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A Level Biology > 4 Genes > Flashcards

4 Genes Flashcards

1
Q

What is a gene?

A

A section of DNA that contains the coded information for making polypeptides and functional RNA. The coded information is in the form of a specific sequence of bases along the DNA molecule. Polypeptides make up proteins and so genes determine the proteins of an organism. Enzymes are proteins. As enzymes control chemical reactions they are responsible for an organisms development and activities. In other words genes, along with environmental factors, determine the nature and development of organisms. A gene is a section of DNA located at a particular position called a Locus on a section on a DNA molecule.

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2
Q

The gene is a base sequence of DNA that codes for:

A

The amino acid sequence of a polypeptide

A functional RNA, including ribosomal RNA and transfer RNAs

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3
Q

The genetic code

A

In trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of three bases that coded for each amino acid.
As the code has three bases for each amino acid, each one is called a triplet. As there are 64 possible triplets and only 20 amino acids, it follows that some amino acids are coded for by more than one triplet

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4
Q

What were the scientists reasoning behind thinking there are a minimum of three bases?

A

– Only 20 different amino acids regularly occur in proteins.
– Each amino acid must have its own code of bases of the DNA
– if each base coded for a different amino acid, only four different amino acid’s could be coded for
– only four different bases are present in DNA
- using a pair of bases, 16 different codes are possible, which is still in adequate
– three bases produce 64 different codes, more than enough to satisfy the requirements of 20 amino acids

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5
Q

Features of the genetic code

A

– A few amino acids are coded for by only a single triplet
– the remaining amino acids are coded for by between two and six triplets each
– the code is known as a degenerate code because most amino acids are coded for by more than one triplet
-A triplet is always read in one particular direction along the DNA strand
- The start of the DNA sequence that codes for a polypeptide is always the same triplet. This code is for the amino acid methionine. If the first Methionine molecule does not form part of the final polypeptide, it is later removed
– three triplets do not code for any amino acid. These are called stop codes and mark the end of the polypeptide chain. They act in much the same way as a full stop at the end of a sentence
– The code is non-overlapping, in other words each base in the sequence is read only once. Thus six bases numbered 123456 are read as triplets 123 and 456, rather than as triplets 123, 234, 345, 456.
– The code is universal, with a few minor exceptions each triplet code is for the same amino acid in all organisms. This is indirect evidence for evolution

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6
Q

Why does lots of the DNA in eukaryotes not code for polypeptides?

A

Between the genes that are non-coding sequences made up of multiple repeats of base sequences. Even within genes, only certain sequences code for amino acids. These coding sequences are called exons. Within the gene these exons are separated by further non-coding sequences called introns. Some genes code for ribosomal RNA and transfer RNAs

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7
Q

Exons

A

Sequences that code for amino acids in genes

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8
Q

Introns

A

Non-coding sequences within genes that separates the exons

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9
Q

What is DNA like in prokaryotic cells?

A

The DNA molecules are shorter than eukaryotic DNA, form a circle and are not associated with protein molecules. Prokaryotic cells therefore do not have chromosomes

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10
Q

What is DNA like in eukaryotic cells?

A

The DNA molecules are longer than prokaryotic DNA, form a line rather than a circle and occur in association with proteins called histones to form structures called chromosomes. The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotic cells, is short, circular and not associated with proteins

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11
Q

Chromosome structure

A

They are only visible as distinct structures when a cell is dividing. For the rest of the time they are widely dispersed throughout the nucleus. When they become visible at the start of cell division chromosomes appear as two threads, joint at single point. Each thread is called a chromatid because DNA has already replicated to give two identical DNA molecules. The DNA in chromosomes is held by histones. The considerable length of DNA found in each cell is highly coiled and folded

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12
Q

Homologous chromosomes

A

Sexually produced organisms, such as humans, are the result of the fusion of a sperm and an egg, each of which contributes one complete set of chromosomes to the offspring. Therefore, one of each pair is derived from the chromosomes provided by the mother in the egg and the other is derived from the chromosome provided by the father in the sperm. These are known as homologous pairs and the total number is referred to as the diploid number. In humans this is 46
Homologous pair is always two chromosomes that carry the same genes but not necessarily the same alleles of the genes.

