T4: Genetic Information & Variation Flashcards
What are the components of nucleotides?
- pentose sugar
- phosphate group
- an organic nitrogenous base
Describe how a phosphodiester bond is formed between two nucleotides within a DNA
molecule. (2)
- Condensation (reaction)/loss of water;
- (Between) phosphate and deoxyribose;
- (Catalysed by) DNA polymerase;
In the process of semi-conservative DNA replication, the two strands within a DNA molecule are separated. Each then acts as a template for the formation of a new complementary strand.
Describe how the separation of strands occurs. (2)
- DNA helicase;
- Breaks hydrogen bonds between base pairs/ AT and GC/complementary bases
OR
Breaks hydrogen bonds between polynucleotide strands;
Reject hydrolysis of hydrogen bonds
The nucleus and a chloroplast of a plant cell both contain DNA. Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus. (3)
In chloroplasts:
1. DNA shorter;
Accept smaller
2. Fewer genes;
3. DNA circular not linear;
4. Not associated with protein/histones, unlike nuclear DNA;
5. Introns absent but present in nuclear DNA;
Must be comparative statements.
DNA is a polymer of nucleotides. Each nucleotide contains an organic base.
Explain how the organic bases help to stabilise the structure of DNA. (2)
- Hydrogen bonds between the base pairs holds two strands together
- Many hydrogen bonds provides strength
Describe FOUR differences between the structure of a tRNA molecule and the structure of an
mRNA molecule. (4)
- tRNA is ‘clover leaf shape’, mRNA is linear;
- tRNA has hydrogen bonds, mRNA does not;
- tRNA has an amino acid binding site, mRNA does not;
Accept ‘CCA end’ for amino acid binding site - tRNA has anticodon, mRNA has codon;
Must be a comparison
what is a codon?
- triplets of bases that code for a particular amino acid
What is the genetic code?
- the order of bases on DNA
- ## consitsts of codons ( triplets of bases that code for a particular amino acid)
Why is the genetic code described as being universal? (1)
- (In all organisms / DNA,) the same triplet codes for the same amino acid;
Define a gene
- a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule
give the functions of the three types of RNA.
mRNA - the bases are used by ribosomes to form polypeptide chains
tRNA - carries amino acids to the ribosome
rRNA - ribosomal RNA molecules form part of the structure of ribosomes
Identify and define features of the genetic code.
- non-overlapping : each triplet is only read once
- degenerate: more than one triplet codes for the same amino acid.
- Universal = the same triplet codes for the same amino acid in all species
What is a locus?
- fixed position on a DNA molecule occupied by a gene
What is an allele?
- different versions of the same gene found at the same locus on a chromosome.
Define exons and introns
exons: Base/ triplet sequence coding for polypeptide/sequence of amino acids
Introns: regions of DNA that do not code for anything. ( non-coding DNA)
exons: regions of DNA that code for amino acid sequences
Where are introns found?
- between exons
- within genes
Describe how a gene is a code for the production of a polypeptide. Do not
include information about transcription or translation in your answer
- (Because) base/nucleotide sequence;
- (In) triplet(s);
- (Determines) order/sequence of amino acid /primary structure (in polypeptide);
Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (5)
give similarities also!!
- Nucleotide structure is identical;
- Nucleotides joined by phosphodiester bond;
- DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
Contrasts: - Eukaryotic DNA is longer;
- Eukaryotic DNA contain introns, prokaryotic DNA does not;
- Eukaryotic DNA is linear, prokaryotic DNA is circular;
- Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. (2) Give two reasons why.
- Triplets code for same amino acid
Accept: DNA/code/triplets are degenerate
Reject: codons (as question states within genes) - Occurs in introns /non-coding sequence;
Define the terms:
genome
proteome
genome: the complete set of genetic information contained in the cells of an organism
proteome: full) range of / number of different proteins that a cell is able to produce/ DNA is able
to code for (at a given time)
Describe the structure of mRNA.
- long , linear , single strand.
