Topic 4: Genetic information, variation and relationships between organisms Flashcards
(215 cards)
1
Q
`why is the genetic code described as universal
A
each triplet codes for the same amino acid in all organisms
2
Q
prokaryotic DNA
A
-short
-circular
-not associated with proteins
3
Q
eukaryotic DNA
A
-long
-linear
-associated with proteins called histones
-forms chromosomes
-mitochondria and chloroplasts contains prokaryotic DNA
4
Q
what do genes code for
A
A gene is a sequence of DNA bases that code for..:
-amino acid sequence of a polypeptide
-a functional RNA
5
Q
what is a gene
A
sequence of DNA bases that codes for a specific sequence of amino acids in a polypeptide
6
Q
triplet
A
A sequence of three DNA bases is called a triplet
A triplet codes for a specific amino acid. The genetic code is universal, non-overlapping and degenerate
7
Q
degenerate
A
most amino acids are coded for by more than one triplet
8
Q
non overlapping
A
each base in an exon is only read once
9
Q
universal
A
each triplet codes for the same amino acid in all organisms
10
Q
what is the fixed position which a gene occupies on a DNA molecule
A
locus/loci
11
Q
gene coding
A
A gene includes coding exons and non-coding introns sections of DNA
12
Q
How many bases code for a polypeptide of 24 amino acids
A
24 x 3 = 72
13
Q
Explain how a change in sequence of DNA bases could result in a non-functional enzyme
A
-change in sequence of amino acids
-change in bonding of tertiary structure so shape of active site is altered
-no enzyme substrate complexes can be formed
14
Q
Give two differences between the structure of mRNA and the structure of tRNA
A
-tRNA is clover shaped whereas mRNA is straight chained
-tRNA is only 80 bases (short) whereas mRNA is longer
-mRNA has no paired bases whereas tRNA does
15
Q
describe how mRNA is produced from an exposed template strand of DNA
A
-free RNA nucleotides form complimentary base pairs
-phosphodiester bonds form by action of RNA polymerase
16
Q
Describe how mRNA is formed by transcription in eukaryotes
A
-hydrogen bonds break between complimentary base pairs of DNA molecule by DNA helicase
-one DNA strand acts as a template
-free RNA nucleotides align by complimentary base pairings
-uracil replaced thymine
-RNA polymerase joins adjacent nucleotides by phosphodiester bonds
-pMRNA is spliced
17
Q
what is a codon
A
sequence of 3 bases on mRNA that codes for a single amino acid
18
Q
anticodon
A
a sequence of three nucleotides forming a unit of genetic code in a transfer RNA molecule, corresponding to a complementary codon in messenger RNA.
19
Q
true or false - in eukaryotic cells is only where pre-mRNA is formed
A
true
20
Q
introns
A
Introns –> sections of DNA that do not code for a polypeptide chain (protein)
21
Q
exons
A
sections of DNA that code for a polypeptide chain (protein)
22
Q
genome
A
-genome –> complete set of genes in an organism
23
Q
proteome
A
-proteome –> full range of proteins produced by the genome
24
Q
RNA
A
RNA –> single stranded, short, uracil replaces thymine, RNA polymerase, ribose pentose sugar
25
mRNA
mRNA --> contains genetic information from inside of the nucleus. DNA moves from cytoplasm to ribosomes for protein synthesis
26
tRNA
tRNA --> brings amino acids to mRNA to form proteins --> clover shape, short, only 80 bases long, amino acid attachment site, complimentary base pairs, anticodon
27
define transcription
-copy of DNA is made. This copy is known as messenger RNA which occurs in the nucleus of the cell
28
transcription
1) in nucleus, DNA helicase hydrolyses hydrogen bonds between complimentary base pairs to unwind double helix structure at target gene
2) free RNA nucleotides bind to complimentary base pairs on exposed template DNA strand
3) uracil replaces thymine
4) RNA polymerase catalyses formation of phosphodiester bonds between ribose sugar and phosphate groups of adjoining nucleotides to form sugar phosphate backbone
5) messenger RNA is formed and moves out of nucleus into cytoplasm. Pre-mRNA strand is spliced before leaving nucleus
6) DNA recoils as hydrogens bonds reform between template and coding strands
29
splicing of pre-mRNA
-removal of introns from mRNA to leave only exons
-functional exons joined together by splicing
-because most prokaryotic cells don’t have introns they don’t require splicing
30
define translation
-process where mRNaA is read and translated into a protein
-translation occurs on the ribosomes
-translation involves another type of RNA molecules known as tRNA
31
similarities between mRNA and tRNA
-both contain uracil
-both single stranded
-both contain codons (triplet bases)