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13
Q

Allele

A

Is one of a number of alternative forms of a gene. Genes are sections of DNA that contain coded information in the form of specific sequences of bases. Each gene exists as two, occasionally more different forms. Each of these forms is called an allele. Each individual inherits one allele from each of its parents. These two alleles may be the same or they may be different. When they are different, each allele has a different base sequence, therefore a different amino acid sequence, so produces a different polypeptide

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14
Q

Transferring coded information

A

The messenger RNA transfers the DNA code from the nucleus to the cytoplasm. It is small enough to leave the nucleus through the nuclear pores and to enter the cytoplasm, where the coded info that it contains is used to determine the sequence of amino acids in the proteins which are synthesised there

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15
Q

Codon

A

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

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16
Q

Genome

A

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

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17
Q

Proteome

A

The full range of proteins produced by the genome. This is sometimes called the compete proteome, in which case the term proteome refers to the proteins produced by a given type of cell under a certain set of conditions

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18
Q

Ribonucleic Acid structure

A

RNA is a Polymer made up of repeating mononucleotide sub units
It forms a single strand in which 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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19
Q

Which two types of RNA are important in protein synthesis?

A

Messenger RNA

transfer RNA

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20
Q

Messenger RNA

A

A long strand that is arranged in a single helix
The base sequence of mRNA is determined by the sequence of bases on a length of DNA in a process called transcription
Once formed, mRNA leaves the nucleus via pores in the nuclear envelope and enters the cytoplasm, where it associates with the ribosomes
There is acts as a template for protein synthesis
Its structure is suited to this function because is possesses information in the form of codons
The sequence of codons determines the AA sequence of a specific polypeptide that will be made

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21
Q

Transfer RNA

A

A relatively small molecule that is made up of around 80 nucleotides
It is a single stranded chain folded into a clover leaf shape, with one end of the chain extending beyond the other
This is the part of the tRNA molecule to which an AA can easily attach
There are many types of tRNA, each of which binds to a specific AA
At the opposite end of the tRNA molecule is a sequence of three other organic bases, known as the anticodon
Given that the genetic code is degenerate there must be as many tRNA molecules as there are coding triplets
However each tRNA is specific to one AA and has an anticodon that is specific to that AA

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22
Q

Complementary base pairings that RNA forms:

A

Guanine with cytosine

Adenine with uracil (in RNA) or thymine (in DNA)

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23
Q

Transcription

A

The process of making pre-mRNA using part of the DNA as a template
An enzyme acts on a specific region of dna causing the two strands to separate and expose the nucleotide bases in that region
The nucleotide bases on one of the two dna strands, known as the template strand, pair with their complementary nucleotide from the pool which is present in the nucleus. The enzyme RNA polymerase then moves along the strand and joins the nucleotides together to form a pre mRNA molecule
As the rna polymerase adds the nucleotides one at a time to build a strand of pre-mRNA, the dna strands rejoin behind it. As a result, only about 12 base pairs on the dna are exposed at any one time
When the rna polymerase reaches a particular sequence of bases on the dna that it recognises as a stop triplet code, it detaches, and the production of pre-mRNA is then complete

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24
Q

Splicing of pre-mRNA

A

In prokaryotic cells, transcription results directly in the production of mRNA from DNA. In eukaryotic cells transcription results in the production of pre-mRNA, which is then spliced to form mRNA. The dna of a gene eukaryotic cells is made up of sections called exons that code for proteins and sections called introns that don’t. These intervening introns would prevent the synthesis of a polypeptide. In the pre-mRNA of eukaryotic cells. The base sequences corresponding to the introns are removed and the functional exons are joined together during a process called splicing
As most prokaryotic cells don’t have introns, splicing of their dna is unnecessary
The mRNA molecules are too big to diffuse out of the nucleus and so, once they have been spliced, they leave via a nuclear pore. Outside the nucleus, the mRNA is attracted to the ribosomes to which it becomes attached, ready for the next stage of the process: translation

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25
Q

Synthesising a polypeptide

A

Once mRNA has passed out to the nuclear pore it determines the synthesis of a polypeptide.
A ribosome becomes attached to the starting codon at one end of the mRNA molecule
The tRNA molecule with the complementary anticodon sequence moves to the ribosome and pairs up with the codon on the mRNA. This tRNA carries a specific amino acid
A tRNA molecule with a complementary anticodon pairs with the next codon on the mRNA. This tRNA molecule carries another amino acid
The ribosome moves along the mRNA, bringing together two tRNA molecules at any one time, each pairing up with the corresponding two codons on the mRNA
The two AAs on the tRNA are joined by a peptide bond using an enzyme and ATP which is hydrolysed to provide the energy required
The ribosome moves on to the third codon in the sequence on the mRNA, thereby linking the AAs on the second and third tRNA molecules
As this happens, the first tRNA is released from its AA and is free to collect another AA from the AA pool in the cell
The process continues in this way, with up to 15 amino acids being added each second, until a polypeptide chain is built up
Up to 50 ribosomes can pass immediately behind the first, so many identical polypeptides can be assembled simultaneously
The synthesis of the polypeptide continues until a ribosome reaches a stop codon. At this point, the ribosome, mRNA and the last tRNA molecule all separate and the polypeptide chain is complete