- It is made up of a sugar-phosphate backbone and exposed unpaired bases
- Uracil bases are present instead of thymine bases
Suggest the advantages of using mRNA rather than DNA for translation
- shorter & contains uracil so no excess polypeptide forms
- single-stranded & linear = ribosome moves along strand & tRNA binds to exposed bases
- contains no introns
Describe the structure of tRNA
- tRNA is a single-stranded molecule
- It has a sugar-phosphate backbone
- It has a folded , CLOVER LEAF shape
- has anticodon complemenrary to codon on MRNA
- has amino acid binding site
In a eukaryotic cell, the structure of the mRNA used in translation is different from the structure of the pre-mRNA produced by transcription.
Describe and explain a difference in the structure of these mRNA molecules.
- mRNA has fewer nucleotides
Pre-mRNA more nucleotides
OR
mRNA has no introns/has (only) exons
OR
Pre-mRNA has (exons and) introns; - (Because of) splicing
Accept mRNA is shorter OR pre-mRNA is longer
Describe how mRNA is formed by transcription in eukaryotes (5)
- Hydrogen bonds (between DNA bases) break;
- (Only) one DNA strand acts as a template;
- Free RNA nucleotides align by complementary base pairing;
- (In RNA) Uracil base pairs with adenine (on DNA)
- RNA polymerase joins (adjacent RNA) nucleotides;
- (By) phosphodiester bonds (between adjacent nucleotides);
- Pre-mRNA is spliced (to form mRNA by removing introns using enzyme splicesome
Describe how a polypeptide is formed by translation of mRNA (6)
- mRNA attaches) to ribosomes or RER ( ribosome moves to start codon)
- tRNA brings a specific amino acid;
- (tRNA) anticodons (bind to) complementary (mRNA) codons;
- Amino acids join by peptide bonds;
- (Amino acids join together) with the use of ATP; and peptidyl transferase enzyme
- tRNA released (after amino acid joined to polypeptide);
- The ribosome moves along the mRNA to form the polypeptide until stop codon is reached
peptidyl transferae
Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide.
Do not include descriptions of transcription and splicing in your answer
- mRNA associates with a ribosome / ribosome attaches to mRNA;
- Ribosome moves to / finds the start codon / AUG;
- tRNA brings / carries (appropriate / specific) amino acid;
- Anticodon (on tRNA complementary) to codon (on mRNA);
- Ribosome moves along to next codon;
- (Process repeated and) amino acids join by peptide bonds / condensation reaction (to form polypeptide);
using) ATP
Describe how mRNA is produced from an exposed template strand of DNA. Do not include DNA helicase or splicing in your answer
- (Free RNA) nucleotides form complementary base pairs
- Phosphodiester bonds form;
- By (action of) RNA polymerase;
Give the two types of molecules from which a ribosome is made (1)
- one of of RNA / ribonucleic acid / nucleotide/nucleic acid/rRNA / ribosomal RNA / ribosomal ribonucleic acid
and - one of protein(s) / polypeptide(s) / amino acid(s) / peptide(s) / ribosomal protein
rRNA + protein
Define mutation (1)
- ( random ) Change in the base/nucleotide (sequence of chromosomes/DNA);
- results in the formation of new allele
Explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual. (4)
no effect : ( any 2 of )
- Genetic code is degenerate (so amino acid sequence may not change);
- Mutation is in an intron (so amino acid sequence may not change);
- Does change amino acid but no effect on tertiary structure;
- (New allele) is recessive so does not influence phenotype;
positive effect :
- May result in increased reproductive success OR survival
- Results in change in polypeptide that positively changes its properties
degenerate : amino acids have more than one triplet/codon.
what is a substitution mutation?
- nucleotide in DNA sequence is replaced by another
- likely no change in the amino acid sequence
what is a deletion mutation?
- nucleotide is lost in the DNA sequence
- leads to a frame shift causing entire amino acid sequence to differ
Define mutagenic agent (2)
- A factor that) increases (the rate of) mutations;
- e.g. X rays , UV light , Gamma rays etc
What is a polyploidy chromosome mutation?
