3.4 Genetic information, variation and relationships between organisms Flashcards Preview

AQA A level Biology > 3.4 Genetic information, variation and relationships between organisms > Flashcards

Flashcards in 3.4 Genetic information, variation and relationships between organisms Deck (83)
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3.4.1 DNA, genes and chromosomes

What is DNA? (2 points)

DeoxyriboseNucleic Acid


Compare Eukaryotic DNA with Prokaryotic DNA (4 points)

Eukaryotic DNA is large and long whereas prokaryotic is smaller and shorter as has less non coding DNA
Eukaryotic DNA is associated with proteins (histones) whereas Prokaryotic is not
Eukaryotic DNA is contained within the nucleus whereas prokaryotic DNA is not and is found free floating in cytoplasm so can mutate and replicate faster
Prokaryotic DNA is a single circular loop whereas eukaryotic found in linear chromosomes


What is a histone? (2 points)

A protein that DNA coils around to make a compact chromosome
Help to support the DNA


What is a chromosome? (1 point)

How DNA is stored in the nucleus


What are the features of chromosomes? (3 points)

23 pairs of chromosomes
Consist of maternal and paternal chromosomes
Cells that contain 23 pairs are diploid as have both sets of chromosomes


What is a homologous pair of chromosomes? (3 points)

Pairs of matching chromosomes
Both chromosomes are the same size and have the same genes, although they could have different alleles
Alleles coding for same characteristic will be found at same fixed position (loci) on each chromosome in homologous pair


What is a gene? (2 points)

A sequence of DNA bases that codes for either a polypeptide or functional RNA
Each gene is found at the same position (loci) on both the maternal and paternal chromosomes


What is an allele? (1 point)

A different version of a gene


What is the locus? (1 point)

The location of the gene on the chromosome


What is the genetic code? (1 point)

The sequence of base triplets (codons) in mRNA which code for a specific amino acid


What are the features of the genetic code? (4 points)

The code is a triplet code – one triplet (3 nucleotide bases) codes for one amino acid
The code is non-overlapping – base triplets don’t share their bases
The code is universal – each triplet code always codes for the same one amino acid
The code is degenerate – some amino acids are coded for by more than one triplet


How many possible triplets and amino acids exist? (2 points)

There are 64 possible triplets and 20 different amino acids


Why don’t all triplet codes result in amino acids? (2 points)

Some act as punctuation marks
Some indicate start and stop points for start/end of an amino acid chain (codons)


3.4.2 DNA and protein synthesis

What is transcription? (2 points)

The first stage of protein synthesis
The process by which pre-mRNA is formed


Describe the process of transcription (9 points)

Hydrogen bonds between two DNA strands in gene break due to DNA helicase, separating strands and DNA molecule uncoils exposing some of the bases
One of the strands is then used as a template to make mRNA copy
RNA polymerase lines up free RNA nucleotides alongside the exposed bases on template strand. Free bases are attracted to exposed bases
Complementary base pairing occurs between RNA nucleotides and DNA bases and are joined by RNA polymerase, forming mRNA molecule
RNA polymerase moves along DNA separating the strands and assembling mRNA strand
Hydrogen bonds between uncoiled strands of DNA reform once RNA polymerase has passed by and strands coil back into a double helix
When RNA polymerase reaches a stop signal, it stops making mRNA and detaches from DNA
mRNA moves out of nucleus through nuclear pore and attaches to ribosome for translation to take place


What happens before mRNA leaves the nucleus? (1 point)

- Introns (non-coding pieces of mRNA) are removed and functional exons (code for amino acids) are joined to form mRNA
- When introns included = pre-mRNA
- When introns removed = mRNA


What is translation? (2 points)

The second stage of protein synthesis
Process by which mRNA is used to make a specific polypeptide


Describe the process of translation (8 points)

The mRNA attaches itself to a ribosome and transfer RNA (tRNA) molecules carry amino acids to it. ATP provides energy for bond between amino acid and tRNA molecule to form
A tRNA molecule, with an anticodon that is complementary to the first codon on mRNA, attaches itself to the mRNA by specific base pairing
A second tRNA molecule attaches itself top next codon on mRNA in same way
The two amino acids attached to tRNA molecules are joined by a peptide bond
The first tRNA molecule moves away, leaving its amino acid behind
A third tRNA molecule binds to next codon on mRNA. Its amino acid binds to first two and second tRNA molecule moves away
Process continues producing a chain of linked amino acids (polypeptide chain) until there’s a stop signal on mRNA molecule
Polypeptide chain moves away from ribosome and translation is complete
Polypeptides join to form a protein