32
differences between mRNA and tRNA
-mRNA is straight whereas tRNA is clover shaped
-mRNA is less stable than tRNA
-mRNA is larger than tRNA
-tRNA has an anticodon whereas mRNA doesn’t
-tRNA has an amino acid binding site whereas mRNA doesn’t
33
translation
1) mRNA leaves nucleus via a nuclear pore
2) mRNA attaches to a ribosome at start of codon
3) tRNA with an anticodon complimentary to start codon arrives at ribosome. TRNA molecule has specific amino acid attached to it
4) another tRNA molecule binds to second codon on mRNA. This brings another amino acid with it
5) Peptide bond forms between two amino acids
6) First tRNA molecule then leaves and process continues until stop codon is released. This is complimentary to the anticodon on a tRNA which does not have an associated amino acid. This signal the end of a polypeptide chain
34
define the term exon
sequence of DNA that codes for a polypeptide chain
35
explain how the proteome of a genetically modifed cell differs to one that is not genetically modified
-expression of a gene from different species
-new protein is formed
36
explain how can increase in rate of transcription of PIP1b gene will affect permeability of tobacco plant
-more aquaporin channels
-increase permability
37
describe the role of a ribosome in the production of a polypeptide
-mRNA attaches to ribosome at start codon
-2 codons
-allows tRNA iwth anticodons to bind
-specific sequence of amino acids with peptide bonds formed
38
true or false - pre-mrna has introns and mRNA doesnt
true
39
starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide
-mRNA attaches to ribosome
-codon on mRNA binds to anticodon on tRNA
-each tRNA brings a specific amino acid
-sequence of codons determines order of amino acids
-formation of peptide bonds
40
define species
organisms with similar features that are capable of breeding to produce living fertile offspring
41
naming organism
binomial systems
genus + species
42
signs of a recent common ancestor
-physical features, courtship behaviour, genome sequencing, amino acid sequencing, immune response
43
courtship behaviour (essential for successful mating)
-attracts members of the same species
-attracts member of the opposite sex
-indicated readiness to mate
-simulates making and release of gametes
-encouraged bond to raise young
44
start vs stop codon
start -> first 3 bases on DNA or mRNA
stop --> final 3 bases that do not code for an amino acid (mark end of polypeptide chain and cause ribosomes to detach)
45
how many amino acids does the genetic code, code for
20
46
what is a mutation
change in base sequence on a chromosome which results in the formation of a new allele
47
allele
different version of a gene
48
explain how a gene mutation could result in a new protein
-change in sequence of bases as a result of subsitution
-change in primary amino acid sequence
-change in tertiary structure of a protein
49
Explain why mutation 1 leads to the production of non-functional protein
-deletion of a base alters triplet/codon on mRNA molecule
-this change results in change in primary sequence of amino acids
-this change alters the hydrogen bonding in tertiary structure
50
define gene mutation and explain how a gene mutation can have no effect and a positive effect
-gene mutation is a change in base sequence of a chromosome molecule which results in the formation of a new allele
no effect --> when mutation occurs in an intron as it does not code for a polypeptide or if mutation occurs in recessive allele
positive effect --> change in properities of protein which leads to increased survival and reproductive success
51
define a mutagenic agent and give an example
-environmental factors which increase rate of mutation
e.g high energy radiation
52
what is a substitution mutation
replacement of a base by a different base in DNA
53
mutations
-a mutation is a change in the base sequence on a chromosome which results in the formation of a new allele
-mutations are random events which occur in S phase of cell cycle
-Some environmental factors can increase rate of mutation e,g toxins/radiation
-mutations don’t always change the protein formed e.g when it occurs in introns or bc the genetic code is degenerate bc same amino acid is being coded for
-some mutations result in a change in protein structure due to change in amino acid sequence which affects bonding in teritary structure
-mutations don’t always have negative effects e.g can increase an organisms chance of survival
54
causes of mutations
-occur spontaneously during interphase as DNA is replicated and it is the longest stage of the cell cycle