- where an individual has three of more sets of chromosmes instead of two
Describe chromosome non-disjunction
- occurs when chromosomes fail to separate during meiosis
- gametes may end up with one extra copy of a particular chromosome or no copies
e.g. DOWN’S SYNDROME
Genetic variation within a species is increased during meiosis by crossing over and the independent segregation of homologous chromosomes. Apart from mutation, explain one other way genetic variation within a species is increased. (2)
- Random fusion of gametes
OR
- random fertilisation - (Produces) new allele combinations
If most of the mitochondria in a cell are faulty, this prevents many important enzyme catalysed reactions taking place or slows them down.
Suggest and explain one reason why (2)
- not enough/ little ATP produced
- ATP provides energy for enzyme reactions
What is meiosis?
- a form of cell division that produces four genetically different haploid cells known as gametes ( sex cells)
Give 4 differences between mitosis and meiosis. (4)
- One division, two divisions in meiosis;
- (Daughter) cells genetically identical, daughter cells genetically different in
meiosis; - Two cells produced, (usually) four cells produced in meiosis;
- Diploid to diploid/haploid to haploid, diploid to haploid in meiosis;
- Separation of homologous chromosomes only in meiosis;
- Crossing over only in meiosis;
- Independent segregation only in meiosis;
Mitosis given first - then meiosis
Give difference between haploid and diploid (2)
- Haploid =single set of chromosomes, denoted as “n”. In humans, the haploid number of chromosomes is 23. GAMETES
- Diploid = having two sets of chromosomes, denoted as “2n”. In humans, the diploid number of chromosomes is 46. SOMATIC CELLS
Give the stages in Meiosis I
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
- same as mitosis except with crossing over
What is a bivalent?
- a pair of homologous chromosomes
Name the two sources of genetic diversity in meisois (2)
- crossing over
- independent assortment
Describe Prophase I
- DNA condenses into visible chromosomes
- Crossing over may occur at chiasma
- Centrioles migrate to opposite poles , spindle forms, nuclear envelope breaks
- Chromosomes consist of two sister chromatids joined by a centromere
Describe the process of crossing over and explain how it increases genetic diversity. (4)
- Homologous pairs of chromosomes come together + form a bivalent;
- Chiasma(ta) form;
- alleles are exchanged between non-sister chromatids
- Recombination occurs producing new combinations of alleles;
happens during prophase
Describe random assortment
also known as independent segregation
- occurs during metaphase I of meiosis
- Paired homologous chromosomes align randomly at the equator of the cell
- leading to random distribution of chromosomes into daughter cells
What happens during metaphase I?
- The bivalents line up along the equator of the spindle, with the spindle fibres attached to the centromeres
What happens during Anaphase I?
the sister chromatids separate and move to opposite ends of the cell
What happens during telophase I?
- spindle fibers start to break
- Nuclear envelopes form, nucleoli reform
- cytokinesis occurs after ( cell divides )
Describe the result of meiosis II.
meiosis II is the same as meiosis I just with half the number of chromosomes and chromatids.
- production of four haploid cells, each containing half the number of chromosomes compared to the original parent cell.
Explain how the chromosome number is halved during meiosis.
- Homologous chromosomes (pair);
- One of each (pair) goes to each (daughter) cell / to opposite poles;
Define population
- all the organisims of a particular species that live in the same place
Define genetic diversity.
- Differences in DNA / differences in base sequence of DNA
enables natural selection to occur
Name 4 processes that cause allele changes
- natural selection
- founder effect
- genetic drift
- bottleneck effect
what is a genetic bottleneck and its impact
- an event that causes a big reduction in a population
- reduces genetic diversity as it reduces the number of alleles in the gene pool
Define natural selection
- an increase in the number of beneficial alleles in a population due to a selection pressure.
- Selection pressures increase the chance of individuals with a specific phenotype surviving and reproducing over others
Describe the process of natural selection
1) individuals with beneficial allele more likely to survive, reproduce and pass on their genes.
