genetic info, variation and relationships between organisms Flashcards
Gene
a section of DNA that contains a code for making a polypeptide and functional RNA
Locus
the location of a particular gene on a chromosome
Allele
a different version of the same gene
Eukaryotic DNA
- DNA is stored as chromosomes inside the nucleus
- linear chromosomes
- DNA is tightly coiled and wrapped around proteins called histones
Chromosome
composed of tightly coiled DNA wrapped around histones (if it is a eukaryotic cell)
Homologous chromosome
a pair of chromosomes that have the same genes therefore, they are the same size
Prokaryotic DNA
- DNA molecules are shorter and circular
- DNA is not wound around histones. Instead, it supercoils to fit in the cell
Codon
3 bases on mRNA that code for an amino acid
Start codon
3 bases at the start of an mRNA sequence which help to initiate translation
Stop codon
- 3 bases at the end of every gene that do not code for an amino acid
- this causes ribosomes to detach
- and therefore stops translation
What is meant by ‘the genetic code is degenerate?
each amino acid is coded for by more than one triplet of bases
Mutation
a change in the DNA
can be a gene or chromosome mutation
What is the advantage of the genetic code being non- overlapping?
if a point mutation occurs, it will only affect one codon and therefore one amino acid
What is the advantage of the genetic code being universal?
- genetic engineering is possible
- a human gene can be inserted into another organism
e.g human gene for insulin inserted into bacteria to make insulin
Genetic code
an amino acid is coded for by 3 DNA bases which are described as the “triplet code”
What is meant by ‘the genetic code is non-overlapping?
each base in a gene is only part of one triplet of bases that codes for one amino acid
therefore each codon is read as a discrete unit
What is the advantage of the genetic code being degenerate?
- if a substitution mutation occurs, the new triplet of bases may still code for the same amino acid
- therefore the mutation will have no impact on the final protein produced
Triplet code
an amino acid is coded for by 3 bases
What is meant by ‘the genetic code is universal?
the same triplet of bases codes for the same amino acid in all organisms
Introns
non-coding sequence of DNA
Exons
sequences of DNA that code for amino acids
What is splicing?
post-transcription modification
removing introns
Genome
the complete set of genes in a cell
Proteome
The full range of proteins that a cell is able to produce
Anticodon
3 bases on the tRNA which are complementary to the codon on mRNA.
mRNA structure
single-stranded
made up of codons a copy of one gene
tRNA structure
-single-stranded, folded to create a cloverleaf shape
-held in place by hydrogen bonds has an anticodon and amino acid binding site
mRNA function
- a copy of a gene from DNA
- created in the nucleus, and it
then leaves the nucleus - to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm
tRNA function
- a specific amino attaches at the binding site
- transfers this amino acid to the ribosome to create the polypeptide chain
Transcription
the first stage in protein synthesis
- one gene in DNA is copied into mRNA
- occurs in the nucleus
Translation
the second stage in protein synthesis
- the polypeptide chain is created using both the mRNA base sequence and the tRNA
- occurs on ribosomes in the cytoplasm
Which enzymes are involved in transcription?
DNA helicase
RNA polymerase
DNA helicase
catalyses the breaking of hydrogen bonds between the two strands of DNA
RNA polymerase
joins adjacent RNA nucleotides
together
forming a phosphodiester bond
pre-mRNA
mRNA in eukaryotes that still
contains the introns
How is pre- mRNA modified?
the introns are removed by a protein
- this leaves just the exons
What is ATP used for in translation?
forming the peptide bond between amino acids
Haploid
one copy of each chromosome in a cell
Diploid
two copies of each chromosome in a cell
Meiosis
- cell division that creates genetically different gametes
- there are two nuclear divisions in this process
- results in four haploid daughter cells
Independent segregation
- homologous pairs of chromosomes randomly line up opposite each other at the equator of the cell
- when they separate it creates a large number of possible combinations of chromosomes in the daughter cells produced
Crossing over
- homologous pairs of chromosomes line up opposite each other at the equator in meiosis 1
- parts of the chromatids twist, break and recombine with another chromatid
- results in new combinations of alleles in the gametes
Gametes
sex cells
How does meiosis introduce variation?
crossing over independent segregation
Types of gene mutations
deletion
substitution
What is a frameshift?
