Module 4: Genetic Information, Variation & Relationships Flashcards
Describe prokaryotic DNA?
- Short, circular DNA molecules
- Not associated with histones
- Free floating in the cytoplasm
- Majority is coding DNA
Describe eukaryotic DNA?
- Long, linear DNA molecules
- Associated with histones
- Majority is non-coding DNA
- Located in the nucleus
What is a gene?
A gene is the base sequence of DNA that codes for a polypeptide or functional RNA.
What is a locus?
The fixed position of a gene on a particular DNA molecule.
What is a triplet?
A sequence of three DNA bases.
What are three features of the genetic code?
- Degenerate (some amino acids are coded for by more than one base triplet).
- Universal (each triplet codes for the same amino acids in all organisms).
- Non-overlapping (each base triplet is read once in the sequence & separate from the triplet before it and after it).
What is a codon?
Sequence of three bases on DNA.
What is an anticodon?
A group of three bases on a tRNA molecule.
What is an intron?
A non-coding sequence of bases within a gene.
What is an exon?
A sequence of bases within a gene that code for an amino acid.
What are multiple repeats?
Regions of non-coding DNA base sequences that are repeating.
What is the genome?
The complete set of genes in a cell.
What is the proteome?
The full range of proteins a cell is able to produce.
What is transcription?
The process where the DNA code is copied into mRNA.
What is translation?
The process where mRNA joins with a ribosome for protein synthesis to occur
Describe the structure of mRNA
- Linear shape
- Single polynucleotide strand
- A group of three adjacent bases form a codon
Describe the structure of tRNA
- Clover shape
- Single polynucleotide strand
- Hydrogen bonds present between specific base pairs
- Has an amino acid binding site at one end
- Specific sequence of three bases form an anticodon at the other end
Where does transcription occur in eukaryotes?
The nucleus
Where does transcription occur in prokaryotes?
The cytoplasm
What is the process of transcription?
- RNA polymerase attaches to DNA double helix.
- DNA helicase on RNA polymerase breaks hydrogen bonds between the two DNA strands, unwinding the DNA to expose the bases.
- One DNA strand acts as a template.
- The free RNA nucleotides are attracted to the exposed bases on the template strand & bind via complementary base pairing.
- RNA polymerase reforms the hydrogen bonds & the strands coil back into a double helix, forming pre-mRNA.
- RNA polymerase detaches from the DNA strand when it reaches a ‘stop’ triplet.
What is produced during transcription in a prokaryote?
mRNA
What is produced during transcription in a eukaryote?
pre-mRNA (containing introns & exons).
What is splicing?
The process of removing introns & joining exons in a pre-mRNA strand to form mRNA.
What is the process of translation?
- mRNA binds to the ribosome at the start codon.
- A tRNA molecule carries a specific amino acid (with a complimentary anti codon) binds to the codon on the mRNA molecule.
- A second tRNA molecule binds to the next codon on the mRNA.
- The two amino acids attached to the tRNA molecules are joined by a peptide bond (hydrolysis of ATP provides the energy).
- The first tRNA molecule moves away leaving behind its amino acid.
- The ribosome moves along the mRNA to produce the polypeptide chain
Where does translation occur in prokaryotes & eukaryotes?
At the ribosomes in the cytoplasm.
What are alleles?
Alleles are different versions of the same gene with a slightly different base sequence. They code for different versions of the same polypeptide.
What is a gene mutation?
A gene mutation is a change in the DNA base sequence of chromosomes that can occur spontaneously during DNA replication.
What is a substitution mutation?
A mutation where one base is substituted with another base (e.g. ATGCCT becomes ATTCCT as G is swapped for T).
What is a deletion mutation?
A mutation where one base is deleted (e.g. ATGCCT becomes ATCCT as G is removed).
Why don’t all substitution mutations result in changes to the amino acid sequence.
Due to the degenerate nature of the genetic code, some amino acids are coded for by more than one DNA triplet. Therefore, some substitutions will still code for the same amino acid.
Why does a deletion substitution always result in changes to the amino acid sequence.