2) greater proportion of the next generation inherits the beneficial allele
4) The frequency of the beneficial allele increases from generation to generation
5) Over generations this leads to evolution as the advantageous alleles become more common.
benefit of genetic diversity
- A population with a large gene pool or high genetic diversity has a strong ability to adapt to change
what is the founder effect and its impact on genetic diversity
- when only a small number of individuals from a large parent population start a new population
- thus there are only a small number of alleles in their initial gene pool
what is genetic drift
- gradual change in allele frequencies in a small population due to chance but not natural selection
Name three examples of selection pressures
Predation, competition and disease
What are the 3 types of adaptations?
describe them
Behavioural: changes to action to increase survival e.g. hibernation
Physiological: changes to bodily processes e.g. venom production
Anatomical: changes to body stucture e.g. thick layer of blubber
Name the 2 types of selection
Stabilising
Directional
Describe stabilising selection
Give and describe an example of stabilising selection
- human birth weights
- Very-low and very-high birth weights are selected against as they are less likely to survive
- leading to the maintenance of the intermediate birth weights
image : https://cdn.savemyexams.com/cdn-cgi/image/w=1920,f=auto/uploads/2021/03/Stabilising-selection-on-birth-weight.png
Describe directional selection?
- the extreme phenotype is favoured
- occurs when environmental conditions change
- individuals with phenotypes suited to the new conditions are favoured
image [https://cdn.savemyexams.com/cdn-cgi/image/w=1920,f=auto/uploads/2021/03/Directional-selection-antibiotic-resistance.png]
Give and describe an example of directional selection.
- antibiotic resistance
- antibioits is a selection pressure.
- Mutation occurs in bacteria that is resistant to antibiotic
- more likely to survive and reproduce
- over generations, this allele is favoured and leads to an increase in the frequency of the beneficial allele
define species
- a group of organisms that can interbreed to produce fertile offspring.
Define allopatric speciation .
- speciation that occurs when populations of the same species become geographically isolated from each other.
- thorugh geographic barriers such as mountains, rivers
- Isolated populations evolve independently, accumulating genetic differences over time.
Example: Galápagos finches
Describe sympatric speciation.
- Speciation that occurs within the same geographic area where the parent species is found.
- ## often due to factors like polyploidy, habitat differentiation, or behavioral changes.
[https://studymind.co.uk/notes/mechanism-of-natural-selection/?catid=19]
define speciation
formation of a new species e.g. through allopatric or sympatric speciaion
Compare and contrast allopatric and sympatric speciation (3)
- Allopatric speciation is slower than sympatric speciation
- Allopatric speciation takes place through geographical isolation whereas sympatric speciation does not
- Allopatric speciation occurs through natural selection whereas sympatric speciation occurs through polyploidy or beahvioural differences
What is courtship behaviour?
- behaviours such as visual , chemical or auditory stimuli that result in mating and reproduction.
what are the advantages of courtship behaviour?
- indivudals can recognise sexually mature members of their own speices of opposite sex
- syncronhise mating
- form a pair bond and sucessfully breed
Give three ways in which courtship behaviour increases the probability of successful mating (3)
- Recognise / identify / attract same species;
- Stimulates / synchronises mating / production / release of gametes;
- Recognition / attraction of mate / opposite sex;
Define classification
- the process of arranging organisms into groups
what is taxonomy?
- practice of biological classification
Name the 8 groups in the classification hierachy
largest to smallest
domain-kingdom-phylum-class-order-family-genus-species
each group is called a taxon
Name the three domains that organisms are first sorted into
Eukarya
Bacteria
Archaea : prokaryotes that thrive in extreme environments
what is the binomial naming system?
- The first name is the genus and
- The second name is the species
- The names are usually Latin
Homo sapiens
Homo - genus / sapiens = species
How are binomial names handwritten?
- first letter of generic name is capitalised , with rest being lowercased
- whole name must be underlined
What is phylogenetic classification?
- process of arranging organismis into groups based on their evolutionary origins and relationships
Name the techniques that are useful for clarifying evolutionary relationships
- Genome sequencing
- Comparing amino acid sequence
- Immunological comparisons
Explain how genome sequencing is useful for clarifying evolutionary relationships
- Advances in technology means that entire base sequences can be determined.