-high energy radiation or ionising energy can disrupt DNA e.g x-rays or UV light
-chemicals e.g nitrogen dioxide can disrupt DNA or interfere with transcription. Some chemicals in cigarette smoke can inactivate a tumor suppressor gene leading to cancer
55
natural mechanisms
-Natural mechanisms exist within cells to help identify and repair damaged to DNA but can become ineffective if rate of mutation increases above the normal rate
56
environmental factors which increase mutation rate
--> toxic chemicals e.g peroxides or bromine compounds
---> ionising radiation e.g gamma rays
--> high energy radiation e.g UV
--> some viruses – transfer of viral DNA into host DNA
57
what are the 2 types of mutation
-substiution
-deletion
58
substitution mutation
-wrong base is included in base sequence. May result in different amino acid being included in polypeptide chain
-however, if substitution results in a triplet that still codes for the same amino acid it may not change the sequence of amino acids at all bc the genetic code is degenerate
59
deletion mutation
-base is lost from the base sequence
-as a result the whole base sequence following the deleted base moves back one place (frame shift) which often has a significant effect on the encoded protein bc it can alter sequence of all codons following base deletion
-change of primary structure = fault enzymes/altered teritary structure
60
Describe how a gene is code for polypeptide
-nucleotide sequence in triplet determines primary sequence of amino acids
61
define non-coding base sequences and describe where it is positioned in the genome
-DNA that doesnt code for a polypeptide
-positioned between genes
62
similarites of DNA in prokaryotes and eukaryotes
-nucelotide structure is identical
-joined by phosphodiester bonds
63
suggest one way the structure of the chromosome could differ along its length to result in the stain binding to some more areas
-difference in base sequence
64
what is a homogolous pair of chromosomes
two chromosomes that carry the same genes
65
describe and explain the appearance of one of the chromosomes in cell X
-chromosomes are constructed from 2 chromatids
-due to cells undergoing replication these are held together by the centromere
66
describe what has happened during division 1 of meiosis
homologous pair of chromosomes have been separated into each daughter cell
67
identify one event that occurred during division 2 but not during division 1
separation of chromatids
68
name 2 ways in which meiosis produces genetic variation
-independent segregation of homologous chromosomes
-crossing over
69
name how two amino acids can differ from one another
have different R groups
70
why is the genetic code described as being universal
in all organisms the same triplet codes for the same amino acid
71
explain why homologous chromosomes carry the same genes but are not genetically identical
carry different alleles
72
give one way which meiosis allows the production of genetically different cells
crossing over (alleles exchanged between chromosomes)
73
meiosis
-In meiosis the daughter cells are haploid and genetically different (4 daughter cells)
-involves 2 nuclear divisions
-2 stages in meiosis
74
diploid vs haploid
Diploid = 2 cells = full sets of chromosomes
Haploid = 4 cells = half sets of chromosomes
75
define a tetrad
collection of 2 sets of homologous pairs (crossover)
76
prophase 1
Prophase 1 (variation):
-chromosomes condense and become visible
-crossing over = recombination of genetic material from chromatids
-provides genetic variation
77
metaphase 1
Metaphase 1 (random)
-chromosomes line up in homologous pairs at the equator
-chromosomes separate on the spindle fibers
-centromere with kinetochore
-microtubule attached to kinetochore
78
anaphase 1
Anaphase 1 (genetic crossover):
-independent segregation of chromosomes
-spindle fibres shorten
-pairs of homologous chromosomes split up
79
homologous pairs
two chromosomes with the same genes at the same loci
80
variation
Meiosis creates genetic variation through crossing over and random arrangement
81
first vs second division
First division:
-homologous chromosomes pair up and their chromatids wrap around eachother
-crossing over
-homologous pairs separate with one chromosome from each pair going into one of 2 daugther cells
Second division:
-chromatids move apart
-4 haploid daughter cells formed
82
name 2 biological molecules that can be codes for by a gene
-tRNA
-rRNA
83
kinetochore
a protein structure that is important for linking the chromosomes to the mitotic spindle and is assembled on the centromere.
