Genetic diversity + adaptation - Chapter 9 +biodiversity- Chapter 10 Flashcards
What is gene mutation ?
Any change to one or more nucleotide bases or a change in the sequence of bases in the DNA
When can gene mutation arise, and what do they include ?
They can arise spontaneously during DNA replication and include base substitution, base deletion or base addition
What is location ?
Germline in gametes or somatic in body cells
What are the two types of gene mutations ?
1) Point mutation
2) Frameshift mutations
What is a point mutation ?
A change in a single nucleotide (also known as substitution)
What is a frameshift mutation ?
Addition or deletion of nucleotides resulting in a shift of the reading frame
What are the three types of point mutations ?
1) Silent point mutation
2) Nonsense point mutation
3) Missense point mutation
What is a silent mutation ?
There is no change to the primary structure of the polypeptide despite the change in a nucleotide base
[If a substitution does not change the amino acid)
Why is a silent mutation possible?
Due to the degenerate nature of the genetic code.
Mutation would have no effect on the production of the final polypeptide
What is a missense mutation ?
There is a change to a single amino acid at the point of the mutation
[If a substitution changes the amino acid ]
What is the effect of a missense mutation ?
It will be determined by the role of the amino acid in the final polypeptide.
( May be that it was involved in the formation of bonds to structure the active site of an enzyme )
What does a missense mutation occur due to ?
A mutation in the hameoglobin gene
What is a nonsense mutation ?
The new codon is now a stop codon so translation stops at the point of mutation
[If a substitution changes the amino acid to a “stop” ]
What does a nonsense mutation lead to ?
The premature end to the synthesis of a polypeptide
What is a reading frame?
A way of dividing the sequence of nucleotides on a DNA/RNA molecule into consecutive,
non- overlapping triplets
What is deletion mutation (type of frameshift mutation) ?
A base is lost /deleted
This occurs when a nucleotide is lost from the DNA sequence
What can deleting a base lead to ?
The codons not being read properly.
This is due to the fact bases are read in triplets, therefore the subsequent bases would all be shifted forward by one base ( a frameshift )
Usually the amino acid sequence of the ‘new’ code will be entirely different
What will happen to the reading frame + bases when deleting a base ?
The reading frame changes, the bases don’t move
What is base insertion (type of frameshift mutation) ?
The insertion (addition) of a single nucleotide base
[ an extra base is added/ inserted ]
What will happen to the amino acid sequence in base insertion + deletion mutation ?
The amino acid sequence codes for something different
Define the term mutagenic agent ?
A factor that increases the rate of mutations
What is the importance of meiosis?
In sexual reproduction, two gametes fuse to give rise to new offspring.
It is responsible for the formation of gametes
What are the gametes in humans ?
Egg + sperm
What are the gametes in plants ?
Egg + pollen
What is the difference between meiosis compared to mitosis?
Meiosis: two nuclear divisions, haploid cells (one set of chromosomes), introduces genetic variation
Mitosis: one nuclear division, diploid cells ( two sets of chromosomes ), create genetically identical cells
What is the process in crossing over of chromatids ?
- Homologous pairs of chromosomes associate/form a bivalent
- Chiasmata form
- Equal lengths of (non-sister) chromatids / alleles are exchanged
- Producing new combinations of alleles
[When homologous chromosome pairs line up opposite each other at the equator in meiosis 1, the non -sister chromatids of the two chromosomes wrap around each other : called crossing -over
- This puts tension on the chromatids, causing pairs of the chromatids to break off, and exchange between the homologous chromosomes
- because the chromosomes have exchanged DNA, that means they exchange alleles, so crossing over results in new combinations of alleles ]
What is a bivalent ?
The attached pair of chromosomes
What is chiasmata ?
The points where the chromatids are joined
What causes genetic variation in meiosis?
[Chiasmata can form at multiple points so a large number of alleles can be exchanged]
This exchange of alleles is a major source of genetic variation in meiosis
Unlike mitosis, where does cell division by meiosis only take place in ?
Sex organs, producing gametes
What does meiosis produce
4 haploid cells from a single diploid cell
What type of chromosomes do gametes have ?
Individual chromosomes, not pairs
Why is it important that gametes are haploid cells?
During fertilisation, gametes fuse together to produce a fertilised egg (zygote)
What are homologous chromosomes ?
Chromosomes of similar length with the same genes at the same loci
What is independent segregation (detailed explanation ) ?
In meiosis 1, homologous pairs of chromosomes line up opposite each other at the equator of the cell.