- The base sequence of one organism can then be compared to another to see how closely related they are
- Closely related species will have a higher percentage of similarity in their DNA base order
Explain how comparing amino acid sequences helps to clarify evolutionary relationships
- The sequence of amino acids in a protein is coded for by the base sequence in DNA.
- Related organisms have similar DNA sequences, and so similar amino acid sequences
- The more similar the sequence of cytochrome C, the more closely related they are
How can immunological comparisons help to clarify evolutionary relationships?
- An organism’s antibodies can be isolated and mixed with another organism’s proteins to see how many antigen-antibody complexes are formed.
- The more complexes that form, the more closely related the two organisms are.
Explain hierachical classification
- groups within groups
- no overlap between groups
Define biodiversity
- variety of living organisims
- can be measured through species diversity , ecosystem and genetic diversity
Define community.
- all the different species that live in one area and interact with one another
define species richness.
give a weakness
- number of species within a community
- can be misleadgin g, as it does not take into account the individuals of each species.
define index of diversity.
- describes the relationship between the number of species in a community and the number of individuals in each species.
How do you calculate index of diversity?
d = N ( N-1) / {n(n-1)
- the larger the number obtained , the higher the level of diversity.
N= total number of organisims of all species
n= total number of organisms each species
{ - sum of
what impact does farming have on species diversity?
- decreases species richness
- farmland is typically used for one species
- use of pesticides/ herbicides
what impact does farming have on genetic diversity?
- decreases
- farmers select for certain characteristics , which reduce number of different alleles in the population.
How can biodiversity be increased in areas of agriculture?
- use hedgerows instead of fences
- grow different crops around in the same area, or rotate crops around after a season
- limit use of pestricides and herbicides.
Name four ways we can compare genetic diversity between organismis.
- frequency of observale characteristics
- base sequence of DNA
- base sequence of mRNA
- Amino Acid Sequence
How is measurable and observing characteristcs used for dtermineg genetic diersity?
give limitation
- measurable : included number of legs , seeds , peetals , leaf indentations
- observable : colour , patters on fur etc , habitat
- not precise enough if only one characteristic is looked at
- simply inferring DNA differences throuch characteristcics of an organism is not reliable as could have external influences i.e environment
How is DNA sequencing used to determine genetic diversity?
- DNA is extracted from the nuclei of cells taken from an orgaism through skin samples or fossils.
- base sequences is obtained and compared to that of other organisms to determine evolutionary relationships.
- the more similarities in DNA base sequences , the more closely related members of diff species are
How is mRNA sequencing used to determine genetic diversity?
- often easier to isiolate from cells than DNA.
- mRNA can be used as a template to produce CDNA ( complemetary DNA.
icl dk what this is on about
How is amino acid sequencing analysis used to determine genetic diversity?
give limitation
- sequence of amino acids of the same protein can be compared ( must be found in all species being compared to e.g haemoglobin)
- evolves slower than DNA so may have same sequece but not as closely related as entailed.
what is meant by interspecific and intraspecific variation?
- interspecific : differences between indiviuals of different species
- intraspecific: differences between inndividuals of the same species
what is sampling?
- a method of investigating the abundance and distribution of species and populations.
- can be random or systematic
Give key differece betwee random and systematic sampling.
- in random sampling, positions of the sampling points are completely random or due to chance.
- this method is benefical because it means there will be no bias by the researcher.
- in systematic sampling , the positions of the sampling points are chosen by the person carrying out. There is a possibility of bias.
- when a sampling area is reasonably uniform, or has no clear pattern to the way the species are distributed then random sampling is favoured.
How are quadrats used in random sampling??
- create a grid for your sample area.
- use a random number generator to choose a set of coordiantes where the quadrat will be placed to remove bias
- calculate population density by counting number of indidvuals in each quadrat.
- use a running mean to get a representative sample.
- repeat until required sample size is reached
limitations of qudrats
- can only be used for sessile and immobile species ( plants and slowmoving animals)
- see save my exams
