3.4 Genetic information, variation and relationships between organisms Flashcards
3.4.1 DNA, Genes and Chromosomes
How is DNA associated in prokaryotic cells?
- DNA is short
- DNA is circular
- DNA is not associated with proteins
How is DNA associated in eukaryotic cells?
- found in the nucleus
- DNA molecules are very long
- DNA is linear
- DNA is associated with proteins, called histones.
What do DNA molecules and its associated proteins form?
- A chromosome
What other subcellular structures in a eukaryotic cell contain DNA and how is it associated in these structures?
- chloroplasts
- mitochondria
- the DNA is associated like the DNA in a prokaryotic cell; short, circular and not associated with proteins
What is a gene?
- A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide and a functional RNA
What is a locus?
- when gene occupies a fixed position on a particular DNA molecule.
What is a triplet?
- A sequence of three DNA bases which codes for a
specific amino acid.
Give three features of the genetic code
- universal
- non-overlapping
- degenerate.
What is meant by ‘universal’?
- all species use the same four bases A,T,C and G
- each base sequence codes for the same amino acid in all species
What is meant by ‘non-overlapping’?
- each triplet is only read once
- triplets don’t share any bases.
What is meant by ‘degenerate’?
- more than one triplet codes for the same
amino acid - this reduces the number of mutations
What are exons?
- A sequence of DNA that codes for an amino acid sequence.
What are introns?
- non-coding regions of the gene
- do not contain codons needed to make the final protein
- Introns are found in between exons.
3.4.2 DNA and Protein Synthesis
Define the term ‘genome’
- the complete set of genes in a cell
Define the term ‘proteome’
- the full range of proteins that a cell is able to produce.
What is RNA made up of?
- RNA nucleotides are ribose
- a phosphate group
- and one of the four bases adenine, cytosine, guanine or uracil
Describe the structure of RNA
- Contains pentose sugar ribose
- it is single stranded
- Contains uracil instead of thymine
- is a relatively short polynucleotide chain.
What is DNA made up of?
- DNA nucleotides are deoxyribose
- a phosphate group
- one of the organic bases adenine, cytosine, guanine or thymine.
Describe the structure of DNA?
- contains pentose sugar deoxyribose
- is double stranded
- thymine paired with adenine
- long
- double helix composed of two polynucleotides joined together by a hydrogen bonds
Describe the structure of tRNA
- small molecule made up of around 80 nucleotides.
- It is single stranded
- folded into a clover leaf shape in which one end extends from the others. (here an amino acids
attaches). - At the opposite end is an anticodon which is specific to the amino acid that the tRNA attaches to.
Describe the structure of mRNA
- this is a long single strand
- created during transcription
- the base sequence is complementary to DNA.
- Each set of three bases, called the codon, match a triplet on the DNA as well as the tRNA.
Describe the process of transcription
- The DNA helix unwinds to expose the bases to acts as a template
- Only one chain of the DNA acts as a template
- This unwinding an unzipping is catalysed by DNA helicase
- DNA helicase breaks the hydrogen bonds between bases
- Free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases
- The enzyme RNA polymerase joins together the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied
- Once copied, the mRNA is modified and then leaves the nucleus through the nucleur envelope pores
In prokaryotes, what does transcription result in the production of?
- transcription results directly in the production of mRNA from DNA.
In eukaryotes, what does transcription result in the production of?
- results in the production of premRNA;
- this is then spliced to form mRNA.
What happens during translation?
- amino acids join together to form a polypeptide chain
Describe the process of translation
- mRNA attaches to a ribosome and tRNA collects amino acids from the cytoplasm and carries them to the ribosome. tRNA is a single stranded molecule with a binding site at one end thus it can only carry one type of amino acid, and a triplet of bases (anticodon) at the other.
- tRNA attaches itself to mRNA by complementary base pairing – two molecules attach to mRNA at a time
- The amino acids attached to two tRNA molecules join by a peptide bond and then tRNA molecules detach themselves from the amino acids, leaving them behind.
- This process is repeated thus leading to the formation of a polypeptide chain until a stop codon is reached on mRNA and endsthe process of protein synthesis
3.4.3 Genetic diversity arise as a result of mutation/during meiosis
What are gene mutations?
- Gene mutations involve a change in the base sequence of chromosomes/DNA
- They can arise spontaneously during DNA replication
What are the two key types of mutation?
- Base deletion
- Base substitution
What is base substitution?
- is when one nucleotide in the DNA sequence is replaced by another.
- Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids.
What is base deletion?
- is when a nucleotide in the DNA sequence is lost.