84
explain how natural selection would produce a copper tolerant population in the mine waste
-a random mutation occured causing the grass to have higher copper tolerance
-natural selection will then occur as the grass with the copper tolerance is better adapted to the environment and is more likely to survive
-This means that the newly mutated grass is more likely to reproduce and pass on their advantageous alleles to their offpsring creating a new population of copper tolerant grass
-thusincreasing the frequency of copper tolerant alleles
85
define species
Species --> group of organisms that are able to interbreed to produce fertile offspring
86
define population
Population --> a group of organisms of the same species living in the same area at the same time
87
define genetic diversity
Genetic diversity --> total number of different alleles of genes in a population
The greater the genetic diversity the greater the likelihood that the same organisms will survive an environmental change
DNA results in genetic diversity
88
mutation = competitive
Most mutations are harmful but can lead to a competitive advantage in a population. This mutation increases the possessors evolutionary success
89
steps for natural selection
1) gene pool (wide variety of alleles)
2) Random mutation (new alleles)
3) Better adapted and better competitors
4) more likely to reproduce
5) Pass on successful advantageous alleles
6) survive and reproduce
7) Over time increased frequency of alleles
90
directional selection
-Normal distribution which shows where most common phenotype is
-shift to one extreme so one of the extreme phentoypes becomes most common
91
stabilising selection
-Shift to the middle = less extremes because extremes give a rise to disadvantages
-favour average
92
selection definition
Differences between the reproductive success of individuals affects allele frequency in populations
Selection --> process by which organisms that are better adapted to their environment tend to survive and breed
93
suggest one type of guppy behaviour that could be affected by the presence of brightly coloured stones
-mating habits change
94
describe a further investigation and null hypothesis
-include a control group with no coloured stones to compare
-there will be no difference....any difference will be due to chance
95
name the type of selection and explain why the frequency of alleles was affected
-directional selection
-extreme values are favoured
-random mutation becomes advantageous
96
the enzyme coded for one allele results in faster ctalysis than the other explain why
-different primary amino acid sequence
-difference tertiary structure so shape of active site changes
-formation of E-S complexes more likely
97
suggest why the scientist took his sample from the population at random
-so results are more likely to be reliable
98
stages of meiosis
The stages of meiosis can be split into two nuclear divisions, they are summarised below:
Meiosis 1 - homologous chromosomes pair up whereby crossing over at the chiasmata may take
place. The cell then divides whereby each daughter cell contains one chromosome from each
homologous pair.
Meiosis 2 - the chromatids of each chromosome are separated producing 4 haploid daughter
cells.
99
independent segregation of chromosomes
Independent assortment of chromosomes – there are various combinations of
chromosome arrangement. During meiosis 1 homologous chromosomes line up in pairs,
the arrangement of these pairs is random, meaning that the division into the daughter
cells is also random.
100
crossing over of chromatids
Crossing over of chromatids - When pairs of chromosomes line up they can exchange
some of their genetic material. Crossing over occurs when one chromosome may swap
places with the same part of its homologous pair leading to a different combination of
alleles on the gene.
101
directional vs stabilising selection
directional selection occurs when the environmental conditions change and the phenotypes best sutited to the new condition is more likely to survive whereas stabilising selection is when phenotypes with successful characteristics are preserved and genetic diversity is reduced
102
xerophytic adaptations
-spines for leaves
-extensive root network
-sunken stomata
-low stomatal density
-rolled leaves
-fleshy stem
103
types of adaptations
-Adaptations can be behavioural, physiological or anatomical
104
behavioral adaptation
Behavioural = changes in an organisms behaviour e.g closing of stomata when little water avaliable
105
physiological adaptation
Physiological = changes in the mechanisms within and an organism e.g plant mechanism to close the stomata or rolled leaves
106
anatomical adaptation
Anatomical = changes in the physical structure of an organism e.g spines for leaves
107
importance of courtship behaviour and what does it ensure