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26
Q

Assembling a protein

A

The polypeptide is coiled or folded, producing its secondary structure
The secondary structure is folded, producing the tertiary structure
Different polypeptide chains, along with any non protein groups, are linked to form the quaternary structure

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27
Q

Mutation

A

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

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28
Q

Gene mutation

A

Any change to one or more nucleotide bases, or a change in the sequence of the bases, in DNA

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29
Q

Types of gene mutations

A

Substitution of bases

Deletion of bases

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30
Q

Substitution of bases

A

A nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
The significance of this difference all depends upon the precise role of the original amino acid. If it is important in forming bonds that determine the tertiary structure of the final protein, then the replacement amino acid may not form the same bonds. The protein may then be a different shape and therefore not function properly.
The effect of the mutation is different if the new triplet of bases still code for the same amino acid as before. This is due to the degenerate nature of the genetic code, in which most amino acids have more than one codon.

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31
Q

Deletion of bases

A

The nucleotide is lost from the normal DNA sequence. Loss of a single nucleotide from the thousands in a typical gene may seem a minor change but the consequences can be considerable. Usually the amino acid sequence of the polypeptide is entirely different and so the polypeptide is unlikely to function correctly. This is because the sequence of bases in DNA is read in units of three bases (triplet).
One deleted nucleotide causes all triplets in a sequence to be read differently because each has been shifted to the left by one

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32
Q

Chromosome mutations

A

Changes in the structure or number of whole chromosomes are called chromosome mutations
Chromosome mutations can arise spontaneously and take two forms:
– changes in whole sets of chromosomes
– changes in the number of individual chromosomes

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33
Q

Changes in whole sets of chromosomes

A

Occurs when organisms have three or more sets of chromosomes rather than the usual two. This condition is called polyploidy and occurs mostly in plants

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34
Q

Changes in the number of individual chromosomes

A

Sometimes individual homologous pairs of chromosomes fail to separate during meiosis. This is known as nondisjunction and usually results in a gametes having either one more or one fewer chromosome. On fertilisation with a gamete that has the normal complement of chromosomes, the resultant offspring have more or fewer chromosomes than normal in all the body cells. An example of a nondisjunction in humans is Down’s syndrome, where individuals have an additional chromosome 21

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35
Q

Cell division occurs in two ways:

A

Mitosis – produces two daughter cells with the same number of chromosomes as the parent cells and as each other
Meiosis – usually produces four daughter cells, each with half the number of chromosomes as the parent cell

36
Q

Importance of meiosis

A

In sexual reproduction two gametes fuse to give rise to new offspring. If each gamete had a full set of chromosomes (diploid number) and the cell that they produce has double this number. In humans, the different number of chromosomes is 46, which means that this cell would have 92 chromosomes.
This doubling of the number of chromosomes would continue at each generation. It follows that, in order to maintain a constant number of chromosomes in adults of species, the number of chromosomes must be halved at some stage in the life-cycle. This halving occurs as a result of meiosis. In most animals meiosis occurs in the formation of gametes.
Every diploid cell of an organism has two complete sets of chromosomes: one set provided by each parent. During meiosis , homologous pairs of chromosomes separate, so that only one chromosome from each pair enters a daughter cell. This is known as the haploid number of chromosomes which, in humans, is 23. When two haploid gametes fuse at fertilisation, the diploid number of chromosomes is restored

37
Q

The process of meiosis

A

Meiosis involves two nuclear divisions that normally occur immediately one after another:

  1. In the first division (meiosis 1) homologous chromosomes pair up and the chromatids wraparound each other. Equivalent portions of these chromatids may be exchanged in a process called 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
  2. In the second meiotic division (meiosis 2) the chromatids move apart. At the end of meiosis two, four cells have usually been formed. In humans each of these cells contain 23 chromosomes
38
Q

Meiosis brings about genetic variation in what two ways?

