Topic 4 - Genetic Infomation, variaton and relationships between organisms Flashcards
Define Gene
a short section of DNA that codes for a polypeptide or functional RNA
Define allele
a version of a gene
Define locus
a position on a chromosome
Define homologous
the structural features and pattern of genes are the same
For maternal and paternal chromosomes where are same genes found
in the same positions on the chromosomes
The genetic code is:
- Non overlapping
- A triplet code
- Universal
What is meant by a triplet code?
every 3 base pairs (nucleotides) codes for 1 amino acid
What is meant by universal?
the code is the same in all species, ATA codes for the same thing in every species
What is meant by non overlapping?
Each base is discrete (123456 is 123, 456 and NOT 123, 234, 345, 456) so that the bases don’t get mixed up when they are being read, meaning the wrong amino acid is formed
How many possible triplet codes are there?
64
How many possible amino acids are there?
20
The genetic code is degenerate, what does this mean?
Some amino acids are coded by more than one triplet, e.g. tyrosine is TAT or TAC
What do some triplet codes act as?
Some triplet codes act as punctuation marks
Some indicate start and stop points for start/end of an amino acid chain:
- A start codon is ATG
What is transcription?
formation of pre mRNA in the nucleus
What is translation?
formation of polypeptides in the ribosomes
How does transcription work?
.Parental DNA has its hydrogen bonds broken by DNA helicase, leaving a template strand
.Free RNA nucleotides are attracted to it and form weak hydrogen bonds with the DNA nucleotides that are complementary to their bases
.RNA polymerase comes along and resynthesizes the sugar phosphate backbone along the RNA nucleotides and breaks the hydrogen bonds, making a strand of pre mRNA
.The pre mRNA is then spliced, which removes introns and joins together exons, turning into mRNA (no longer pre)
What are introns?
non-coding DNA
What are exons?
coding DNA
What is translation?
The process by which mRNA is used to make a specific protein
Describe how translation happens
Translation is the process by which mRNA is used to make a specific protein, after mRNA has been produced through transcription and splicing it then moves through the cytoplasm to a ribosome and enters between the two sub units and attaches to it. Here a start codon (AUG) tells the ribosome to start reading the RNA on it. Each triplet of bases is called a codon, and after the initial start codon tells the ribosome to read it the ribosome then moves along the mRNA and reads the codons, attaches (with temporary hydrogen bonds) tRNA with a complementary anticodon to the mRNA’s codon. Each tRNA has a specific amino acid attached, as one tRNA binds to the mRNA so does another one next to it, then their amino acids form polypeptide bonds to join them together and the first tRNA leaves and another one joins as the ribosome moves along the mRNA and forms a polypeptide bond in a condensation reaction with the amino acid there. This continues till a stop codon is reached which has no complementary anticodon so the chain stops and the polypeptide chain formed leaves the ribosome and coils up into an amino acid which join using energy from ATP.
What does tRNA do?
.Transport specific amino acids
How many different tRNA’s are there?
20
Do all tRNA’s have the same structure?
Yes
What is a tRNA made up of?
codon, anti codon, hydrogen bonds, ester bonds, amino acids
Describe the structure of tRNA
.Each consists of a single polynucleotide strand of RNA
.Folded to form a clover arrangement
.Held in place by hydrogen bonds between complementary base pairs
.One end acts as an attachment site for the amino acid
.The other end is called the anti-codon
What is a mutation?
Any change in one or more nucleotide base or a change in the sequence of the bases in DNA
Characteristic of mutations
.Random
.Spontaneous
.Natural
.Positive or negative
Three types of mutations
.Insertion
.Deletion
.Substitution
Define insertion
A nucleotide is added to the DNA sequence
Define deletion
A nucleotide is lost from the DNA sequence
Define subsitution
One nucleotide is replaced by another nucleotide with a different base
What is a frame shift?
every amino acid after the insertion or deletion will move one place
What will substitution affect?