-courtship behaviour ensures successful production of fertile offspring
Importance of courtship behaviour:
-recognise/identify/attract organisms of the same species
-indicates sexual maturity and fertility
-formation of a paid bond
-stimulate mating and production of gametes
108
what is the importance of meiosis
halves chromosome number
109
the genetic does is described as being degenerate, What do this mean
one amino acid can be coded for by more than one triplet
110
what is a codon
triplet that codes for an amino acid
111
what is the role of RNA polymerase during transcription
join nucleotides together to form mRNA
112
mRNA can be converted to cDNA - what is the enzyme
reverse transcriptase
113
two molecules from which a ribosome is made
RNA and proteins
114
steps for meiosis
1) production of sister chromosomes/chromatids (replication)
2) chromosomes are found in homologous pairs and are arranged at equator of the cell
3) homologous chromosomes are separated and pulled to opposite parts of the cell (random)
4) meiosis 1 (2 genetically different cells)
5) sister chromatids separated again
6) Meiosis 2 = 4 haploid genetically different daughter cells
115
suggest why the frequency of ADf allele changed
-ADF allele has a selective advantage
-more likely to reproduce and pass on allele
-allele frequency increases
116
suggest and explain one reason why bacteria resistant to tetracycline was more common
-tetracyline used in higher doses
-resistance bacteria more likely to survive, reproduce and pass on allele for resistance
117
non-disjunction mutation
in meiosis, chromosomes not separated so dont form homologous pairs
118
apart from mutation select another way in which genetic variation within a species is increased
-random fertilisation
-produces new allele combination
119
Explain how the chromosome pair is halved during meiosis
one of each homologous pair goes to opposite poles of the cell
120
Describe the process of crossing over and how it increases genetic diversity
-homologus pairs of chromosomes associate
-alleles are exchanged on the chiasma producing new combinations of alleles
121
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation
-tRNA brings a specific amino acid
-anticodon on tRNA binds to codon on mRNA
-amino acids join by condensation reaction to form peptide bond
122
describe how a gene is code for the production of the polypeptide
-base sequence in triplet determines sequence of amino acid
123
calculate no. of chromosomes - meiosis
2 to the power of n
n = number of homologous chromosomes (same genes, different alleles)
124
crossing over
-chromatids twisted around eachother
-this puts tension on chromatids causing it to break off
-when it recombines crossing over happens
125
describe and explain 3 ways in which the scientist would ensure he used aseptic techniques to move each cube of agar onto a new agar plate
-flame instruments to sterilise and kill any contaminating microbes
-lift lid gently to prevent microbes getting in
-disinfect working surface to prevent contamination
126
give two differences between mitosis and meiosis
-mitosis produces 2 genetically identical diploid daughter cells whereas meiosis produces 4 genetically different haploid daughter cells
-mitosis has 1 cell division whereas meiosis has 2
127
describe how the process of meiosis results in the formation of haploid cells (4 marks)
-DNA replication
-2 divisions
-separation of homologous chromosomes in first division
-formation of 4 genetically different haploid daughter cells
128
suggest two reasons why it was important that they were of similar age
-to ensure they attract a mate
-so they have similar sexual maturity
129
explain the principles which biologists use to classify organisms into groups
-large groups divided into smaller groups based on evolutionary relationships
-members of each group have common features (homologous characteristics)
130
Give one feature of a hierarchy that is shown in the diagram
no overlap
131
what is meant by a hierarchy
-large groups divided into smaller groups (groups within groups) and no overlap
132
explain the role of independent segregation in meiosis
-provides genetic variation as it allows different combinations of maternal and paternal alleles
133
who developed the first classification system
Carl Linneaus
134
order of classification
-Domain --> Kingdom --> Phylum --> Class --> order --> family --> genus --> species
135
classification vs taxonomy
-Classification = group of organisms
-Taxonomy --> theory and practice of biological classification
136
two types of classification
phylogenetic and artificial
137
artificial classification
-Artificial classification = divides organisms according to features and differences
138
phylogenetic classification
-Phylogenetic classification = based on evolutionary relationships between organisms and their ancestors with no overlap.