- The loss of a single nucleotide can have a significant impact as it leads to a frame shift, resulting in completely different amino acids being coded for.
How is the mutation rate increased?
- by mutagenic agents
What are the two forms of mutation in chromosomes?
- polyploidy
- non-disjunction
What is polyploidy?
- Changes that occur in whole sets of chromosomes
- An individual will end up with three of more chromosomes instead of two
What is non-disjunction?
- occurs when chromosomes fail to separate correctly in meiosis
- the gametes and zygotes formed will have one more or one less chromosome than they should
- down syndrome is the result of non-disjunction where individuals have an extra chromosome 21
What is meiosis?
- Meiosis is a form of cell division that results in production of four genetically
different daughter cells - they have half the number of chromosomes found in the parent cell
What is the main role of meiosis?
- the main role of meiosis is the production of haploid gametes as cells produced by meiosis have half the number of chromosomes.
-This is necessary to maintain a stable number of chromosomes.
How can genetic variation be achieved?
- independent segregation of homologous chromosomes
- crossing over of homologous chromosomes
What is independent segregation of homologous chromosomes?
- there are various combinations of chromosome arrangement
- during meiosis 1 homologous chromosomes line up in pairs, the arrangement of these pairs is random, meaning that the division into the daughter cells is also random.
What is crossing over of homologous chromosomes?
- When pairs of chromosomes line up they can exchange some of their genetic material.
- Crossing over occurs when one chromosome may swap places with the same part of its homologous pair leading to a different combination of alleles on the gene.
Describe the stages of meiosis
- two nuclear divisions result usually in the formation of four haploid daughter cells from a single diploid parent cell
- Meiosis 1 - homologous chromosomes pair up whereby crossing over at the chiasmata may take place. The cell then divides whereby each daughter cell contains one chromosome from each homologous pair.
- Meiosis 2 - the chromatids of each chromosome are separated producing 4 haploid daughter cells.
****3.4.4 Genetic diversity and adaptation**
What is genetic diversity?
- the number of different alleles of genes in a
population. - it is a factor that allows natural selection to occur
Define population
- is
defined as a group of individuals of the same species that live in the same place and are able to
breed with one another.
Define species
- Consists of more than one population
What is the impact of lots of alleles in a population?
- The greater the number
of alleles in a population the greater the genetic diversity, and therefore the greater the chance
that a population would survive a change in their habitat.
What is meant by the niche of a species?
- is its role within the environment
- species which share the same niche compete with each other
What is natural selection?
- the idea that better adapted species survive
- it is the process in which the fitter individuals who are better adapted to the environment survive and pass on the advantageous genes to future generations
What is evolution?
- the process by which the frequency of alleles in a gene pool changes over time as a result of natural selection
What are the principles of natural selection in the evolution of populations?
- Random mutations can result in new alleles of a gene
- Many mutations are harmful but in certain environments the new allele of a gene might benefit its possessor, leading to increased reproductive success
- 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. - this leads to evolution
What is selection?
- Selection is the process by which individuals that are better adapted to their environment are
more likely to survive and breed. - This means that they can pass on their advantageous alleles.
- Every living organism is subject to selection determined by the conditions which they are living
in.
What are the two key types of selection?
- directional selection
- stabilising selection
What is directional selection?
- directional selection occurs when the environmental conditions change and the phenotypes best suited to the new conditions are more likely to survive.
- As a result these individuals will breed and produce offspring.
- Overtime the mean of the population will move in the direction of these individuals.
Give and example of directional selection
- bacteria being resistant to antibiotics.
- A single bacteria will have had a mutation that meant it was not killed by penicillin as it could produce the enzyme penicillinase.
- As a result it was able to grow and populate, and the frequency of the allele that enabled penicillinase production increased in the population.
-Therefore the population moved to have greater penicillin resistance.
What is stabilising selection?
- In stabilising selection the phenotypes with successful characteristics are preserved and those of greater diversity are reduced.
- This selection doesn’t occur due to changes in the environment.
- If the environment stays the same then the individuals closest to the mean are favoured because they have the alleles that have given them the survival
advantage.
-The furthest from the mean are selected against.
Give an example of stabilising selection?
-An example is new born babies weights.
-Those that have a birth weight of around 3kg are more likely to survive than those at the extremes
How are organisms adapted to their environment as a result of natural selection?
- Anatomical adaptations are physical adaptations, either external or internal
- Behavioural adaptations are changes in behaviour which improve the organism’s chance of survival e.g. mating calls.
- Physiological adaptations are processes inside an organism’s body that increase its chance of survival e.g. regulation of blood flow through the skin.