Only one triplet code
What will deletion and insertion affect?
the whole amino acid sequence, by causing a frame shift
What is a mutagen?
A physical or chemical agent that changes the genetic material of an organism
What do mutagenic agents do?
increase the frequency of a mutation occurring above the natural
Name 4 things that act as mutagenic agents
Caffeine, x-rays, mustard gas and UV radiation
What are chromosomal mutations?
Changes in the structure or number of whole chromosomes
What are the two types of chromosomal mutations?
.Polyploidy
.Nondisjunction
What is polyploidy?
.Changes in whole sets of chromosomes
.Cells have multiple sets of chromosomes
What form of polyploidy is very common in plants?
.3n = triploid
What is non-disjunction?
.Homologous pairs fail to separate
.Changes in number of individual chromosomes per cell
What is down’s syndrome caused by?
extra chromosome 21
Define meiosis
the process by which a diploid nucleus (2n) divides to produce four haploid daughter nuclei (n)
Name the phases in meiosis
Interphase, prophase I, Metaphase I, Anaphase I, Telophase I, cytokinesis, Prophase II, Metaphase II, Anaphase II, telophase II and cytokinesis
What is a homogolous pair?
one chromatid of mum and one chromatid of dad
What are sister chromatids?
identical chromatids together
What two forms of genetic variation are there?
Crossing over and independent segregation
What is crossing over?
Crossing over is the exchange of alleles
What is independent segregation?
Independent segregation is the random arrangement of chromosomes
State what happens in each phase of meiosis.
Interphase – The cell is synthesising DNA and checking it (2 chromatid per chromosome)
Prophase I – The chromosomes thicken and get bigger, shorten and condense, the nuclear membrane breaks down
Metaphase I – The chromosomes line up along the equator and attach the spindle fibres from the poles to their centromeres
Anaphase I – The pair of chromosomes are split as each is pulled to opposite poles in the cell by the spindle fibres contracting – the homologous chromosomes are separated from each other but the chromosome stays tgther
Telophase I & Cytokinesis – The cells form two nucleus, one for each set of new chromosomes, and pull apart while forming a membrane to produce two daughter cells
Prophase II – The chromosomes thicken and get bigger, shorten and condense, the nuclear membrane breaks down
Metaphase II – The chromosomes line up along the equator and attach the spindle fibres from the poles to their centromeres
Anaphase II – The sister chromatids are split as each chromatid is pulled to opposite poles in the cell by the spindle fibres
Telophase II & cytokinesis – The cells form two nucleus, one for each set of new chromatids, and pull apart while forming a membrane to produce two more daughter cells each (4 cells now altogether)
What is a genotype?
The genetic makeup of an organism, the genes and alleles that they have
What is a phenotype?
Observable characteristics, genotype + environment = phenotype
What are the causes of genetic variation?
.Mutations, sexual reproduction, meiosis
How does crossing over work?
Homologous pairs line up, chromatids of each pair become twisted, section of chromatid breaks off and re-joins chromatid of the other homologous chromosome, sections have different alleles, new combination of linked alleles
With crossing over, what happends to the amount of possible versions of allele combinations?
No crossing over = 2 versions
With crossing over = 4 possible versions
Who discovered independent segregation? When?
.Gregor Mendel (19th Century)
What is independent segregation?
the random segregation of chromosomes during anaphase
What did Gregor Mendel say about independent segregation?
.Genes are inherited independently of one another
.BUT genes close together have a high likelihood of being inherited together
Independent segregation key points
.Homologous pairs line up along the equator randomly
.Combination of chromosomes pulled to each pole is random
.Daughter cells produced are genetically different
The formula for the number of combinations of genes after independent segregation
2^n
The formula for the number of combinations of genes after fertilisation after independent segregation
(2^n)^2
Why does the formula (2^n)^2 not work for crossing over?