A

Independent segregation of homologous chromosomes

New combinations of maternal and paternal alleles by crossing over

39
Q

Gene

A

A length of DNA that codes for a polypeptide

40
Q

Locus

A

The position of a gene on chromosome or DNA molecule

41
Q

Allele

A

One of the different forms of a particular gene

42
Q

Homologous chromosomes

A

A pair of chromosomes, one maternal and one paternal, that have the same gene Loci

43
Q

Independent segregation of homologous chromosomes

A

During meiosis one, each chromosome lines up alongside it’s homologous partner. In humans, for example, this means that there will be 23 homologous pairs of chromosomes lying side-by-side. When these homologous pairs arrange themselves in this line they do so at random. One of each pair will pass to each daughter cell. Which one of the pair goes into the daughter cell, and with which one of any of the 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. This is called independent segregation

44
Q

Variety from new genetic combinations

A

Each member of a homologous pair of chromosomes has exactly the same genes and therefore determines the same characteristics (e.g. tongue rolling and blood-group). However, the alleles of these genes may differ (e.g. they may code for rollers or non-rollers). The independent assortment, of these chromosomes therefore produces new genetic combinations.
Where the cells produced in meiosis are gametes these will be genetically different as a result of the different combinations of the maternal and paternal chromosomes/alleles they contain. These haploid gametes fuse randomly at fertilisation. The haploid gametes produced by meiosis fuse to restore the diploid state. Each gamete has a different make up and the random fusion therefore produces variety in the offspring. Where the gametes come from different parents two different genetic make ups are combined and even more variety results

45
Q

Genetic recombination by crossing over

A

The chromatids of each pair become twisted around one another
During this twisting process tensions are created and portions of the chromatids breakoff
These broken portions might then rejoin the chromatids of its homologous partner
Usually it is the equivalent portions of homologous chromosomes that are exchanged
In this way new genetic combinations of maternal and paternal alleles are produced

If there is no recombination by crossing over only two different types of cell are produced. However, if recombination does occur, four different cell types are produced.

46
Q

Possible chromosome combinations following meiosis

A

It is possible to make a mathematical calculation based on the number of chromosomes in an organism to determine the number of possible combinations of chromosomes for each daughter cell. The formula is:
2^n where n= the number of pairs of homologous chromosomes

Where the gametes come from different parents two different genetic complements with different alleles are combined, providing yet more variety. Again, we can calculate this mathematically using this formula:
(2^n)^2

47
Q

Genetic diversity

A

DNA determines the considerable variety of proteins that make up each organism. Therefore genetic similarities and differences between organisms may be defined in terms of variation in DNA. Hence it is differences in DNA that lead to the vast genetic diversity we find on Earth.
A section of DNA that codes for one polypeptide is called a gene. All members of the same species have the same genes. For example, all humans have a gene for blood-group. Which blood-group humans have depends on which two alleles of the gene they possess.
Genetic diversity is described as the total number of different alleles in a population. The greater the number of different alleles that all members of the same species possess, the greater the genetic diversity of that species. The greater the genetic diversity, the more likely that some individuals in a population will survive an environmental change

48
Q

Population

A

A group of individuals of the same species that live in the same place and can interbreed

49
Q

Why does a greater genetic diversity make it more likely that some individuals in a population will survive an environmental change?

A

Because of a wider range of alleles and therefore a wider range of characteristics. This gives a greater probability that some individual will possess a characteristic that suits it to the new environmental conditions. Genetic diversity is a factor that enables natural selection to occur

50
Q

Natural selection in the evolution of populations

A

Not all alleles of a population are equally likely to be passed to the next generation. This is because only certain individuals are reproductively successful and so pass on their alleles

51
Q

Reproductive success and allele frequency

A

Differences between the reproductive success of individuals affects allele frequency in populations. The process works like this:
With any new population of species there will be a gene pool containing a wide righty of alleles.
Random mutation of alleles within this gene pool may result in a new allele of a gene which in most cases will be harmful
However in certain environments, the new allele of the gene might give its possessor an advantage over other individuals in the population.
These individuals will be better adapted and therefore more likely to survive in their competition with others
These individuals are more likely to obtain the available resources and so grow more rapidly and live longer. As a result, 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 in turn are more likely to survive, and so reproduce successfully.
Over many generations, the number of individuals with the new ‘advantageous’ allele will increase at the expense of the individuals with the ‘less advantageous’ alleles.
Over time, the frequency of the new, advantageous alleles in the population increases while that of the non-advantageous ones decreases

52
Q

Selection

A

The process by which organisms that are better adapted to their environment tend to survive and breed, all those that are less well adapted tend not to. Every organism is subjected to a process of selection, based on its suitability for surviving the conditions that exist at the time. Different environmental conditions favour different characteristics in the population. Depending on which characteristics are favoured, selection will produce a number of different results
Most characteristics are influenced by more than one gene (polygenes). These types of characteristics are more influenced by the environment than ones determined by a single gene

53
Q

What are the two types of selection?

