B9 Flashcards
(56 cards)
1
Q
mutation
A
any change in the quantity or the base sequence of the DNA of an organism
2
Q
gene mutation
A
any change to one or more nucleotide bases, or a change in the sequence of bases
3
Q
substitution of bases
–> why its harmful
A
type of gene mutation where a nucleotide in a DNA molecule is replaced by another nucleotide with a different base
- if this change in base sequence changes the amino acid coded for, the polypeptide will be different
- the significance of this difference will depend on the role of the original amino acid
- if it is important in forming bonds that determine the tertiary structure of the final protein, the substituted amino acid may not form the same bonds
e.g. an enzyme may have different shape active sires, no longer complementary to substrate, no enzyme-substrate complexes formed, so cannot catalyse reaction
4
Q
deletion of bases
A
when a nucleotide is lost from the normal DNA sequence
- usually the amino acid sequence of the polypeptide is entirely different and so the polypeptide cannot function
- this is because the sequence of bases in DNA is read in units of triplets
- one deleted nucleotide causes all triplets in a sequence to be read differently , because each has been shifted to the left by one base
5
Q
chromosome mutations
–> forms
A
changes to the structure or number of whole chromosomes
- changes in whole sets of chromosomes
- when organisms have 3 or more sets of chromosomes rather than the usual 2
–> POLYPLOIDY - changes in the number of individual chromosomes
- sometime individual homologous pairs of chromosomes fail to separate during meiosis
–> NON DISJUNCTION - results in a gamete having either one more or one fewer chromosomes - on fertilisation with a gamete that has the normal amount of chromosomes, the resultant offspring have more or fewer chromosomes in all their body cells
6
Q
hybridisation
A
combining the genes of different variations or species of organisms to produce a hybrid
sometimes this is followed by organisms that have additional complete sets of chromosomes
7
Q
how can polyploidy arise
A
- chromosomes do not separate into two distinct sets during meiosis
- gametes could them be produced that have both sets i.e. they are diploid rather than haploid
- if these fused with one another, the offspring could have four sets of chromosomes- tetraploid
- diploid + haploid = triploid - hybrids can be formed by combining sets of chromosomes from two different species
8
Q
when are hybrids not sterile
A
- if the hybrid has a chromosome number that is a multiple of the original chromosome number, a new fertile species cam rise because chromosomes have homologous partners so meiosis is possible
9
Q
how does cell division occur (2 ways)
A
- mitosis: produces two daughter cells with the same number of chromosomes as the parent cell and each other
- meiosis: usually produces 4 daughter cells, each with half the number of chromosomes as the parent cell
10
Q
what is the haploid number
A
- during meiosis, homologous pairs separate so that only one chromosome from each pair enters a daughter cell
–> in humans the haploid number = 23
11
Q
the process of meiosis
A
- involves 2 nuclear divisions that normally occur one after another
- meiosis 1
- homologous chromosomes pair up and their chromatids wrap around each other
- equivalent portions of these chromatids may be exchanged by CROSSING OVER
- by the end of this division, the homologous pairs have separated, with one chromosome from each pair going into one of the two daughter cells - meiosis 2
in the second mitotic division, the chromatids move apart
- at the end of meiosis 2, four cells have been formed
- in humans, each contain 23 chromosomes
12
Q
how does meiosis bring about genetic variation
A
- independent segregation of homologous chromosomes
- new combinations of maternal and paternal alleles by crossing over
13
Q
gene
A
a length of DNA that codes for a polypeptide and functional RNA
14
Q
locus
A
a position of a gene on a chromosome/ DNA molecule
15
Q
allele
A
one of the different forms of a particular gene
16
Q
homologous chromosomes
A
a pair of chromosomes, one maternal/ paternal, that have the same gene loci
17
Q
independent segregation of homologous chromosomes
A
- during meiosis 1, each chromosome lines up alongside its homologous partner
- in humans, 23 homologous pairs lying side by side
- the arrangement of these homologous chromosomes = RANDOM
- one of each pair will pass to each daughter cell
- which one of each pair goes into the daughter cell, and which one of any other pairs, depends on how the pairs are lined up in the parent cell.
- since the pairs are lined up at random, the combination of chromosomes of maternal and paternal origin that go into the daughter cells at meiosis 1 is also a matter of chance.
18
Q
variation from new genetic combinations
A
- each member of a homologous pair of chromosomes has exactly the same genes and therefore determines the same characteristics
- however, the alleles of these genes may differ
- the INDEPENDENT ASSORTMENT of these chromosomes therefore produces new genetic combinations,
19
Q
genetic recombination by crossing over
A
- during meiosis 1, each chromosome lines up alongside its homologous partner
- the chromatids of each chromosome become twisted around each other
- during this twisting process, tensions are created and portions of the chromatids break off
- these broken portions rejoin with the chromatids of the homologous partner
- in this way, new genetic combinations of maternal and paternal alleles are produced
- chromatids = produced with a different combination of alleles between non-sister chromatids
—> chiasma/ chiasmata form
20
Q
possible chromosome combinations following meiosis
A
- homologous pairs of chromosomes line up at the equator of a cell during meiosis 1
- either one of a pair can pass into each daughter cell - INDEPENDENT SEGREGATION
- number of possible combinations for each daughter cell = 2^n
- variety is further increased through the random pairing of male and female gametes
- where the gametes come from different parents, two different genetic complements with different alleles are combined –> more variety.