the removal of one base changes all of the subsequent codons
- all the bases shift back one position
Chromosome mutation
change in the number of chromosomes
occurs during meiosis
Deletion mutation
a gene mutation
a base is removed from a sequence
causes a frameshift
*
Substitution mutation
a gene mutation
a base is swapped for a different one
Non-disjunction
the chromosomes or chromatids do not split equally during anaphase
Polyploidy
changes in whole sets of chromosomes
e.g. when organisms have three or more sets of chromosomes
- mainly occurs in plants
Down’s syndrome
causes by a chromosome mutation
an example of aneuploidy
- 3 copies of chromosome 21
Aneuploidy
a change in the number of individual chromosomes
e.g 3 copies of chromosome 21
Genetic diversity
the number of different alleles in a population
Natural selection
the process that leads to evolution in populations
- results in species becoming better adapted to their environment
Allele frequency
the proportion of organisms within the population carrying a particular allele
Gene pool
all the genes and alleles in a population at a particular time
Evolution
the change in allele frequency over many generations in a population
Selection pressure
factors that affect the survival of an organism
the driving force of natural selection
Stabilising selection
- the middle (median) trait has a selective advantage and continues to be the most frequent in the population
- represented by a normal distribution graph
- range decreases as the extreme traits are lost over time
Directional selection
one of the extreme traits has a selective advantage
- occurs when there is a change in the environment
- the modal trait changes
Types of selection
stabilising, directional
An example of directional selection
antibiotic resistance
Binomial system
a universal naming system individuals are named after their genus and species
e.g. Homo sapiens
Phylogenetics
the study of species’ evolutionary origins and relationships
What is meant by a hierarchy?
smaller groups arranged within larger groups
there is also no overlap between groups
Importance of courtship
- helps to synchronise mating behaviour so that the animals are more likely to mate when the female is releasing eggs
- increases the likelihood of successful mating
- enables individuals to recognise members of the same species and opposite sex
Courtship behaviour
- different sequences of behaviours that animals demonstrate to attract a mate
- each species demonstrates its own unique behaviour
- essential for successful mating
species
a group of similar organisms that can breed to make fertile offspring
An example of stabilising selection
human birth weight
What are the taxa in the Linnaeus classification system?
domain kingdom phylum class order family genus species
Taxon
the term for each group in classification
Common ancestor
the species from which another species evolved
Species diverstity
the number of different species and the number of individuals within each species in a community
Species richness
the number of different species in a particular area at the same time
Index of diversity
- a measure of species diversity
- a calculation to measure the relationship between the number of species in a community and the number of individuals in each species
Community
all the species in a particular area at a particular time
Environment
the abiotic (non-living) factors in an area
Habitat
The range of physical, biological and environmental factors in which a species can live
How do you make sure your sampling is representative of the population?
take a large sample (at least 30)
randomly sample to avoid bias
Which farming techniques reduce biodiversity?
- destruction of hedgerows
- selective breeding
- monocultures
- over-grazing
- filling in ponds and draining wetlands
Biodiversity
- a measure of the range of habitats
- from a small local habitat to the entire Earth
- a measure of species diversity
- a measure of genetic diversity
How is standard deviation more useful than a mean?
it gives you the spread of data (variance) around the mean\
- overlaps in standard deviation indicate no significant difference in the means
How can you measure genetic diversity?
by comparing the base sequence of DNA, mRNA and the amino acid sequence of the proteins
Genetic diversity
the mesure of how many different alleles there are for each gene
Formula for Index of Diversity
D = N(N-1) / sum of n(n-1)
Compare the DNA in chloroplast/ mitochondria to prokaryotic DNA
the DNA is similar to prokaryotic DNA, in that it is:
* short
* circular
* not histone bound
How does transcription differ between prokaryotes and eukaryotes
- Transcription in prokaryotic organisms results in mRNA that requires no modification
- because prokaryotic DNA does not contain any introns
- eukaryotic transcription results in pre-mRNA that needs introns removed
What is the role of ribosomes in translation?
it holds two tRNA molecules to enable peptide bonds to form between the amino acids
What is the role of tRNA in translation?
it carries a specific amino acid anticodons align opposite complementary codons on the mRNA
Gene mutations
a change in the base sequence of DNA
substitution or deletion
When in the cell cycle do gene mutations occur?
interphase (s phase)
this is when DNA is replicated