Crossing over is completely random
What is the ‘n’ in the formula (2^n)^2?
number of chromosomes
What is the first ‘2’ in the formula (2^n)^2?
possible number of routes the chromosomes could go to (pulled to two poles)
Define genetic diversity
The total number of different alleles in a population
What must happen for a genetic mutation to occur?
.There must be a change in the DNA
.A random mutation
.Resulting in:
.Polyploidy, non-disjunction, substitution, insertion, deletion
High genetic diversity within a species =
large number of different alleles
Low genetic diversity within a species =
small number of different alleles
Advantages of High Genetic DIversity
.Higher survival rate, we might have some people with genes to survive in certain climates and some who don’t, if we had LGD and all had the other climates genes we would all die
.Higher resistance to disease, as it won’t spread as easily
.Low chance of inbreeding
.Less competition for same habitat
.Larger food web, not solely reliant on one food
Disadvantages of High Genetic DIversity
.Fewer organisms with characteristics for human’s
.Fewer organisms adapted to an environment at a specific time or place
What is natural selection?
The differential survival and reproduction of individuals due to differences in their phenotype
Define phenotype
Observable physical characteristics that an organism has
Define genotype
Genetic makeup of an organism
Define allele frequency
The number of times an allele occurs within in the gene pool
Define genepool
The total number of alleles in a particular population at a specific time
Why does allele frequency change?
Not all alleles are equally likely to be passed to the next generation
Those better adapted to their environment tend to survive and breed, at the expense of those less well adapted
Key points of a normal distribution curve
.No bias
.Data surrounds a central point
.Curve is symmetrical
.Curve is bell shaped
Mode
The most frequent value
Mean
the average, every value added together divided by the amount of values
Median
the value in the middle when the in ascending order
Describe the shape of a normal distribution curve
The curve is shaped like a bell, near 0 on the y axis at the extremes of the x axis and increasing like a curve to a maximum in the middle
In a normal distribution curve, what is the mean the same as?
The mode and the median
Why does the mean of a distribution curve change?
Most characteristics area a result of multiple genes (poly genes)
Each gene is affected by the environment
Changes in environment = changes in the mean
How does directional selection occur?
- Mutation occurs
- Change in the environment occurs
- Selection favours individuals that vary in one direction from the mean
- One extreme is favoured for
- Allele frequency changes
Define selection
The process by which organisms that are better adapted to their environment tend to survive and breed at the expense of those less well adapted.
Essentially, what is directional selection?
.Phenotypes of one extreme in the population is selected for
.The other phenotype is selected against
.Change in allele frequency
In stabilising selection, what happens?
.Selection acts against both extremes in a range of phenotypes .Mean is favoured .Phenotypic variation is reduced .Both extremes are selected against .Environment has remained stable
Why is birth rate an example of stabilising selection?
.The extremes are favoured against since too low or too high birth weights can result in death of the child
.Too low, going to die
.Too high, going to take lots of resources and energy from the mother when alive or could kill the mother in birth so a low survival rate for the baby
What is aseptic technique?
‘Method designed to prevents contamination form microorganisms’
When is aseptic technique important?
.Handling surgical equipment
.Surgery
.During labour
.Inserting catheters or IV drips
Phenotype selected, directional selection
The one best suited to the changing environment, one of the extremes
Phenotype selected, Stabilising selection
The mean/medium/mode
Effect on the characteristics of a population, directional selection
Changes the overall characteristics to make it advantageous in the given environment
Effect on the characteristics of a population, stabilising selection
Increases the frequency of the mean/medium/mode allele at the expense of the extreme alleles to make the population as a whole better suited to their stable environment
Shape of the distribution curve, directional selection
Shifts the normal curve to one extreme or the other
Shape of the stabilising curve, directional selection
Narrows the normal curve and increases its height (frequency) for the mean/medium/mode
Example, directional selection
Moths in the industrial revolution or antibiotic resistance
Example, stabilising selection
Weight of babies after birth
What is a species?
A species is a group of individuals that area capable of breeding to produce living and fertile offspring.