It is random which side of the equator the paternal + maternal chromosomes from each homologous pair lie.
These pairs separated, so one of each homologous pair ends up in the daughter cell
What does independent segregation create?
A large number of possible combinations of chromosomes in the daughter cells produced
How are the large number of possible combinations of chromosomes in the daughter cells produced calculated ?
2^n
2= chromosome pairs (2 chromosomes each time )
n = number of homologous pairs
What happens in meiosis 1 and 2?
In meiosis 1, homologous chromosomes are separated from each other
In meiosis 2, sister chromatids are separated from each other, producing 4 haploid cells
What are the stages of meiosis ?
Interphase 1, prophase 1, metaphase 1, anaphase 1, telophase 1, cytokinesis, prophase 2, metaphase 2, anaphase 2, telophase 2, cytokinesis
What is interphase 1 ?
[same stage as mitosis stage ]
Before meiosis starts, the cell will have been through interphase
During interphase, DNA replicates (S phase), the cell copies the chromosomes and the organelles (chromosomes not visible)
First the cell enters meiosis 1
What happens in prophase 1?
- the chromosomes condense and become visible
- homologous chromosomes link together forming chiasmata
- At this point, crossing over can take place, exchanging alleles between homologous chromosomes
- the nuclear membrane also breaks down
- the centrioles move to opposite poles of the cell
- spindle fibres also start to assemble into the spindle apparatus
What happens in metaphase 1?
The pairs of homologous chromosomes are now lined up on the equator of the spindle apparatus
What happens in anaphase 1?
- The spindle fibres shorten and the homologous chromosomes move towards opposite poles
~~> for this to happen, the chiasmata between homologous chromosomes break
What happens in telophase 1?
- The chromosomes have now reached the poles of the cell
- At this point, the nuclear membranes reform and the chromosomes uncoil back to their chromatin state
What happens in cytokinesis?
- cell undergoes cytokinesis, dividing into two cells
~~> these cells are haploid, because they no longer contain pairs of homologous chromosomes
What happens in prophase 2?
- the chromosomes condense + become visible again
- Again the nuclear membrane breaks down and spindle fibres begin to develop
What happens in metaphase 2?
- the chromosomes are lined up on the equator of the spindle apparatus
What happens in anaphase 2?
- the centromere of each chromosome divides
- the spindle fibres shorten
- the sister chromatids are now pulled towards opposite poles of the cell
What happens in telophase 2 ?
- the sister chromatids have reached the poles of the cells : chromosomes
- the nuclear membranes reform + the chromosomes uncoil back to their chromatin state
What happens in cytokinesis, after meiosis 2 ?
Each cell undergoes cytokinesis to produce 2 haploid cells
How can mutations in the number of chromosomes arise spontaneously by ?
Chromosome non-disjunction during meiosis
What does non - disjunction mean?
When the chromosomes or chromatids do not split equally during anaphase
(Detailed explanation :
Sometimes the homologous pairs of chromosomes/chromatids - depending on stage of meiosis
fail to separate leading to the production of gametes with one too many or one too few chromosomes
What are 2 possibilities of chromosome mutation ?
- Aneuploidy
- Polyploidy
What is aneuploidy ?
Changes in the number of individual chromosomes leads to aneuploidy (n+1 or n-1) , happens usually in anaphase
What is polyploidy ?
Changes in the number of whole sets of chromosomes can lead to polyploidy (2n gametes)
What happens to the chromosomes when it is polyploidy for non-disjunction in meiosis 1 ?
Look at notes for diagram
Each homologous pair is doubled due to DNA replication in interphase
Non-disjunction in meiosis 1 : all chromosomes fail to separate equally
Normal division in meiosis 2 : chromosomes separate equally
Results:
2n gamete (diploid), 2n gamete (diploid), and 2x no chromosomes in gamete
How does triploid (3n) happen ?
When 2n gamete (mutated gamete- diploid) fuses with n gamete (normal haploid gamete - 1 copy of homologous pair) creating a triploid (3n)
Changes in whole sets of chromosomes occur when organisms have 3 or more sets of chromosomes rather than the usual 2
(If it happened again, ends up with 4 sets)
What happens to the chromosome when it is polyploidy for non-disjunction in meiosis 2?
Look at notes for diagram
3 homologous chromosomes
Each homologous pair is doubled due to DNA replication in interphase
Normal division in meiosis 1 : chromosomes separate equally
Non-disjunction in meiosis 2 : all chromatids fail to separate equally
Results : n gamete (haploid), n gamete (haploid), no chromosomes, 2n gamete (diploid)
Where does polyploidy occur mostly in ?
