DNA And Genes Flashcards
What is the DNA like in a eukaryotic cell?
They have most of their DNA in the nucleus. This DNA is linear, as chromosomes
Structure of chromosomes
Each chromosome is a length of double stranded DNA wrapped around his tone proteins
What is the complex of DNA and protein called
Chromatin
Where is most of our DNA found
It’s not found in genes but makes up promoter regions and multiple repeat regions between genes
What are introns
Non-coding and found within genes
What are exons
Coding
What happens to introns during protein-synthesis?
They are spliced out
What is the DNA like in prokaryotic cells?
It’s circular,not associated with histones and dos not contain introns
The structure of DNA in mitochondria and chloroplast?
It’s prokaryotic in nature (circular, no histone proteins, no introns)
What does each gene code for?
Either polypeptide of a functional RNA molecule (e.g. tRNA or rRNA)
How can genes be switched on and off?
Using the promotor regions and methylation/acetylation
Definition of a genome
All of the DNA present in a cell or organism
What’s different about stop(TAA,TAG,TGA)
ends every genetic code
Definition of a proteome
All of the proteins that a cell is able to synthesise
Features of the genetic code
- universal, it’s the same in all living organisms
- non overlapping , each nucleotide is only read once
- degenerate, more than 1 code (codon) for many amino acids
What’s different about methyanine (ATG)
starts the universal code for every gene
What are the two stages of protein synthesis
- transcription
- translation
What happens at the start of transcription?
Breaking of hydrogen bonds between the strands of the gene at the locus (position of interest). This exposes the base on the template strand. Free nucleotides bind to their complementary DNA base
What does RNA polymerase form in transcription?
Phosphodiester bonds between adjacent RNA nucleotides. This forms premrna . This goes to a spliceosome where the introns are spliced out and the produces mRNA. This travels out the nucleus via a nuclear pore and is taken to a ribosome
What happens during translation
- In the ribosomes each codon (sequence of amino acids) is “read” and a complementary tRNA molecule is attached
- The ribosome catalyses the formation of peptide bonds between adjacent amino acids using energy from ATP
- Once the amino acid joins the polypeptide the tRNA molecule leaves the ribosomes to gain another specific amino acid
4.when a stop codon is reached the process of translation stops - Polypeptide folds into the tertiary structure
what are the two keys types of mutationin a DNA sequence:
- substitution
- deletion
what is a substitution mutation?
when one nucleotide in the DNA sequence is replaced by another. Substitution may not be harmful as the substituted nucleotide may code for the same amino acid.
what is a deletion mutation?
when a nucleotide in the DNA sequence is lost. This results in different amino acids being coded.
what Mutations can occur in chromosomes:
- polyploidy
- non-disjunction
what is polyploidy mutation in chromosomes?
an individual has 3 or more sets of chromosomes instead of 2. This is common in plants, with many modern wheats
what is Non-disjunction mutation in chromosomes?
occurs when chromosomes fail to separate correctly in
meiosis. gametes and zygotes formed will have 1 more/less chromosome than they should. Down’s syndrome is an example of this where individuals have an extra chromosome 21.
what is meiosis
form of cell division that gives four daughter cells that are genetically different and have half the number of chromosomes found in the parent cell.
what is the main role of meiosis?
the production of haploid gametes. as cells produced by meiosis have half the number of chromosomes. This maintains a stable number of chromosomes.
genetic variation is achieved through in cells?
- Independent assortment of chromosomes
- Crossing over of chromatids
what is the Independent assortment of chromosomes?
various combinations of chromosome arrangement. in meiosis 1 homologous chromosomes line up in pairs,the pair arrangement is random, meaning that the division into the daughter cells is random.
what is Crossing over of chromatids
chromosome swaps places with the same part of its homologous pair leading to a different combo of alleles on the gene.
pairs of chromosomes line up they exchange some genetic material.
chiasmata forms
what are the Stages of Meiosis?
its split into tow nuclear divisions
- meiosis 1
- meiosis 2
what happens in meiosis 1
homologous chromosomes pair up they cross over at the chiasmata. cell divides, each daughter cell contains one chromosome from each homologous pair.
what happens in meiosis 2
the chromatids of each chromosome are separated producing 4 haploid daughter cells.
What is genetic diversity
Number of different alleles of genes in a species or population
What is a population?
The number of organisms of the same species in the same area at the same time that are able to interbreed
How can genetic diversity be increased?
mutations and gene flow (migration)
Why is high genetic diversity beneficial to a population?
As it’s a factor, enabling natural selection to occur
What is the process of natural selection?
- Random mutation results in a new allele for a gene
- The new allele increases the chance of survival for that individual so its more likely to reproduce
- Advantageous allele is inherited by members of the next generation.
- Over many generations, the frequency of the new allele increases.
What does natural selection result in?
Species that are better adapted to their environment
Three Types of adaptations
- anatomical (physical structure)
- Behavioural, (e.g. hibernation)
- Physiological (e.g. Secrete, poisons/toxins)
What are the three main forms of selection?
- Directional selection
- Stabilising selection
- Disruptive selection
Describe how the production of messenger RNA (mRNA) in a eukaryote cell is different from the production of mRNA in a prokaryote cell.