What happens to a species genes in sexual reproduction?
Two individuals of a species can combine their genes during sexual reproduction but selection can act to favour different phenotypes presence within species depending on where they are found
What is an anatomical adaptation? Example
Anatomical – structure, how the organism is shaped – appearance, e.g. shorter ears and thicker fur in arctic foxes
What is an physiological adaptation? Example
inside, how the organism works internally – chemical reactions/processes internally, e.g. oxidising of fat rather than carbohydrates to produce extra water
What is a behavioural adaptation? Example
behaviour, how you the organism acts – actions of the organisms, e.g. migration of swallows from UK to Africa
Key information of binomial names
.Universal naming system
.Written in italics or underlined
.Given two names
What is the first name in binomial names?
Generic name
.Denotes the genus
.Upper case
What is the second name in binomial names?
Used to identify
.Denotes the species
.Lower case
Binomial names, order of Latin things
Kingdom Phylum Class Order Family Genus Species
State the difference between pre-mRNA and mRNA
mRNA has introns removed
Birth weight is a form of stabilizing selection, why?
Both extremes have a disadvantage, too heavy or too light and it’ll die
Why is splicing required?
So it is small enough to leave the nuclear envelope and doesn’t disrupt the formation of a polypeptide
Examples of courtship displays
.Bright colours .Patterns .Feathers .Birds tweeting/songs .Building rock piles .Fighting .Ritualised movements (dancing) .Displays of beauty or strength
Stimuli to male response of a courtship display happening
Stimuli the male communicates a courtship signal this acts as a visual stimulus to the females and is detected by the eyes (a receptor) sends a message to female nervous system (CNS) effector contracts or releases a hormone effector causes a specific innate/stereotyped behaviour of her own (response) acts as a stimulus to the male the male responds
Why do males impress the females?
They are the ones that are needed to carry the children
Why are courtship displays important?
they help an organism to reproduce
How do courtship displays help an organism to reproduce?
- Enabling an organism to recognise one of their own species – so they can produce fertile off spring and prevent cross breeding, ensures genes are passed on, use similarities in physical characteristics and behaviours
- Identifying if a mate is capable of breeding – both partners need to be sexually mature, fertile and receptive to mating, females may only be ‘in season’ once a year
- Forming pair bonds (lifelong pairings) – ensures successful breeding (more investment), successful raising of the offspring/pass on genes
- Synchronising mating season – determines whether the female is in receptive (fertile) state, correct female response then mating will take place
Define classification
the organisation of living organisms into groups
Define taxonomy
the theory and practice of biological classification
Key points of classification
Carl Linnaeus
Not random
Based on accepted principles
Define analogous
have the same function but do not have the same evolutionary origin
Define homologous
similar evolutionary origins/structures regardless of their function
What is artificial classification? With example
Based on analogous classification
Not based on evolutionary relationship
For example, wings on a bat and a butterfly
What is phylogenetic classification?
Classifies species based on shared features
Characteristics derived from ancestors
Based on evolutionary relationships
Partly based on homologous characteristics
What is each group called in phylogenetic classification?
a taxon (taxa)
Who developed domains and what are they?
Carl Woese developed domains – the highest taxonomic rank
Name the 3 domains
Bacteria, archea and eukarya
Key features of bacteria
Unicellular Non-membrane bound organelle Non-membrane bound DNA Has plasmids Has 70S ribosomes Small DNA is free floating DNA is not associated with histones Cell wall (murein) Some may cause disease
Key features of archea
Single celled prokaryotes Similar shape and size to bacteria DNA/genes and protein synthesis like eukaryotes No murein in cell wall No membrane bound organelle
Key features of eukrya
Multicellular Membrane bound organelle Membrane bound DNA Doesn’t have plasmids Has 70S and 80S ribosomes Large DNA is in the nucleus DNA is associated with histones (proteins) No cell wall Split into four kingdoms (protoctista, fungi, plantas, animals)
How to read phylogenetic trees
Oldest ancestral species at base, most recent divergence at the end of branches
Define hierarchy
smaller groups within larger groups with no overlap
Advantages of classifying by observable characteristics
.Easier
.Anybody could do it
.Does not require any advanced equipment
Disadvantages of classifying by observable charcateristcs
.Patterns of inheritance aren’t always clear
.Differences aren’t often discrete
.Interpretation subjective
.Fossil data is hard to find
.Most genes are polygenetic
.May be a result of similar environments not similar evolutionary history
How can DNA Base Sequences be used to see evolutionary relationships?