(2^n)^2 - these calculations are based on chromosomes staying intact throughout meiosis
- crossing over between chromatids during meiosis 1 exchanges sections of chromosomes between homologous pairs in recombination
21
Q
organisms of the same species differ in …
A
the combination of their alleles, not their genes
22
Q
genetic diversity
A
a measurement of variation in a population. the total number of different alleles for each gene present in a population
23
Q
population
A
a groups of individuals of the same species that live in the same place and can interbreed,
24
Q
how does genetic diversity enable natural selection
A
- the greater number of different alleles that all members of a species possesses i.e. the greater genetic diversity
–> the more likely that some individuals in a population will survive an environmental change - this is because of a wider range of alleles and therefore a wider range of characteristics
- this gives a greater probability that some individuals will possess a characteristic that suits it to the new environmental conditions
25
sources of variation
- mutations
- meiosis
--> independent segregation
--> crossing over
- random fusion of gametes
26
gene pool
total number of all alleles of all the genes present in a population at any given time
27
why are not all alleles of a population equally likely to be passed on to the next generation
- only certain individuals are reproductively successful and so pass on their alleles
- differences between the reproductive success of individuals affects allele frequency in populations
28
allele frequency
+ natural selection
allele frequency = how often an allele occurs in a population
- within any population of a species, there will be a gene pool containing a wide variety of alleles
- random mutation of alleles within this gene pool may result in a new allele of a gene, in most cases, will be harmful
- however, in certain environments, the new allele of a gene might give its possessor an advantage over other individuals in a population
- these individuals will be better adapted and therefore more likely to survive in their competition with others
- these individuals are more likely to grow more rapidly and live longer
- so they will have a better chance of breeding successfully and producing more offspring
- only those individuals that reproduce successfully will pass on their alleles to the next generation
- as these new individuals also have the new 'advantageous' allele, they are more likely to survive and reproduce successfully
- over many generations, the number of individuals with the new advantageous allele will increase
- over time, the frequency of the new 'advantageous' allele in the population increases and that of the non-advantageous allele decreases
what is 'advantageous' depends on the environmental conditions at the time
29
selection
the process by which organisms that are better adapted to their environment tend to survive and breed, while those that are less well adapted tend not to
30
directional selection
selection may favour individuals that vary in one direction from the mean of the population
--> this changes the characteristics of the population
- if the environmental conditions change, the phenotypes that are best suited to the new conditions are most likely to survive
- some individuals which fall either side of the mean will possess a phenotype more suited to the new conditions
- these individuals will be more likely to survive and breed
- over time, the mean will then move in the direction of these individuals and the individuals in the other direction will be selected against
31
stabilising selection
selection may favour average individuals
- this preserves the characteristics of the population
- if the environmental conditions remain stable, individuals with the phenotype closest to the mean are favoured
- stabilising selection eliminates the phenotypes at the extremes
32
polygenes
most characteristics are influenced by more than one gene- polygenes
- these types of characteristics are more influenced by the environment than one determined by a single gene
- the effect of the environment on polygenes produces individuals in a population that vary about the mean
- when you plot this variation on a graph, you get a normal distribution curve
33
disruptive selection
- favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population
- the opposite of stabilising selection
- favours extreme phenotypes at the expense of the intermediate phenotypes
- most important in bringing about evolutionary change
- occurs when an environmental factor, such as temperature, takes two or more distinct forms
34
how does natural selection result in species that are better adapted to the environment
anatomical: e.g. shorter ears, thicker fur
physiological: e.g. oxidising fat rather than carbohydrate to provide more water
behavioural: e.g. migration to avoid food shortage
35
biodiversity
the variety of life in the world or in a particular habitat/ ecosystem
36
ecosystem
consists of all the living (biotic) and non-living (abiotic) things that can be found in a certain area.