Because the deletion of a base changes the number of bases present which causes a frame shift in all the base triplets read after it.
What is a mutagenic agent?
- A mutagenic agent causes an increase in the rate of gene mutations & increases the probability of a mutation occurring.
What are chromosome mutations caused by & how do they occur?
- Chromosome mutations are caused by errors in meiosis (cell division).
- They occur when the cell produced has variations in the number of chromosomes (e.g. they don’t possess 23 whole chromosomes).
What can chromosome mutations lead to?
They can lead to inherited conditions.
What are some examples of mutagenic agents?
- Ultraviolet radiation
- Ionisation radiation
- Some chemicals
- Some viruses
Why do chromosome mutations lead to inherited conditions?
Because the errors are present in the gametes (the hereditary cells).
What is a non-disjunction chromosome mutation?
- Non-disjunction is the failure of the chromosomes to separate properly.
- Non-disjunction of chromosome 21 can lead to Down’s syndrome.
Why is random fertilisation important?
- Because it produces zygotes with different combinations of chromosomes.
- It increases genetic diversity within a species.
Where does meiosis occur?
It occurs in the reproductive organs of multicellular, eukaryotic organisms.
Explain the process of meiosis?
- The DNA unravels & replicates to produce two copies of each chromosome (chromatids).
- DNA condenses to form double-armed chromosomes (each made from two sister chromatids joined by a centromere).
- Meiosis I - the chromosomes arrange themselves into homologous pairs & then separate, halving the chromosome number.
- Meiosis II - the pair of sister chromatids that make up each chromosome are separated.
- Produces four haploid cells that are genetically different.
Name the two main events during meiosis that lead to genetic variation.
- Crossing over of chromatids.
- Independent segregation of chromosomes.
Explain the process of crossing over.
- Occurs during meiosis I when the homologous chromosomes pair up.
- The chromatids twist around each other & bits of chromatids swap over.
- The chromatids still contain the same genes but now possess a different combination of alleles.
Explain how independent segregation of chromosomes leads to genetic variation.
- When the homologous pairs of chromosomes separate during meiosis I, it’s completely random which chromosome ends up with which daughter cell.
Compare the differences between mitosis & meiosis
Mitosis:
- Produces cells with the same number of chromosomes as the parent cell.
- Daughter cells are genetically identical to each other & to the parent cell.
- Produces 2 daughter cells.
- 1 division occurs.
Meiosis:
- Produces cells with haploid number of chromosomes as parent cell.
- Daughter cells are genetically different to one another & parent cell.
- Produces 4 daughter cells.
- 2 divisions occur.
What is genetic diversity?
Genetic diversity is the number of different alleles of genes in a species or population.
How is genetic diversity within a population increased?
- Mutations in the DNA forming new alleles.
- Different alleles being introduced into a population when individuals from another population migrate into it & reproduce (gene flow).
- Crossing over/independent segregation.
- Random fertilisation of gametes.
What is a genetic bottleneck?
A genetic bottleneck is an event that causes a large reduction in a population (e.g. when a large number of organisms within a population die before reproducing).
How does a genetic bottleneck reduce genetic diversity?
When a large number of organisms die before successfully reproducing, it reduces the number of alleles in the gene pool.
What is the founder effect?
The founder effect describes what happens when a few organisms from a population start a new colony so there are only a small number of different alleles in the initial gene pool.
How can the founder effect occur?
It can occur as a result of migration leading to geographical separation (or if the new colony is separated from the original population for another reason e.g. religion).
What is natural selection?
When organisms with a beneficial allele survive & those who don’t possess the beneficial allele die out.
Explain the process of natural selection
- There is differential reproductive success as individuals with a beneficial allele that increases their chances of survival are more likely to survive, reproduce & pass on the beneficial allele compared to those that don’t possess the beneficial allele.
- A greater proportion of the next generation inherits the beneficial allele.
- In turn, they are more likely to survive, reproduce & pass on the beneficial allele.
- The frequency of the beneficial allele increases from generation to generation.
- Over generations this leads to evolution as the advantageous alleles become more common in the population.