A

Directional and stabilising

54
Q

Directional selection

A

If the environmental conditions change, the phenotypes that are best suited to the new conditions are most likely to survive. Some individuals, which fall to either the left or right of the mean, will possess a phenotype more suited to the new conditions. These individuals will be more likely to survive and breed. They will therefore contribute more offspring to the next generation than other individuals. Over time, the mean will then move in the direction of these individuals.
Directional selection therefore results in phenotypes at one extreme of the population being selected for and those at the other extreme being selected against

55
Q

Stabilising selection

A

If environmental conditions remain stable, it is the individuals with phenotypes closest to the mean that are favoured. These individuals are more likely to pass their alleles on to the next generation. Those individuals with phenotypes at the extremes are less likely to pass on the alleles. Stabilising selection therefore tends to eliminate the phenotypes at the extremes.

56
Q

Natural selection results in species that are better adapted to the environment that they live in. These adaptions may be:

A

Anatomical – such a shorter ears and thicker fur in Artic foxes compared to foxes in warmer climates
Physiological – oxidising of fats rather than carbohydrate in kangaroo rats to produce additional water in the a dry desert environment
Behavioural – such as the autumn migration of swallows from the UK to Africa to avoid food shortages in the UK winters

57
Q

Species

A

Members of a species are capable of breeding to produce living, fertile offspring. They are therefore able to produce more offspring. This means that, when a species reproduces sexually, any of the genes of its individuals can, in theory, be combined with any other

58
Q

Binomial System

A

Organism’s are identified by two names

  • it is a universal system based upon Latin or Greek names
  • the first name, called the generic name, denotes the genus to which the organism belongs, this is equivalent to the surname used to identify people and shared by their close relatives
  • the second name, called the specific name, denotes the species to which the organism belongs. This is equivalent to the first name used to identify people

The names are printed in italics or underlined if handwritten
If the specific name isn’t known is can be written as sp. e.g. Felix sp.

59
Q

Classification

A

The grouping of an organism

60
Q

Courtship behaviour enables individuals to:

A
  • recognise members of their own species to ensure that mating only takes place between members of the same species
  • identify a mate that is capable of breeding because both partners need to be sexually mature, fertile and receptive to mating
  • form a pair bond that will lead to successful mating and raising of offspring
  • synchronise mating so that it takes place when there is the maximum possibility of the sperm and egg meeting
  • becoming able to breed by bringing a member of the opposite sex into a physiological state that allows breeding to occur
61
Q

Biodiversity

A

Term used to describe variety in the living world
Refers to the number and variety of living organisms in a particular area
Has 3 components:
-species diversity
-genetic diversity
-ecosystem diversity

62
Q

Species diversity

A

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

63
Q

Genetic diversity

A

Refers to the variety of genes possessed by the individuals that make up a population of a species

64
Q

Ecosystem diversity

A

Refers to the range of different habitats, from a small local habitat to the whole of the earth

65
Q

Species richness

A

A measure of species diversity
The number of different species in a particular area at a given time (community). Two communities may have the same number of species but the proportions of the community made up of each species may differ markedly.

66
Q

Measuring the index of diversity

A

d= N(N-1)/sum of n(n-1)

d= index of diversity
N=total number of organisms of all species
n=total number of organisms of each species

67
Q

Impact of agriculture

A

Agriculture ecosystems are controlled by humans. 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 needs to be large. Any particular area can only support a certain amount of biomass. If most of the area is taken up by the one species that the farmer considers desirable, it follows that there is a smaller area available for all the other species. These many other species have to compete for what little space and resources that are available. Many won’t survive. Even if species are evolved to adapt to the changes, the population of the species would be considerably reduced. In addition, pesticides are used to exclude these species because they compete for the light, mineral ions, water and food required by the farmed species. The overall effect is a reduction in species diversity. The index of species diversity is therefore low in agriculture ecosystems

68
Q

What practices have directly removed habitats and reduced species diversity?

