNA - base sequences on mRNA are complimentary
108
How can we use the comparison of amino acid sequences in proteins to measure genetic diversity
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
109
If one species differs from another it is called…
INTERspecific variation
110
If members of the s**A**me species differ from eachother it is called…
INTRAspecific variation
111
Name two ways in which meiosis produces genetic variation
Recombination by crossing over
Independent segregation
112
Describe and explain the appearance of one of the chromosomes in the cell after replication
Chromosome formed of two sister chromatids because DNA replication has occurred.
Sister chromatids are held together by a centromere
113
How can crossing over increase genetic variation ?
Crossing over involves exchanging sections of chromatids.
These sections have different alleles
New combinations of alleles formed