Describe the structure of a tRNA molecule (4 points)

tRNA is a single polynucleotide strand folded into a clover shape
Hydrogen bonds between specific base pairs hold the molecule in shape
It has a specific sequence of 3 bases at one end called anticodon
Have amino acid binding site at the other end


Describe the structure of mRNA (1 point)

Is a single polynucleotide strand


3.4.3 Genetic diversity can arise as a result of mutation or during meiosis

What is a mutation? (1 point)

A change in one or more nucleotide base or a change in sequence of bases in DNA


What are the three main ways of a mutation arising? (3 points)

Deletion – A nucleotide is lost from the DNA base sequence
Insertion – A nucleotide is added to the DNA sequence
Substitution – One nucleotide is replaced by another nucleotide with a different base


What effect does deletion and insertion have? (1 point)

Have greatest effect as cause change in whole sequence (frame shift – every amino acid after insertion/deletion will change)


What effect does substitution have? (1 point)

Only effects one amino acid but if degenerate code will have no effect


What is a chromosomal mutation? (1 point)

Changes in the structure or number of whole chromosomes


What are the two main types of chromosomal mutations? (2 points)

Polyploidy – occurs when organisms have 3 or more sets of chromosomes and occurs mainly in plants
Non-disjunction – Chromosomes fail to separate during meiosis


Compare mitosis and meiosis (5 points)

Mitosis produces cells for growth and repair whereas meiosis leads to production of gametes and ensures diversity in reproduction
Mitosis involves 1 cell division whereas meiosis involves 2
Mitosis produces 2 daughter cells whereas meiosis produces 4
In mitosis the daughter cells are diploid (two copies of every chromosome) whereas in meiosis the cells are haploid (only one copy of each)
In mitosis the daughter cells are identical to parent cells whereas in meiosis there is more variation as not identical


What is meiosis? (1 point)

The process by which a diploid nucleus (2n) divides to produce four haploid daughter nuclei (n)


Describe the process of meiosis (9 points)

Interphase - DNA unravels and replicates so there are two copies of each chromosome (chromatids)
Prophase 1 - Nuclear envelope breaks down and chromosomes condense
Metaphase 1 - Spindle fibres form and chromosomes line up along the equator
Anaphase 1 - Homologous chromosomes are pulled apart to opposite poles
Telophase 1 and cytokinesis - Two daughter cells are formed and cytoplasm divides
Prophase 2 - Two diploid daughter cells are produced, and nuclear envelope does not need to break down again
Metaphase 2 - Chromosomes line up along equator and attach to spindle fibres
Anaphase 2 - Sister chromatids are pulled apart to opposite poles
Telophase 2 and cytokinesis - Nuclear envelope reforms and four haploid cells are produced


How does meiosis lead to genetic diversity? (2 points)

Crossing over of chromatids – Crossing over of chromatids in meiosis 1 means that each of four daughter cells formed from meiosis contains chromosomes with different alleles
Independent segregation – Each homologous pair of chromosomes in cells is made up of one maternal chromosome and one paternal chromosome. When homologous pairs are separated in meiosis 1 its random which chromosome from each pair ends up in which daughter cell. So, four daughter cells produced have completely different combinations of maternal and paternal chromosomes which leads to genetic variation in offspring


3.4.4 Genetic diversity and adaptations

What is genetic diversity? (1 point)

The total number of different alleles in a population


How does genetic diversity lead to natural selection? (2 points)

Greater number of different alleles of a species, the greater the genetic diversity. The greater the genetic diversity, the more likely the species can adapt to environmental change which leads to natural selection


What increases genetic diversity? (2 points)

Mutations in the DNA which forms new alleles
Gene Flow - different alleles being introduced into a population when individuals from another population migrate into them and reproduce


What is natural selection? (1 point)

The differential survival and reproduction of individuals due to differences in their phenotype


How does natural selection work? (5 points)

A mutation occurs creating a new allele
Individuals that have an advantageous allele that increases their chance of survival are more likely to survive, reproduce and pass on the beneficial allele
This means greater proportion of next generation inherits beneficial allele
So, they are more likely to survive, reproduce and pass on their genes
The new allele increases in frequency in the population


What are the three types of adaptations in natural selection? (3 points)

1. Anatomical – appearance e.g. shorter ears and thicker fur in Arctic foxes
2. Physiological – chemical reactions/processes internally e.g. oxidizing of fat rather than carbohydrates to produce extra water for camels
3. Behavioural – Actions of the organism e.g. migration of swallows from UK to Africa to escape cold in winter


What is a phenotype? (1 point)

An observable physical characteristic that organisms have


What is a genotype? (1 point)

Genetic make-up of an organism


What is the gene pool? (1 point)

Total number of alleles in a population at a specific time


What is allele frequency? (1 point)