What are the three types of adaptations?
- Behavioural
- Physiological
- Anatomical
What is a behavioural adaptation?
Ways in which an organism acts to increase its chance of survival (e.g. playing dead to escape attack).
What is a physiological adaptation?
Processes inside an organism’s body that increases its chance of survival (e.g. during hibernation, metabolism decreases to conserve energy).
What is an anatomical adaptation?
Structural features of an organism’s body that increase its chance of survival (e.g. a thick layer of fat for insulation).
What are the two types of natural selection?
- Directional selection
- Stabilising selection
What is directional selection?
Directional selection is where individuals with alleles for characteristics of an extreme type are more likely to survive & reproduce.
What are the properties of directional selection?
- Can occur in response to an environmental change.
- The mean in the population represents optimum for existing conditions.
- Environmental change may produce a new selection pressure that favours an extreme characteristic.
- Therefore, optimum characteristics necessary for survival change.
- Some organisms will possess the optimum already due to mutation so creates an allele that gives them advantage in new environment.
- over time, selection means these will become the majority & mean will shift.
OR
- Selection pressure at one end of distribution favours the extreme.
- This skews the distribution in one direction forming a new mode.
- This increases evolutionary change.
- The mode changes but frequency remains the same.
What is an example of directional selection?
- Antibiotic resistance
- Presence of antibiotic on non-resistance bacteria.
- This favours resistant bacteria.
- Resistant bacteria become the most common.
- Bacteria evolve to all become antibiotic resistant bacteria.
How do antibiotic resistant bacteria develop resistance to multiple antibiotics?
- Due to random mutation an allele for resistance may already exist in the population.
- When an antibiotic is used, this creates a selection pressure in the environment.
- The allele for resistance gives bacteria a selective advantage.
- The bacteria is more likely to survive & reproduce than those without the allele.
- Some of the offspring inherit the allele for resistance.
- Over time the frequency of the resistant allele increases eventually developing a population resistance to the bacteria.
- This is an example of directional selection.
- A new antibiotic is used which creates a selection pressure.
- This process is repeated & creates a population resistant to both the new and old antibiotic.
- This continues to repeat until the bacteria are resistant to multiple antibiotics.
What is stabilising selection?
Stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to survive & reproduce.
What are the properties of stabilising selection?
- Occurs in populations with a stable environment.
- Selection pressures at both ends of distribution.
- The intermediate becomes the mode & eliminates the extremes.
- Reduces the range of possible characteristics in the population.
- Reduces opportunity for evolutionary change.
- Reduces variability-size of range in population.
- The mode stays the same but frequency of the mode increases.
What is an example of stabilising selection?
- Human birth weight
- Large & small weight babies are more likely to die.
- Conditions favour medium weight babies so are more likely to survive.
- There is a small range of birth weights.
- Humans remain around the same birth weight as time progresses.
What is classification?
Classification is the arrangement of animals/plants in taxonomic groups according to their observed similarities.
What is phylogeny?
Phylogeny is the study of evolutionary history of groups of organisms.
What does phylogeny show?
It identifies how closely related organisms are.
How can phylogeny be presented?
A phylogenetic tree.
What is taxonomy?
Taxonomy is the science of classification - it involves naming organisms & organising them into groups which makes them easier to identify and study.
What are the eight levels of groups called?
Taxon (plural is taxa).
What is meant by a ‘hierarchy’ of groups?
- Smaller groups are placed within larger groups.
- Organisms can only belong to one group so there is no overlap.
Name the eight taxonomic groups used in classification.
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
What are the three domains?
- Eukarya
- Bacteria
- Archaea
What happens as you move down the hierarchy?
- There are more groups at each level but fewer organisms in each group.
- The organisms in each group are more closely related.
What is a species?
A species is a group of similar organisms that are able to successfully reproduce to produce fertile offspring.
What is the nomenclature system used for classification?
The binomial system.
For humans the binomial name is homo sapien. What is the genus & what is the species?
The genus is Homo & the species is sapien.
What is courtship behaviour?