Compare the exact order of nucleotides on the DNA
Mutation occurs causing a difference between individuals
More differences in bases = fewer similarities
Individuals more distantly related
How can mRNA Base Sequences be used to see evolutionary relationships?
mRNA is complementary to DNA
Differences in mRNA = differences in DNA
Compare the exact order of nucleotides on the DNA
Mutation occurs causing a difference between individuals
More differences in bases = fewer similarities
Individuals more distantly related
How can amino acid sequences in proteins be used to see evolutionary relationships?
Differences in DNA = differences in mRNA
Differences in mRNA = differences in amino acids
Compare the exact order of nucleotides on the DNA
Mutation occurs causing a difference between individuals
More differences in bases = fewer similarities
Individuals more distantly related
Adv of using DNA and mRNA when finding evolutionary relationships
.Determine the exact order of nucleotide bases
.Determine how diverse organisms are
.Determine the time since divergence through the number of mutations present
Disadv of using DNA and mRNA when finding evolutionary relationships
.Can cost a lot
.Can take a long time to sequence the full genome
.Requires specialist equipment and personnel
Adv of using amino acids when finding evolutionary relationships
.Determines the DNA and mRNA sequence
.Usually easier to identify amino acids present
Disadv of using amino acids when finding evolutionary relationships
.Can cost a lot
.Can take a long time
.DNA may be non-coding so not detected as difference
.The genetic code is degenerate so the same amino acid may be a result of very different DNA sequences
How can we identify genetic diversity?
.DNA Hybridisation
.Biochemical analysis
What is hybrid?
combination of two different elements
What is DNA hybridisation?
direct comparison between the DNA sequences of different organisms
What is a hybrid strand?
one strand from one set of DNA and one strand from another
How does DNA Hybridisation work?
- DNA from two species is heated
- Denatures DNA and breaks the hydrogen bonds
- Strand A given radioactive labels or fluorescent markers
- Strand A and B are mixed
- Strands are cooled
- Two strands recombine and hydrogen bonds can reform between
- Gaps are present when no complimentary base pairing has occurred
- The higher percentage f hydrogen bonds formed = greater similarity in genetic material
How does biochemical analysis work?
Serum containing many human antigens is injected into another species, rabbits are commonly used. The rabbit responds by producing anti-human antibodies, anti-human antibodies from rabbit are extracted in a serum and mixed with other species. The antihuman antibodies will bind to human antigens in the serum of other species, the more human like antigens in the serum (similar in structure), the more antigen-antibody complexes formed (as they are complementary), the more precipitate seen in the serum. The more precipitate seen, then the more closely related to the human the other species are (if there is similarity in protein structure, there is similarity in DNA).
In biochemical analysis, the human serum first must be added to a different species, why?
so that antibodies complementary to the human antigens can be formed, and then used to test for the complementary human antigens
Why are species like rabbits used in biochemical analysis?
Species like rabbits are used since they are small, easy to keep, produce lots of young and cheap
Define biodiversity
The range and variety of genes, species and habitats within a particular region.
What are the 3 types of biodiversity?
Species diversity, genetic diversity and ecosystem diversity
What is species diversity?
the number of different species and the number of individuals of each species within any one community
What is genetic diversity?
the variety of genes possessed by the individuals that make up any one species
What is ecosystem diversity?
the range of different habitats within a particular area
What is species richness?