Occurs mostly in plants (e.g. ferry) but can happen in animals e.g. salamonelles + frogs are polyploids (if in humans, the zygote created wouldn’t survive)
Occurs when organisms have three or more sets of chromosomes
What does non-disjunction in aneuploidy result in ?
A gamete having one more or one fewer chromosome.
One fertilisation with a gamete that has the normal number of chromosomes, the resultant zygote will have more or fewer chromosomes than normal in all their body cells
What is an example of trisomy ?
Down Syndrome ~> gametes which have an extra chromosome (3 copies of 21 - trisomy), as a result of non-disjunction will cause Down Syndrome
What happens to the chromosomes in aneuploidy for non-disjunction in meiosis 1?
-Each homologous pair is doubled due to DNA replication in interphase
- non-disjunction in meiosis 1: one chromosome does not separate equally
- normal division in meiosis 2 : chromatids separate equally
Results :
n+1 (haploid gamete with 1 additional chromosome), n+1 (haploid gamete with 1 additional chromosome), n-1 ( haploid gamete missing one chromosome), n-1 (haploid gamete missing one chromosome )
What happens to the chromosomes in aneuploidy for non-disjunction in meiosis 2?
-3 homologous chromosomes
- each homologous pair is doubled due to DNA replication in interphase
- Normal division in meiosis 1
- non-disjunction in meiosis 2 - one chromatid fails to separate equally
Results:
n-1 (haploid gamete missing one chromosome), n+1 (haploid gamete with one additional chromosome), n (haploid gamete), n (haploid gamete)
What are mutagenic agents?
A factor that increases the rate of mutations;
What are some examples of mutagenic agents?
- UV light
- ionising particles (alpha, beta, gamma)
- carcinogens
Genetic diversity and adaptation
What is a species?
A group of organisms that are capable of breeding to produce living, fertile offspring
~> variation occurs due to difference in the alleles present
What is genetic diversity?
The total number of different alleles in a population
What is population ?
A group of individuals of the same species that live in the same place + can interbreed
What is a gene pool ?
The number of different alleles across all the genes in a population
When can natural selection only occur ?
If there is genetic diversity within a population
What happens when genetic diversity is reduced ?
The species has fewer different alleles.
This means that the phenotypes of the organisms are all very similar
What does genetic variation allow for ? (What would happen if a sudden change was to take effect in genetic diversity?)
The survival of an offspring
If a sudden change was to take effect, there is a greater chance that the whole population would be wiped out
What does natural selection lead to ?
Evolution in populations
What is evolution ?
The change in allele frequency over many generations in a population
What does natural selection result in ?
Species becoming better adapted to their environment.
Adaptations may be anatomical, physiological or behavioural
(Behavioural, structural, functional )
What is the process of natural selection ?
- New alleles for a gene are created by random mutations, creating variation
- [A random mutation of alleles within this gene pool can make a new phenotype]
If the new alleles increases the chances of the individual to survive in that environment (if the new allele is advantageous) , they are more likely to
survive + reproduce - This reproduction passes on to the advantageous allele to the next generation (the advantageous allele is inherited by members of the next generation )
- As a result, over many generations, the new allele increases in frequency in the population.
What does structural adaptation to species (as a result of natural selection) mean ?
Changes to the physical features of an organism
E.g. shorter ears
What does a functional adaptation of a species (as a result of natural selection ) mean?
Changes to the biological processes to the organism
E.g. oxidising fat rather than carbohydrate in kangaroo rats to produce additional water in a dry desert environment
What does a behavioural adaptation of a species (as a result of natural selection ) mean?
Changes to the behaviour of a species
E.g. In Autumn, migration of swallows from the UK to Africa avoid food shortages in the UK winter
What is directional selection ?
Selection that favours individuals that vary in one direction from the mean of the population
Particular traits that have the selective advantage
What are some key points of directional selection ?
- one of the extremes has the selective advantage
- occurs when there is a change in the environment
- the model trait changes
What is stabilising selection ?
Preserves the average characteristics of population and favours average individuals
What are some key points if stabilising selection ?
- the model trait has a selective advantage
- occurs when there is no change in the environment
- the modal trait remains the same
- standard deviation decreases, as individuals with the extreme trait decrease
What is an example of directional selection ?