The number of times an allele occurs within the gene pool - % of all chromosomes in a population that carry that allele


What is selection? (1 point)

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


What are the two ways in which natural selection affects the normal distribution curve? (2 points)

Directional selection
Stabilising selection


What is directional selection? (6 points)

Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce

Mutations result in increased genetic diversity
Change in the environment occurs
Selection favours individuals that vary in one direction from the mean
The mean characteristic of the population changes
Phenotypes of one extreme in the population is selected for


What is stabilising selection? (5 points)

Where individuals with alleles for characteristics towards middle of range are more likely to survive and reproduce

Mean phenotype is favoured
Extreme phenotypes are selected against
Environment is stable
Number of individuals with that trait increases


Compare directional and stabilising selection (3 points)

Directional selection selects extreme phenotype whereas stabilising selects mean
Directional changes the characteristics of the population whereas stabilising preserves them
Directional makes curve keep same shape but shifts mean to left or right whereas stabilising curve becomes narrower and higher, but mean doesn’t change


Practical – aseptic techniques



3.4.5 Species and taxonomy

What are courtship displays (behavioural adaptation)? (1 point and 3 examples)

A set of behaviours in which an animal attempts to attract a mate and exhibit their desire to copulate
e.g. vocalizations, displays of beauty or strength, ritualised movements (dances)


How do courtship signals work in stimulus response chains? (5 points)

Male communicates a courtship signal
This acts as visual stimulus to females
Females nervous system detects and if receptive responds to stimulus with a specific innate of her own
This acts as stimulus to male
The male responds


Why are courtship displays important? (4 points)

1. Enables members to recognise their own species to prevent crossbreeding/infertile offspring
2. Allows animal to identify a mate that is capable of breeding
3. Helps form pair bonds to lead to successful breeding and raising of offspring
4. Helps synchronise mating seasons to ensure maximum chance of fertilisation


What is classification? (1 point)

The organisation of living organisms into groups


What is taxonomy? (1 point)

The theory and practice of biological classification


What are the two forms of classification? (2 points)

Artificial classification
Phylogenetic classification


What is artificial classification? (2 points and 3 examples)

Based on analogous characteristics (characteristics that have the same function but not same evolutionary origin)
Not based on evolutionary relationships
E.g. colour of flowers, size, having wings


What is phylogenetic classification? (4 points)

Classifies species based on shared features derived from ancestors
Based on evolutionary relationships between organism and ancestor
Partly based on homologous characteristics
Arranges groups of organisms into a hierarchy


What is the classification hierarchy (binomial system)? (9 points)

Kingdom King
Phylum Phillip
Class Came
Order Over
Family From
Genus Great
Species Spain


What are the features of the hierarchy? (5 points)

Broadest at top and most specific at bottom
Smaller groups within larger groups
No overlap
Each group is called a taxon (taxa)
Based on their ancestry/evolutionary relationship


What is a species? (1 point)

A group of similar organisms able to reproduce to give fertile offspring


How does a species get its scientific name? (2 points)

First name comes from the Genus (upper case first letter)
Second name comes from the Species (lower case)


What are the three domains? (3 points)

Domain is the highest taxonomic rank
- Bacteria
- Eukarya
- Archaea


What are the features of bacteria? (7 points)

Single celled prokaryotes with following features:
- No membrane bound organelles
- Unicellular (some cells may occur in chains or clusters)
- Cell walls made of murein
- Single loop of naked DNA made up of nucleic acids but not associated with histones
- Smaller ribosomes 70s
- Some may cause disease
- Important decomposers in environment as breaks down dead organisms


What are the features of eukarya? (6 points)

- Membrane bound organelle such as nucleus
- Not all possess cells with cell walls e.g. animals
- If cell walls present, made of cellulose
- Ribosomes are larger 80s
- DNA is associated with proteins
- Split into 4 kingdoms: Protoctista, fungi, plantae, animalia


What are the features of archaea? (5 points)

- Single celled prokaryotes
- Similar shape and size to bacteria
- Genes and protein synthesis similar to eukaryotes
- No murein in cell walls
- More complex form of RNA polymerase for transcription and translation


3.4.7 Investigating biodiversity

What are the features of phylogenetic trees? (2 points)

Most recent representatives at end of branches
Oldest ancestor species at base of tree


What was the original classification method? (1 point)

Observable characteristics – changes in evolutionary features must have been mirrored by changes in proteins and therefore DNA


What are the positives and negatives of using observation features? (3 positives and 5 negatives)

+ Easier as anyone can do it
+ Cheaper as does not require and advanced equipment
+ Easier to observe

- Patterns of inheritance not always clear
- Differences are often discrete so interpretation subjective
- If using fossil data, it might be hard to find
- Most genes are polygenic
- May be a result of similar environments not similar evolutionary history