- pre mRNA only produced in a eukaryotic cell
- splicing only occurs in a eukaryotic cell
- introns removed in eukaryotic cell
Give two differences between the structure of mRNA and the structure of tRNA
- mRNA is longer/ has more nucleotides
- mRNA contains no hydrogen bodns and tRNA does
The genetic code is described as being degenerate. What does this mean?
An amino acid can be coded for by more than one triplet
What is a codon?
- triplet of bases on mRNA
- that code for an amino acid
Define the term exon.
Nucleotide sequence coding for a sequence of amino acids
In a eukaryotic cell, the base sequence of the mRNA might be different from the sequence of the pre-mRNA.
- introns in premrna
- splicing
start codon?
methionine
why do introns have to be spliced out?
prevent the synthesis of a polypeptide if they weren’t spliced out
what is the diploid number
full set of chromosomes
what is recombination
broken-off portions of chromatid combine with another chromatid
what is genetic recombination by crossing over
- the chromatids of each pair becomes twisted around one another
- chromatids break off
- broken portions re-join with the chromatids of its homologous partner
2n
where n= the number of pairs of homologous chromosomes
What is a species?
A group of similar organisms that are able to breed and produce fertile offspring
What is a binomial name?
Each species has one of these. They consist of two internationally recognised names, the genus (or generic) and the species (or specific)
Humans binomial name
Homo sapiens
Why are courtship behaviours essential?
- when species look similar
- recognise mmebers of thier own species
- identify a mate that is capable of breeding
- form a pair bond
- snychronise mating
- breeding
What are courtship rituals?
When members of the same species will recognise each other, as they will do,and respond to the same rituals
Examples of courtship rituals:
- Sounds - mating call common in birds
- Visual displays- the tail display of a male peacock
Effect of courtship behaviour on species?
The more closely related the courtship behaviour the more closely related the species are
What are the eight phylogenetic classification?
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
What does phylogenetic classification produce?
Hierarchy where groups are contained within larger groups with no overlap
What is each group called in the phylogenetic classification?
Each group in a hierarchy is called taxon - classification has eight taxa
Artificial classification
Classification can be artificial, e.g. size, colour, number of legs
These are analogous - they have the same function, but different evolutionary origins
Phylogenetic classification
This is based on evolutionary history
These are homologous - they have similar evolutionary origins, regardless of their functions. Commonly referred to as ancestral - showing a common ancestor
What has altered long-held beliefs of classification?
Modern advances in immunological and sequencing techniques
What are the methods of classification?
- DNA/amino acid sequencing
- DNA hybridisation
- Immunological comparisons
What does DNA/amino acid sequencing provide?
provides data that can be compared, the more closely related species the more similar the sequence is.
What happens in DNA hybridisation?
The more corresponding bases found in a gene of two species, the more hydrogen bonds will form when they are mixed together.
The higher the temperature required to break the bonds, the more complimentary bases there are so the closer the species are related.
What happens in immunological comparisons?
inject a protein into a rabbit to raise an immune response, allows specific antibodies to be collected. Mixing these with similar proteins from other species allows agglutination. The more agglutination, the more closely related the species are
What is Biodiversity
The variety of living organisms in a particular habitat
What is a habitat?
Where an organism lives
What is population
organisms of one species that occupy the same habitat at the same time and are able to interbreed
What is a community
All of the organisms from each population in a habitat
How can you measure biodiversity?
- species richness - number of different species in a community
- index of diversity
impact of farming on biodiversity
- removal of hedges, removes habitat for other species
- large areas of monoculture reduces variety of foods for other species
- pesticides may kill non-pests species
- fertilisers may leach into water ways causing eutrophication
- fertilisers may make soil too nutrient-rich for wild plants to grow
- harvesting crops/ ploughing/ grazing prevents taller species growing
what do larger values fro standard deviation show?
data is less reliable
what do smaller values fro standard deviation show?
data is more uniform and more reliable data
what is standard deviation
spread of data around the mean
overlap on standard deviation
there is no significant difference
spearman’s rank correlation coefficient
- measurement- the investigation involved taking measurements.
- looking for associations between different measurements made from the same sample
student’s t-test
- measurement- the investigation involved taking measurements.
- looking for differences between same measurements from different samples
chi-squared test
frequencies- the investigation involved finding the number of individuals in particular categories
correlations coefficient
if the result is greater than the critical value…
- our result is greater than the critical value …
- This means there is a significant correlation
- There is a less than …% probability that the correlation is due to chance
- We reject the Null hypothesis
correlations coefficient
if the result is less than the critical value…
- Our result is less than critical value …
- This means there isn’t a significant correlation.
- There is a greater than …% probability that the correlation is due to chance
- We accept the Null hypothesis
correlations coefficient
p > 0.01
- the probability of getting this correlation by chance is greater than 1%.
- there is no significant correlation at the 1%
what is directional selection
selection favours individuals that vary in one direction from the mean of the population
what is stabilising selection
selection favours average individuals
polygenes
characteristics influenced by multiple genes
all members of the same species have the same …
genes
what happens when alleles are different
each allele has a different base sequence producing a different polypeptide