- population of birds which use their breaks to open seeds for food
- Beak size varies around the mean, with some birds having a relatively small beak + some having a relatively large beak
- climate is drier ~> plants produce hard seeds
- birds with a smaller beak size struggle to open the seeds for food
- birds with a larger beak size have a selective advantage + are more likely to survive and reproduce
- overtime, the alleles for larger beak size become more common in the gene pool : shifts mean to larger beak size
Summary : as a result of a drought, only large seeds survive to finches with a large beak depth are more likely to survive and reproduce. The average beak depth will eventually shift to be deeper
What is a second example of directional selection - antibiotic resistance in bacteria
- in the absence of antibiotic, resistant bacteria have no advantage over non-resistant bacteria. So number of bacteria with antibiotic resistance is low, in a sense of antibiotic
- However, in the presence of antibiotic, resistant bacteria have a selective advantage. Resistant bacteria can survive + reproduce in the presence of antibiotic, whereas non-resistant bacteria are killed by the antibiotic
- so overtime, the gene for antibiotic resistance becomes more common in the population
So, in directional selection, one phenotype is selected over another phenotype. This takes place when the environment changes.
Environmental change = presence of antibiotic
What is a third example of directional selection ?
-white-winged moths were more numerous than dark-winged moths.
After industrialisation, dark -winged moths became more numerous than white.
Because, during industrialisation, tree trunks covered by white lichen became dark due to deposition of soot
- white -winged moths can easily be picked up by predators from the dark background + dark -winged moths mostly survived
Other stabilising selection key points?
-any extremes of phenotype are selected against
- the individuals with phenotypes closest to the mean are favoured
Alleles closer to the mean become more frequent over time.
-extreme phenotypes are less likely to reproduce
~> so stabilising selection tends to eliminate the phenotypes at the extremes
What is an example of stabilising selection ?
- scientists found that babies with a very low or high birth weight were less likely to survive than those with a birth weight around the mean
- As the graph shows, those at the extremes have higher infant mortality rates
- in this case, the extremes of phenotype are very low birth weight and very high birth weight
Babies born with these birth weights have a higher mortality rate than those born with a birth weight around the mean (genetics play a major role in birth rate) - babies with a very low/very high birth weight are less likely to survive, the alleles contributing to these birth weights are less likely to be passed on,
This means that over time, birth weights will stabilise towards the mean with less variation at the extremes
Directional selection in bacteria
After antibiotics, what strains did we start to see?
Strains of bacteria arising that were not killed by antibiotics. At the time penicillin was the stable antibiotic
How did a mutation lead to antibiotic resistance ?
The bacterium that had developed resistance happened, by pure chance, to be in a situation where penicillin was being used to treat a person’s illness
Use of antibiotics puts directional selection pressure on the bacterial population
Why is antibiotics an example of natural selection ?
- Bacterium survived was able to divide
- introduction of antibiotics cause frequency of alleles to increase, mutations cause antibiotic resistance
- mutations occur randomly + very rare, occasionally they are advantageous, depends on the circumstance
- the advantageous mutation means the mutants will outcompete + replace the original population
What is the transfer of resistant genes?
The genes can be passed down through generations of dividing bacteria (binary fission) once the random mutation has arisen. Through selection, only those with beneficial mutations may survive.
What happens if a gene for resistance is found on a plasmid ?
The gene is passed horizontally to another bacterium through conjugation. A conjugation tube is formed between two bacteria, through which a copy of the donor’s plasmid is passed to the recipient
Biodiversity
What is a species ?
A group of organisms that are capable of breeding to produce living, fertile offspring
What is the binomial system ?
First name is GENUS, second name is SPECIES
Same genus shows close relationship
What do you write if a species is unknown ?
S.p
Why do different species look similar ?
- Live in a similar environment
- Have similar selection pressures
- Similar alleles will have the selective advantage
- Produces similar/same proteins and therefore have similar characteristics
What is a hierarchy ?
Smaller groups arranged within larger groups
No overlaps between groups
What is the classification system?
Domain - Eukarya
Kingdom - Animalia
Phylum - Chordata
Class - Mammalia
Order - Carnivora
Family - eanidae
Genus - vulpes
Species - vulpes vulpes
What is the acronym for the classification system
King Philip Came Over For Good Soup
Why do we need to organise species?
-understand relationships between organisms and keep track of changes
- the system used needs to be universal
- system is based on putting organisms into groups
What was the original way to classify ?
Originally, based on visible similarities - e.g appearance, behaviour
What are more modern and accurate classification methods ?