3.4.5 Species and taxonomy
How do two organisms belong to the same species?
- if they produce fertile offspring
How can we identify organisms?
- Each species is universally identified by a binomial consisting of
the name of its genus and species, eg, Homo sapiens
What is the generic name?
- the first name is the genus which the organism belongs to
- if a species is closely related it will snare the same genus
What is the specific name?
- it is the species to which the organism belongs to
What is courtship behaviour?
- used for members of the same species to recognise one another during mating
- members of the same species have similar physical, biochemical and behavioural characteristics
- courship behaviour takes place before mating
What is the importance of courtship behaviour?
it is a necessary prescursor for successful mating as it enables individuals to:
* recognise members of their own species
* synchronise mating
* form a pair bond
* become able to breed
What is classification?
- the process of naming and organising organisms into groups based on their characteristics
What are the 5 kingdoms organisms can be placed into?
- Animals
- Plants
- Fungi
- Prokaryotes
- Protists
What is the order of the hierarchal structure?
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
- It makes smaller groups be placed within larger groups
What is phylogenetic classification?
- A phylogenetic classification system attempts to arrange species
into groups based on their evolutionary origins and relationships.
What are the 3 domains organisms can be separated into?
- Bacteria
- Archea
- Fung
How does the scientific community evaluatetne data given?
- the findings are published in scientific journals and presented in scientific conferences
- Scientists then study the evidence in a process called peer review
- Scientists start collecting evidence to either support or reject the suggestion
How have changes over time allowed scientists to help clarify relationships between organisms?
- advances in
immunology and genome sequencing help to clarify evolutionary
relationships between organisms
3.4.6 Biodiversity within a community
What is biodiversity and how can it be measured?
- the variety of living organisms there are
- it can relate to a range of habitats, from a small local habitat to the earth
- can be measured in terms of species diversity, genetic diversity and ecosystem diversity as well as index diversity
What is species diversity and how can it be measured?
- the number of different species and the number of different individuals in a community (also known as species richness)
- can be measured by simply counting the number of species present e.g. random sampling
What is genetic diversity?
- it is a measure of the genetic variation found in a particular species
- the number of different alleles in a gene pool
What is ecosystem diversity?
- it is the range of different habitats
What is the index diversity and how can it be calculated?
- describes the relationship between the
number of species in a community and the number of individuals in
each species. - Calculation of an index of diversity formula
- d =
N (N − 1)
Σn (n − 1) - D= diversity index
- N = total number of organisms of ALL species
- n = total number of organisms of EACH species.
- Σ= the sum of
What are the impacts of agriculture on biodiversity?
- Farming techniques reduce biodiversity and the number of species present because humans select for particular characteristics.
- This therefore reduces the number of alleles
and the genetic diversity of the population.
-Farmland is typically used for only a single species and therefore means that fewer individuals of other species can survive there
What are some techniques farmers use order to maintain biodiversity?
- Using hedgerows instead of fences.
- Growing different crops in the same area, known as intercropping.
- Reducing the use of herbicides and pesticides.
- Preserving wetlands instead of draining these for farming use
3.4.7 Investigating diversity
How can genetic diversity between species be determined?
- Genetic diversity within, or between species, can be made 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 and mRNA
Wnat are the limitations of comparing observable characteristics (like the shape or size of a head), have on classifying species
- the characteristics could be coded for by more than one gene
- the same characteristics may have arisen seperately
- the characteristics could be influenced by the environment and not the genes
How can base sequences of DNA and in the amino acid sequences of proteins suggest relationships between different organisms within a species and between species
- The sequence of amino acids can also be studied as this can be taken back to the mRNA sequence and thus the DNA sequence.
- Can use intraspecific and interspecific variation
What is interspecific variation?
The differences between species are called interspecific variation.
What is intraspecific variation?
- differences between individuals of the same species
What methods do scientists now use to investigate genetic diversity?
- gene technology to read the base sequences of organisms
- it has caused a change in the methods of investigating genetic diversity
- DNA
differences from measurable or observable characteristics
has been replaced by direct investigation of DNA sequences
What are some quantitative investigations of variation within a species?
- collecting data from random samples
- calculating a mean value of the collected data and the
standard deviation of that mean - interpreting mean values and their standard deviations.
What is sampling?
-Sampling is the random selection of individuals to measure characteristics is species however it may not be representative of the population due to chance and sampling bias.
How do we eliminate sampling bias and increase the reliability of our results?
- To eliminate sampling bias a quadrat or transect can be used by placing these on randomly generated coordinates in the sample area.
- To increase the reliability of the results a larger sample size is needed.