Uses homologous characteristics = characteristics that have similar evolutionary origin
139
3 domains
3 domains --> bacteria, archaea, eukarya (classification based on DNA)
140
describe how organisms are grouped in a phylogenetic classification system
-heirachy of groups with no overlap
-groups according to evolutionary relationships
141
Explain how these sequences could provide evidence for different species
-different species would have different sequences of amino acids
-amino acid sequence is the result of DNA
142
state 3 comparisons of genetic diversity that the scientists could use
-base sequence of DNA
-base sequence of mRNA
-amino acid sequence of proteins
143
in this investigation what is meant by genetic diversity
the number of different alleles of each gene
144
suggest a reason why the diversity index for the lacewings is different between the two crops
more prey found on strawberries
145
bacteria
-single celled prokaryotes
-no membrane bound organelles such as nuclei
-cell walls made of murein
-circular DNA
146
archaea (differ to bacteria)
-genes and protein synthesis more similar to eukaryotes
-membranes contain ether linkages
-no murein in cell walls
-complex form of RNA polymerase
147
Eukarya
-membrane bound organelles
-membranes have ester linkages
-cell wall
-larger ribosomes
148
Eukaraya domain divided into 4 kingdoms
-Protoctistica
-Fungi
-plantae
-animalia
149
biodiversity
term used to describe variety in the living world
150
species diversity
can be measured by looking at the species richness and evenness
151
species richness and evenness
Species richness = total number of different species
Species evenness --> number of individuals of each species number of individuals of each
152
genetic diversity
Genetic diversity --> number of alleles within a species (variety of genes possessed)
153
ecosystem diversity
Ecosystem diversity --> range of different habitats
154
how to measure genetic diversity
-amino acid sequence of proteins encoded by DNA and mRNA
-the base sequence of DNA
-base sequence of mRNA
-frequency of measurable or observable characteristics
155
index of diversity
An index of diversity is a measurement that describes the relationship between the number of species present and how each species contributes to the total number of organisms that are present in that community
156
formula for index of diversity
n = total no. of organisms for a single species in the community
N = total no. of organisms in the community
Σ = sum of
The larger the number obtained, the higher the level of diversity
157
how to calculate index of diversity
To calculate:
Step 1: Calculate N(N-1) to find value A
Step 2: Calculate n(n-1) for each species
Step 3: Add these numbers together to find value B
Step 4: Divide value A by value B
158
give one advantage of calculating the index of diversity rather than just recording the number of species present
almost all of the sample could be the same species
159
using SD date from the table describe the differences in prokaryotic diversity found in the soil with these 2 farming methods
Define species richness and index of diversity in ur answe
-species richness = number of species in a community
index of diversity = relationship between number of species in a community and number of individuals in each species
-no SD overlap for species richness so it is significant
-index of diversity is not signifcant due to SD overlap
160
limitations of DNA sequencing
-non-coding DNA
-amino acid code is degenerate
161
suggest why in recent years has our knowledge about prokaryotic diversity in the soil increased
-DNA sequencing is now used
-observe more prokaryotes than before
162
Using a phylogenetic classification, all of these species have names that start with Apodemus. What information does this give
-they have the same genus
-they all share a common ancestor
163
common ancestor =
phylogenetic classification
164
describe how breeding experiments could determine whether the two populations are from the same species
-breed 2 mice from different populations together
-if produce fertile offspring = same species
165
why do humans and grasshoppers have similar percentages of each base in their DNA but are very different organisms
-different genes
-different triplet sequence
-different primary sequence of amino acids
166
why is DNA of virus different to that of other organisms
-no base pairing
-DNA single stranded
167
describe the primary structure of all proteins
-sequence of amino acids joined by peptide bonds
168
universal, non-overlapping, degenerate
universal = same triplet codes for the same amino acid
non-overlapping = each base is only part of one triplet
degenerate = more than one triplet codes for an amino acid
169
outline the similarties and differences between structure of chloroplasts and mitochondria
Similarities:
-ribosomes, circular DNA, double membrane
Differences:
-stroma vs matrix
-pigment vs no pigment
-starch grain vs no starch grain
170
explain how a gene codes for a protein
-base sequence in gene determines sequence of amino acids
-triplet codes for amino acid
171
define homologous chromosomes
-pairs of chromosomes with the same genes at the same loci
172
the method the scientists used resulted in them getting different scores for the same band. explain why
band width is not the same on both sides of the tail
173
explain how scientists could use this information to show that some variation in tail banding was genetic
-same family = look similar bc genetically similar bc from same parent
-random = more different
174
describe the cohesion tension theory
-water lost from leaf due to transpiration > evaporation through the stomata
-lowered water potention