Species richness is the number of different species in a particular area at a given time (community)
Equation for species diversity index? With meaning for each letter
d = species diversity N = total number of organisms of all species n = total number of organisms of each species Σ = the sum of
Human factors affecting biodiversity
.Agriculture – demand for food has more than doubled
.Increased use of herbicides and pesticides
.Use land for homes and industry
.Increased waste and land fill
.Deforestation
How does agriculture affect biodiversity?
- Monoculture (growing only one species)
- Lack of intercropping (not rotating what is grown each season)
- Competition for space
- Use of pesticides and herbicides
- Cattle in the field where species may grow
- Draining wetland and marshes
- Removing hedgerows (replacing hedge borders with fences)
How do monocultures affect biodiversity?
reduction in species and genetic diversity directly and indirectly as fewer food sources and habitats
how does lack of intercropping affect biodiversity?
Drains the soil of nutrients, results in monoculture
How does competition for space affect biodiversity?
Natural species habitats cannot grow/are outcompeted by dominant
How does use of pesticides and herbicides affect biodiversity?
Can be toxic to species, enters water cycle, eutrophication
How does cattle in the field where species may grow affect biodiversity?
Over grazing, trampling, reduction in species diversity
How does draining wetland and marches affect biodiversity?
Removes nutrients and moisture from soil so species cannot grow
How does removing hedgerows affect biodiversity?
Removes habitats and food sources
What is deforestation?
The permanent clearing of forests and the conversion of land to other uses, such as agriculture, grazing or settlement
How many species are being lost each year due to deforestation?
50,000
How does deforestation reduce biodiversity?
by clearing the forests you are not only killing the trees (a species) and so reducing the species diversity index directly but the trees may also act as a habitat or food source to other animals so by killing the trees you are killing the animals that rely on the tree as well – thereby indirectly reducing biodiversity as well.
How can maintaining biodiversity bring economic benefit?
- By maintaining biodiversity, you can keep biodiverse areas (like the coral reef or forests) which attract tourists and people for days out, thereby benefiting the economy. Also extracts of plants can be used for medicine, so you keep the biodiversity and keep the money.
How can you reduce human impacts of deforestation?
.Eco charges
.Increased taxes/fines
Define intraspecific
variation within a species, eye colour or blood group
Define interspecific
variation between a species, food source or pollinator
State when you would use quadrats and transects with examples
- You use quadrats to compare how common an organism is in two or more sample areas (shady and sunny spots in a playing field). You use transects to find out how organisms are distributed across an area (if an organism becomes more or less common as you move from a hedge towards the middle of a field).
How would you use quadrats?
Place a 1m^2 quadrat on the ground at a random point within the first sample area, count all the organisms within that quadrat, repeat as many times as possible, work out the mean number of organisms per quadrat within the first sample area. Repeat this all for the second sample area. Compare the two means.
How would you use trasects?
Mark out a line in the area you want to study using a tape measure, collect data along this line (this can be done by counting the amount of organisms touching the line or by placing quadrats down as you go down the line at even intervals). Interpret the data.
What is sampling bias and how is it avoided?
- Biased choices made by the investigator
- Deliberate or unwillingly
- Sample is unrepresentative
- Avoided using random sampling
What is chance variation and how is it avoided?
- Even if sampling bias is avoided, this can still occur
- Not a representative sample
- I.E. all individuals are the same
- Avoided by increasing sample size
- Repeat lots
Define distribution
the way in which data is spread/shared out
What is standard deviation a form of?
A statistical test
What is standard deviation and what does it do?
.A measure of the width of the curve
.Indicates of the range
.The distance from the mean until the curve goes from convex to concave
.Determines how likely it is that results are due to chance
With standard deviation, the closer to the mean values (less spread), the ____ reliable
more
__% of data lies within 1 s.d
68
__% of data lies within 2 s.d
95
Standard deviation equation
root((Σ(x-(Σx/n))^2)/(n-1))