Courtship behaviour is the behaviour carried out by organisms in an attempt to attract a mate.
Name three examples of simple courtship behaviours.
- Releasing a chemical (e.g. pheromones)
- Using sound
- Visual displays
Name two examples of complex courtship behaviours?
- Dancing
- Building (e.g. shelters)
Why is courtship behaviour species specific?
So only members of the same species will perform & respond to the courtship behaviour.
What does the specificity of courtship behaviour prevent/allow?
It allows members of the same species to recognise each other & prevent interbreeding, making reproduction more successful.
Why can courtship behaviour be used to classify organisms?
The behaviour is specific to each species so more closely related species will have similar courtship behaviour.
Name three technologies used for clarifying evolutionary relationships?
- Genome sequencing
- Comparing amino acid sequences
- Immunological comparisons
How can genome sequencing be used to clarify how closely related two species are?
- The DNA base sequence of one organism can be compared to the DNA base sequence of another organism.
- The more similar the DNA base sequences of the two organisms, the more closely related.
How can amino acid sequences be used to clarify how closely related two species are?
- Related organisms will have a similar DNA base sequence so will also have a similar amino acid sequence in their proteins.
How can immunology comparisons be used to clarify how closely related two species are?
- Similar proteins will bind to the same antibodies.
How can genetic diversity be measured?
Measured by comparing:
- The frequency of measurable or observable characteristics.
- The base sequence of DNA.
- The base sequence of mRNA.
- The amino acid sequence of the proteins encoded by DNA/mRNA.
What is standard deviation?
The measure of the spread of values about the mean.
What is biodiversity?
Biodiversity is the variety of living organisms in an area.
What is a habitat?
A habitat is the place where an organism lives (e.g. a field).
What is a community?
A community is all the populations of different species in a habitat.
Name the two ways biodiversity can be measured?
- Species richness
- Index of diversity
What is species richness?
Species richness is the measure of the number of different species in a community.
How is species richness measured.
It can be calculated by taking random samples of a community & counting the number of different species.
What are the limitations of species richness?
The population samples have to be random & may be time consuming or unrepresentative.
Why is index of diversity better than species richness?
Index of diversity takes into account both the number of species in a community & the population size of each species as opposed to just the number of species in a community.
What does a high value for index of diversity indicate?
A high number indicates a diverse area.
What is the index of diversity if all of the individuals are the same species?
1
Why is woodland clearance done?
Woodland clearance is done to increase the area of farmland.
What is the effect of woodland clearance on biodiversity?
- It destroys habitats so some species may lose their shelter/food source.
- This may cause species to die or be force to migrate, reducing biodiversity.
What are pesticides & why are they used?
- Pesticides are chemicals that kill organisms that feed on crops (pests).
- They are used to increase the number of crops produced for sale.
What is hedgerow removal & how does it affect biodiversity?
- Hedgerow removal increases the area of farmland by turning many small fields into fewer large fields.
- This reduces the number of hedges so the species die or migrate, reducing biodiversity.
Describe two ways the use of pesticides reduces biodiversity.
- Killing the pests reduced diversity.
- Also kills any species that rely on the pests as a food source or forces these species to migrate.
What are herbicides & what are their effects on biodiversity.
- Herbicides are chemicals that kill unwanted plants (weeds).
- They reduce plant diversity & reduce the number of organisms that use the weeds as a food source.
What is monoculture & what is its effect on biodiversity?
- Monoculture is when farmers have fields containing only one type of plant.
- It reduces biodiversity & supports fewer organisms as a habitat or food source.
What are conservation schemes?
Conservation schemes are schemes that aim to protect the environment, bringing a balance between agriculture & biodiversity.
Give three examples of conservation schemes?
- Legal protection for endangered species.
- Creating protected areas.
- Schemes that encourage farmers to increase biodiversity.
What is a Spearman’s rank correlation coefficient used for?
It is used to measure the correlation between two variables.
Explain the results of a Spearman’s rank test.
+1 = Strong positive correlation
0 = No correlation
-1 = Strong negative correlation