-water pulled up xylem creating tension
-sticky H bonds = cohesion
-adhesion of water molecules to wall of the xylem
175
explain the importance of meioisis
-meiosis halves number of chromosomes (haploid cells)
-during fertilisation diploid number is resotred
-chromosome number remains constant
-introduces genetic variation
176
what happens to chromosomes during meiosis
-chromosomes condense
-associate in homologous pairs
-crossing over
-join to spindle fibres at equator of cell. Joined via centromere
-homologous chromosomes move to opposite poles
-chromatids seperated in 2nd division
177
meiosis and genetic variation
How it happens:
-crossing over
-independent segregation of chromosomes in meiosis I
-independent segregation of chromatids in meiosis II
Advantages:
-better adapted = increased survival
-reproduce and pass on genes
178
give one advantage of calculating the index of diversity rather than just recodring the number of species present
-takes account the number of individuals/population size
179
explain how differences in the primary structure of haemolgobin molecules can provide evidence of phylogenetic relationships between species
-mutations change base sequence
-causing change in amino acid sequence
-mutations build up over time
-more mutations = more differences in species that are closely related
-distantly related species have easier common ancestor
180
role of ribosomes and tRNA in translation
ribosomes = assemble amino acids to proteins by faciliating tRNA binding
tRNA = contains anticodon which is specific to codon on mRNA molecule
181
term used to describe ionising radiation
mutagenic agent
182
how does DNA replicate to produce sister chromatids
semi-conservative replication
183
why is standard deviation more useful than range
-shows spread of data around the mean
-reduces effect of anomalies
-indicate signifiance of results
184
dm3 =
1 L
185
structure of evaluate question
there is a positive correlation between
However data overlaps so correlation doesnt prove causation
no correlation coefficient to know signifiance
186
10^-7 is greater than 10^-8 true or false
true
187
minimum percentage decrease
distorted value - top end value given / distorted value
188
how to reduce uncertainity
-increase resolution of instrument used (mm instead of cm)
-take repeated readings
-incrase size
189
reading vs measurement
reading = single judgement e.g thermometer = +- 0.5
measurement = two judgements = ruler or stopwatch = +- 1.0 of the smallest division
190
why might his conclusion not be valid
only done on 1 type of cancer-> should be done on more types
dont know how much ECGC is in green tea
not all cancers are affected the same way
191
antibiotic resistance bacteria
-some bacteria have an allele for antibiotic resistance
-resistant bacteria survivie and reproduce
-high frequency of resistant allele in bacterial population
192
greater inhibition zone =
more effective antibiotic (more bacteria killed)
193
index of diversity
adundance of species + how many species
194
1 triplet =
1 amino acid
195
importance of enzymes
generate ATP/for respiration in cells
196
more red blood cells =
more haemoglobin
197
left ventricle = thicker wall =
stronger contractions
198
measure diversity between separate colonies =
frequency of base sequence alleles
199
suggest what further evidence would be needed to prove that the four populations of penguins are separate species
-breed individuals from one colony with another
-failure to produce fertile offpsirng = indicates different species
200
determine the number of gametes assuming there has been no corssing over
2^no of homologus pairs
e.g 6 chromosmes but 3 pairs
2^3
201
explain why comparing genes provides more evolutionary evidence than comparing proteins
more bases than amino acids (one triplet = 3 bases)
genetic code is also degenerate so more than one triplet may code for the same amino acid
202
suggest one reason why analysing genes coding for rRNA allows phylogenetic relationships to be studied between all cellular organisms
all cellular organisms have ribosomes
203
source of DNA from mammals
skin/bone etc
204
hunting =
reduce genetic diversity = fewer mammals alive = leads to inbreeding
205
reasons for low genetic diversity in populations
inbreeding
small population size
founder effect
206
suggest how the student would obtain data to give a more precise value of index of diversity
-take more samples and find the mean
-randomised method
207
too much herbicide =
toxic to plants
208
describe and explain the appereance of chromosomes in cell X
-chromosomes is formed of 2 chromatids
-bc of DNA replication = sister chromatids held together by centroemere
209
division 1
chromosomes in homologous pair
one of chromatids from each daughter cell
210
double helix structure
held by hydrogen bonds
+ DNA associated with histones = chromosomes
211
deletion =
removal of a base = missing amino acid = shorter polypeptide chain
212
why is the frequency of a genetic illness higher in smaller isolated islands
smaller islands = lower genetic diversity due to smaller gene pool
inbreeding occurs which also reduces the gene pool
213
why is it not possible to extrapolate data for the number of bird species recorded breeding each year
not a linear relationship
214
not a completley accurate measure of biodiversity
if the student hasnt recorded the index of diversity = number of indivudals in each species not shown
215
mark scheme process of translation
mRNA attaches to ribosome at start codon
tRNA anticodon binds to complementary codon on mRNA
tRNA brings a specific amino acid
Amino acids join via peptide bonds with the use of ATP
tRNA released
ribosome moves along mRNA to form the polypeptide