What is the modern classification method? (2 points)

Can get more accurate definition of a species by comparing:
1. DNA base sequences/mRNA sequences
- comparing the exact order of nucleotides on the DNA to determine how diverse organisms are or spot where mutation and therefore new species occurred
- mRNA is complementary to DNA
- BUT, can cost a lot and take a while to complete

2. Amino acid sequence in proteins
- Determined by the DNA or mRNA
- Similarity of amino acid sequence = similarity of species
- BUT, can cost a lot, take a while to complete and some DNA will be non-coding/non functional


Describe how the process of DNA hybridisation can allow studying genetic diversity (4 points)

Heat both organism A and B to separate strands of DNA by breaking hydrogen bonds
Combine single strands of DNA from both organisms
Cool to allow renaturation of double-stranded DNA (hydrogen bonds reform)
Determine degree of hybridisation
(Complete hybridisation = all bonds form between strands so organisms identical)
(Partial hybridisation = Some bonds reform but others don’t so organisms are related)
(No hybridisation = No bonds formed so organisms are unrelated)


How can we tell how many hydrogen bonds formed during DNA hybridisation? (3 points)

Increase temperature again
Record temperature required to separate two strands
Higher temp required = greater number of hydrogen bonds formed = greater similarity in DNA = Closer related species are


How can we use immunology to study genetic diversity? (5 points)

Serum containing human antigens is injected into another species (usually rabbits as easier to keep in lab)
Rabbits immune system makes anti-human antibodies which are collected
Antihuman antibodies are mixed with serum from other species
The more similar the species is to the human, the more antibody-antigen complexes formed
Precipitate forms when antibody-antigen complexes are formed. The more precipitate, the closer the evolutionary relationship


3.4.6 Biodiversity within a community

What is species diversity? (1 point)

The number of different species AND the number of individuals of each species within any one community


What is genetic diversity? (1 point)

The variety of genes possessed by the individuals that make up any one species


What is ecosystem diversity? (1 point)

The range of different habitats within a particular area


What was the previous method of calculating species diversity? (1 point and 1 problem)

Species Richness – Number of different species in a particular area at one time
PROBLEM: Doesn’t consider number of individuals of each species


What is the calculation for species diversity index?

d= sum of n(n-1)

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


How have humans caused a reduction in biodiversity?

Agriculture (demand for food has more than doubled)
Used land for home and industry
Production of fossil fuels

These factors have had direct impact on species diversity, genetic diversity, ecosystem diversity and therefore the whole food web


What problems have agriculture caused?

Monoculture (growing only one species)
- Reduction in species and genetic diversity both directly and indirectly
Lack of intercropping (rotating what is grown each season)
- Drains the soil of its nutrients which results in monoculture
Competition for space
- Natural species/habitats cannot grow as are outcompeted
Use of pesticides and fertilisers
- Kills species as can be toxic and enter water cycle causing eutrophication
- Overgrazing and trampling causes a reduction in species diversity and habitats
Draining wetland and marshes
- Removes nutrients and moisture from soil so species cannot grow
Removing hedgerows
- Destroys habitats and food sources


What effect does deforestation have?

Deforestation is the permanent clearing of forests and the conservation of land for other uses such as agriculture, grazing or settlement
Leads to a loss of species, reduction in habitats, reduction in food sources, reduction in decay so soil nutrients decrease and reduction in species diversity index


How does reduction in biodiversity affect variation?

A reduction in biodiversity can directly affect the phenotypic and genetic variation present
Two types of variation that may result:
- Intraspecific (variation WITHIN a species)
- Interspecific (variation BETWEEN species)


What are the quantitative methods of studying variation?

When using these methods, they cannot take a single measurement as may be unreliable, unrepresentative and not trustworthy


What is sampling bias and how can it be overcome?

Choices made by investigator are biased and sample unrepresentative deliberately or unwillingly
Avoided by using random sampling


What is chance variation and how can it be avoided?

Even if bias is avoided, sample may be unrepresentative as all individuals are the same
Avoided using data analysis and increasing sample size


What is standard deviation?

Determines the extent to which chance may have influenced the data by measuring how far the data deviates from the mean
The closer to the mean the values are, the more probable we can be that our results are correct
A measure of the width of the curve on a normal distribution curve
Indicates the range of values either side of the mean
The distance from the mean until the curve changes from convex to concave


Steps to calculate standard deviation

1. Calculate mean
2. Subtract mean from each of individual values
3. Square the values (ensure no negatives)
4. Add all squared numbers together
5. Add number of values and minus 1
6. Sqare root some of square values divided by number of values minus 1