A

Removal of hedge rows and grubbing out woodland
Creating monocultures, for example replacing natural Meadows with cereal crops or grass for silage
Filling in ponds and draining Marsh and other wetland
Overgrazing of land, for example upland areas by sheep, thereby preventing regeneration of woodland

69
Q

What practices have indirectly removed habitats and reduced species diversity?

A

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 or undersowing

70
Q

What management techniques can be applied to increase species and habitat diversity, without unduly raising food costs or lowering yields?

A

Maintain existing hedgerows at the most beneficial height and shape. A-shape better than rectangular
Plant hedges rather than erect fences as Field boundaries
Maintain existing ponds and where possible 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 the use of pesticides – use biological control where possible or genetically modified organisms that are resistant to pests
Use organic, rather than 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 the verges and field edges until after flowering and when seeds of dispersed
Introduce conservation headlands – areas at the edges of fields where pesticides are used restrictively so that wildflowers and insects can breed

71
Q

Comparison of observable characteristics to look at genetic diversity

A

Traditionally genetic diversity was measured by observing the characteristics of organisms. This method is 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 (plus environmental influences).
Using observable characteristics has its limitations because a large number of them are coded for by more than one gene. They’re polygenic. This means that they are not discrete from one another but rather vary continuously. It is often difficult to distinguish one from another. Characteristics can also be modified by the environment. Differences may therefore be the results of different environmental conditions rather than different alleles. Height in humans for example is determined by a number of genes. However, environmental factors like diet can influence the actual height of an individual.
For these reasons, inferring DNA differences from observable characteristics has been replaced by directly observing DNA sequences themselves. This has been made possible through the advances in gene technology made over recent years.

72
Q

Comparison of DNA base sequences to look at genetic diversity

A

Using various techniques, we can now actually determine the exact order of nucleotides on DNA. We can measure the genetic diversity of the species by sampling the DNA of its members and sequencing it to produce a pattern of coloured bands. Analysis of these patterns allow us to compare one species with another or one individual with another of the same species to determine how diverse they are.
When one species gives rise to another species 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 of the new species will change. Consequently, over time, the new species will accumulate more and more differences in its DNA. As a result, we would expect species that are more closely related to show more similarity in their DNA base sequences than species that are more distantly related. 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.

73
Q

Comparison of the base sequence of mRNA to look at genetic diversity

A

The base sequences on mRNA are complimentary to those with the strands of DNA from which they were made. It follows that we can measure DNA diversity, and therefore genetic diversity, by comparing the base sequence of mRNA

74
Q

Comparison of amino acid sequences in proteins to look at genetic diversity

A

The sequence of amino acids in proteins is determined by mRNA which, in turn, is determined by DNA. Genetic diversity within, and between species can therefore be measured by comparing the amino acid sequences of their proteins. The degree of similarity in the AA sequence of the same protein in two species will also reflect how closely related the two species are. Once the AA sequence for a chosen protein has been determined for two species, the two sequences are compared. This can be done by counting either the number of similarities or the number of differences in each sequence.

75
Q

Interspecific variation

A

Differences between organisms of different species

76
Q

Intraspecific variation

A

Differences between organisms of the same species

77
Q

Why might sampling not be representative?

A
  • sampling bias

- chance

78
Q

Sampling bias

A

The selection process may be biased. The investigators may be making unrepresentative choices, either deliberately or unwittingly

79
Q

Chance

A

Even if sampling bias is avoided, the individuals chosen may, by pure chance, not be representative

80
Q

How can you prevent sampling bias?

A

Carry out random sampling
Divide the study area into a grid of numbered lines
Using random numbers, from a table or generated by a computer, obtain a series of coordinates
Take samples at the intersection of each pair of coordinates

81
Q

How can you minimise chance in sampling?

A

Use a larger sample size

Analysis of the data collected

82
Q

Normal distribution curve

A

Bell shaped
Symmetrical about a central value
Mean mode and median at highest point- when symmetrical

83
Q

Skewed distribution

A

When moved to right- mode is highest. Mean to the left. Median further to left
Vice versa for moved to left

84
Q

Standard deviation of a normal distribution curve

A

A measure of the width of the curve. It gives an indication of the range of values either side of the mean. A standard deviation is the distance from the mean to the point where the curve changes from being convex to concave. 68% of all the measurements lie within +-1.0 standard deviation. Increasing this width to almost +-2.0 standard deviations takes 95% of all measurements

85
Q

Calculating standard deviation

A

Square root (sum of (measured value - mean value)^2/total number of values in sample -1)

A Level Biology (20 decks)

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