Comparing genetic diversity :
- DNA sequence (base sequence of DNA)
- mRNA sequence (base sequence of RNA)
- Amino acids sequence
- Immunological - comparing similarity in self - antibody shape
What is phylogenetic classification + what does it tell us ?
Arranges species into groups according to their evolutionary origins and relationships
Phylogeny tells us who’s related to whom and how closely related they are
What have all organisms evolved from ?
Shared common ancestors (relatives).
This is shown on a phylogenetic tree
What are phylogenetic classifications based on ?
Homologous characteristics
What are homologous characteristics ?
These are characteristics in multiple species that all have similar evolutionary origins, regardless of what their function is in adult life.
What is artificial classification ?
Organisms are divided into groups based on physical differences such as colour, size, number of legs, or leaf shape
- these are called analogous characteristics
What are analogous characteristics + an example ?
Characteristics that have the same function but they do not have the same evolutionary origins.
E.g. the wings of butterflies and birds are both used for flight, but they originated in different ways
What is courtship behaviour ?
Behaviours aimed to facilitate attraction and mating with the opposite sex and are very common across the animal kingdom
How do animals keep their species alive?
Animals must mate with other members of their own species if they are able to produce viable, fertile offspring
To be successful in breeding, what must species develop ?
Courtship behaviours that enable them to recognise members of the same species and choose the perfect partner that will offer them healthy offspring to pass on their genes through the generations
What are the 5 advantages of courtship behaviours ?
- Helps members of the same species to recognise each other
- Helps them to identify a mate that is capable of breeding
- It can form pair bonds
- Helps to synchronise mating
- It can enable the act of capsulation (sexual intercourse)
Explain the 5 advantages of courtship behaviours ?
- Helps members of the same species to recognise each other, so that a mating season is not wasted on a e.g bird that just looks similar
- Helps them to identify a mate that is capable of breeding, indicates they are sexually mature + in season [otherwise would not be produced fertile gamete + offspring]
- It can form pair bonds,
For many species, mates will form a bond that allows them to support their offspring together, working with one another to raise the young. Often essential to the survival of the offspring in the wild. - Helps synchronise mating,
So that it only takes place where there is maximum probability of the sperm + egg meeting - It can enable the act of capsulation (sexual intercourse) :
by bringing member of the opposite sex into a physiological state that allows this to occur
What is biodiversity ?
The number + variety of living organisms in a particular area
What are the 3 components of biodiversity ?
- species diversity
- genetic diversity
- ecosystem diversity
What is species diversity ?
The number of different species + individuals of each species within any one community
What is species richness ?
Number of different species in a particular area at a particular time
What is genetic diversity ?
The variety of genes amongst all the individual in a population of a species
What is ecosystem diversity ?
The range of different habitats
How does farming reduce biodiversity ? (And how to prevent this ?)
Woodland + hedgerow clearance : directly removes habitats + reduces species diversity
Prevent by : species adapt to dead woodland
Creating monocultures : directly removed habitats, not enough food so animals die quickly, reduces species diversity
Prevent by : intercropping ~> plant 1 crop and 2nd species of crop besides it
Draining wetlands : destroys habitats, reducing biodiversity
Prevent by : don’t drain all the wetlands, drain a specific pan + leave other area to dry.
Use of pesticides : affect insects particularly important to ecosystem.
Bioaccumulating - infects exposed to pesticides and is eaten, than other animals eats thos animals
Prevent by : use more organic pesticide, use a mesh instead, rotate crops as it builds up less pesticides in soil
What are monocultures?
An area of farm land on which only one crop is grown
How can sampling bias be prevented?
Random sampling
How is random sampling carried out?
- divide the study area into a grid of numbered lines, for example, by stretching two long tape measures at right angles to each other.
- use 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
How can the effect of chance when sampling be reduced?
Large sample size
What are the three domains?
Archaea, bacteria and eukarya
What are the features of the bacteria domain ?
No histones, no membrane bound organelles,70s ribosomes, cell walls are made of murein
What are the features of the archaea domain ?
Genes and membranes contain fatty acids joined to glycerol by ester linkages. If they have a cell wall, it doesn’t contain murein
What are the features of the eukarya domain ?
Contain membrane bound organelles
Membranes contain fatty acids joined to glycerol by ester linkages.
If they have a cell wall, it doesn’t contain murein.
80s ribosomes.
Contains histones.
What does standard deviation tell you ?
Indicates the ranges of values either side of the mean
What are the three different types of averages?
Mean, median , range
What are different types of variation?
Continuous and discountinous
What are the different kinds of graph, chart ?
Bar, scatter, line