the living things within an ecosystem form a community
37
species diversity
the number of different species and the number of individuals of each species (abundance) within any one community
38
genetic diversity
the variety of genes possessed by the individuals that make up a population of a species
39
ecosystem diversity
the range of different habitats
40
species richness
the number of different species in a particular area at a given time (community)
41
species diversity and ecosystems
- biodiversity reflects how well an ecosystem is likely to function
- the higher the species diversity index, the more stable an ecosystem is and the less it is affected by change e.g. climate change
- if there is a drought, a community with a high species diversity index is much more likely to have at least one species able to tolerate drought than a community with a low species diversity index
- at least some members are therefore likely to survive the drought and maintain a community
- in extreme environments e.g. hot deserts, only a few species have the necessary adaptations to survive in harsh conditions
- the species diversity index is therefore normally low- communities = dominated by climatic factors rather than the organisms within the community
42
impact of agriculture on biodiversity + index of biodiversity
- farmers often select species for particular qualities that make them more productive
- as a result, the number of species and the genetic variety of alleles they possess is reduced to the few that exhibit the desired features
- to be economic, the number of individuals of these desirable species must be large
- any particular area can support a certain amount of biomass
- if most of the area is taken up by the one species that is considered desirable, there is a smaller area for other species
- these other species have to compete for what little space and resources are available
- pesticides are used to exclude these species because they compete for the light, mineral ions, water, and food required by the farmed species
- overall effect = reduction in species diversity
- the index of diversity = therefore low in agricultural ecosystems
43
effect of expanding human population on food production
- expanding human population --> produce food more intensley
- in the UK, food production has doubled over the past 40 years
- this has been achieved by the use of improved genetic varieties of plant and animal species, greater use of chemical fertilisers and pesticides, greater use of biotechnology and changes in farm practices
---> leading to larger farms and the conversion of land supporting natural communities into farmland
- main effect: diminishes the variety of habitats within ecosystems and so reduces biodiversity
44
practices that have directly removed habitats and reduced species diversity
+ those that have had a more indirect effect
- removal of hedgerows
- creating moncultures
- filling in ponds and draining marsh and other wetland
- over-grazing of land, preventing regeneration
- use of pesticides and inorganic fertilisers
- escape of effluent from silage stores and slurry tanks into water courses
- absence of crop rotation and lack of intercropping
45
conservation techniques
- maintaining hedgerows at the best height + shape
---> A- shape provides better habitats than rectangular
- plant hedges rather than use fences as field boundaries
- maintaining existing ponds + create new ones
- leave wet corners of fields rather than draining them
- plant native trees on land with a low species diversity rather than in species rich areas
- reduce use of pesticides- use biological control where possible or GM organisms resistant to pests
- use organic, not inorganic, fertilisers
- use crop rotation that includes a nitrogen-fixing crop, rather than fertilisers, to improve soil fertility
- use intercropping rather than herbicides to control weeds and other pests
- create natural meadows and use hay rather than grasses for silage
- leave the cutting of verges and field edges until after flowering and when seeds have dispersed
- introduce conservation headlands- areas at the edges of fields where pesticides are used restrictively so wild flowers and insects can breed
these practises will make food slightly more expensive to produce, and therefore, to encourage farmers, there are a number of financial incentives from the Department for Environment, Food and Rural Affaris and the EU
46
comparison of observable characteristics
- based on the fact that each observable characteristic is determined by a gene or genes (with environmental influences)
- the variety within a characteristic depends on the number and variety of alleles of that gene (+ environmental influences)
- using observable characteristics has limitations because a large number of them are coded for by more than one gene- polygenic
- this means that they are not discrete from one another, but vary continuously
- it is difficult to distinguish one from the other
- characteristics can also be modified by the environment
- differences may therefore be the result of different environmental conditions, rather than different alleles, e.g height of an individual
- for these reasons, inferring DNA differences from observable characteristics has been replaced by directly observing DNA sequences themselves.
47
comparison of DNA base sequences
- in computerised systems, each nucleotide base can be tagged with different coloured fluorescent dye
- this produces a series of coloured bands, each of which represent one of the four bases
- when one species gives rise to another species during evolution, the DNA of the new species will initially be very similar to the species that gave rise to it
- due to mutations, the sequence of bases in the DNA of the new species will change over time
- species that are more closely related show more similarity in base sequences
- as there are millions of base sequences in every organism, DNA contains a vast amount of information about the genetic diversity and evolutionary history of all organisms
48
comparison of mRNA base sequence
- mRNA is coded for by DNA
- the base sequences on mRNA are complementary to those of the strand of DNA from which they were made
49
comparison of amino acid sequences in proteins
- primary protein structure = determined by mRNA = determined by DNA
50
why random sampling may still not be representative
- sample bias
- by chance
51
method of random sampling
1. divide the study area into a grid of numbered lines
2. using a random number generator, obtain a series of coordinates
3. take samples at the intersections of each pair of coordinates
52
how to minimise the effect of change in random sampling
use a large sample size
- the more individuals that are selected, the smaller the probability that chance will influence the results, and the less influence anomalies will have, so the more reliable the data will be
analysis of the data collect
- accepting that chance will play a part, the data collected can be analysed using statistical tests to determine the extend to which chance may have influenced the data
- these tests allow us to decide whether any variation observed is the result of chance or is more likely to have some other cause
53
mean vs standard deviation in distribution curves
mean = max height of the curve
- useful when comparing one sample with another
- does not provide information about the range of values within the sample
standard deviation = measure of the width of the curve
- indicates the range of values about the mean
54
to ensure results = accurate and reliable
- repeat experiment
- large sample size + representative
- calculate mean
- reduces uncertainty
55
random sampling advantages/ disadvantages
advantages
- more manageable numbers
- reflects whole population
- cheaper
- quicker to investigate
disadvantages
- can introduce bias
- increases chances of error
- makes assumptions
56
range vs SD
range- quote largest/smallest
- only uses 2 data points out of set so less reliable than SD
- and can be affected by outliers
SD
- measure of spread of values about the mean
- reduces effect of anomolies
- allows statistical use whether or not differences = significant
