GENETIC INFORMATION, VARIATION & RELATIONSHIPS BETWEEN ORGANISMS Flashcards
What are the differences between DNA in eukaryotes and prokaryotes?
Eukaryotic DNA:
- long & linear, wound up
- wound around proteins called histones (help support DNA)
- held in nucleus
- mitochondria & chloroplasts have their own DNA, circular & short, not associated with histones (similar to prokaryotic DNA)
Prokaryotic DNA:
- short & circular
- isn’t wound around histones, condenses to fit by supercoiling
- held in cytoplasm
What is a gene?
Base sequence of DNA that codes for polypeptide or functional RNA.
- Order of bases in a gene determine order of amino acids in polypeptide
- Each amino acid coded by sequence of three bases in a gene = triplet
What is a genome?
Complete set of genes in the cell
What is a proteome?
Full range of proteins that the cell is able to produce
What is the genetic code?
Sequence of bases in length of DNA code for sequence of amino acids in polypeptide or functional RNA
What are characteristics of the genetic code?
Degenerate- more than one codon can code for the same amino acid
Universal- same specific base triplets code for the same amino acids in all living things
What are exons?
Areas that code for amino acids within the genes
What are introns?
Areas that are non-coding, do not code for a polypeptide
What is a mutation?
- Any change to the quantity or base sequence of the DNA of an organism
- If mutation occurs during formation of gametes, it may be inherited and cause a dramatic change to a species
What is a gene mutation?
Any change to 1 or more nucleotide bases or a change in the sequence of bases of the DNA
What is a base substitution and what is its effect?
- If a base is replaced with another nucleotide that has a different base
- Effect depends on base that’s changed. If it changed the amino acid, the polypeptide will be a different shape so no longer have its function.
- Sometimes there’s no change in amino acid due to degenerate nature of genetic code
What is a base deletion / addition and what is its effect?
- A gene mutation caused when a nucleotide is lost from or added to the normal DNA sequence
- Causes a frame shift, all the triplets from that point on will be affected
What is a chromosome mutation and what are the 2 types?
Changes in the structure or number of whole chromosomes
- Changes in whole sets of chromosomes
- condition called polyploidy, organism has 3 or more sets of chromosomes rather than the normal 2 - Changes in number of individual chromosomes
- where homologous pairs of chromosomes do not separate during meiosis (non-disjunction), so one gamete gets 1 extra chromosome and one gets 1 less
What is variation?
- Means ‘differences’ between individuals in a species
- Helps a species adapt to a changing environment for survival
How do you get variation?
- Sexual reproduction
- Mutations
What is meiosis and what does it produce?
Cell division to form a gamete (sex cell)
- forms 4 daughter cells that are haploid (half the number of chromosomes of the parent cell), only containing 1 set of chromosomes so when fertilisation occurs the normal amount of chromosomes is restored
What is the process of meiosis?
FIRST DIVISION
Interphase:
- Chromosomes are not visible
- Chromosomes start to replicate & become visible
Prophase 1:
- Chromosomes condense
- Nuclear envelope breaks down
- Crossing over occurs between homologous chromosomes
Metaphase 1:
- Pairs of homologous chromosomes move to equator of cell, attached via centromeres on spindle fibres
- Arrange themselves randomly (independent assortment)
Anaphase 1:
- Homologous chromosomes move to opposite poles of cell as spindle fibres contract
Telophase 1:
- Nuclear membrane starts to reform
- Chromosomes gather at poles of cells
Cytokinesis 1:
- Cytoplasm divides, 2 daughter cells are formed
SECOND DIVISION
Prophase 2:
- Nuclear membrane disappears
- Centreioles produce new spindle fibres which form around chromosomes and attach to centromeres
Metaphase 2:
- Chromosomes randomly line up at equator
Anaphase 2:
- Centromeres divide
- Spindle fibres contract, pulling sister chromatids to opposite poles of cell
Telophase 2:
- Nuclear envelop reforms around chromatids
- Cytoplasm begins to divide
Cytokinesis 2:
- Cytoplasm divides
- 4 genetically different haploid daughter cells are produced
What is non-disjunction and what are its effects?
‘Failure to separate’
- Where homologous chromosomes or sister chromatids don’t separate properly during meiosis
- The effects vary depending on chromosomes affected, but often very serious
How does non-disjunction lead to downs syndrome?
- Non-disjunction of chromosome 21 (2 copies of chromosome 21)
- During fertilisation, if 1 gamete within 2 copies of chromosome 21 fuses with a gamete with a normal number of chromosomes, the result is a cell with 3 copies of chromosome 21, resulting in downs syndrome
What is karyotyping?
Process of pairing and ordering all chromosomes of an organism, providing a genome - wide snapshot of an individuals chromosomes
What is genetic diversity?
- The number of different alleles in a given species
- High genetic variation = high number of different alleles
What is the process of transcription?
- Occurs in the nucleus, converting DNA into mRNA
1. Helicase enzyme unzips DNA strands, hydrogen bonds break, exposes chain
2. RNA polymerase joins free RNA nucleotides to their complementary DNA bases until STOP codon
3. Phosphodiester bonds are formed between RNA nucleotides
4. Pre-mRNA strand is produced
5. In eukaryotic cells, splicing occurs to remove introns, producing mRNA
6. mRNA leaves nucleus through nuclear pores and joins to ribosomes in cytoplasm
What is the process of translation?
- Occurs in ribosomes within the cytoplasm, converting mRNA to polypeptide chain / protein
1. tRNA travels to ribosome carrying specific amino acid to mRNA strand
2. tRNA molecules have an anticodon (triplet code) that is complementary to the amino acid
3. tRNA molecules carry each amino acid to the mRNA one at a time by complementary base pairing
4. Peptide bonds form between amino acids - requires ATP
5. Once reached a STOP codon - termination
6. Produces the final polypeptide
How is genetic diversity increased?
- Meiosis
- Genetic mutations, creating new alleles
The greater the genetic diversity, the more likely the species will adapt to environmental change due to a wider range of alleles so a wider range of characteristics (higher probability of an individual possessing those traits to survive)
What is natural selection?
- Only certain individuals are reproductively successful & pass on alleles to offspring (affects allele frequency in a population)
- Mutation of gene results in new alleles joining gene pool
- Mutation may give possessor of gene an advantage as they’re better adapted so more likely to survive
- Over generations, new genes increase and old genes decrease (also changes allele frequency)
What is selection?
Process by which organisms are better suited to environments and tend to survive and breed, those less suited tend not to survive and breed
What is directional selection?
Single phenotype is favoured, causing allele frequency to continuously shift in one direction, changes the characteristics of the population
- Population’s trait distribution shifts towards the other extreme
- The mean of the population graph shifts
- Eg: length of giraffes neck, longer = reach trees to eat
What is stabilising selection?
When selective pressures select against the two extreme of a trait
- May favour average individuals, will maintain characteristics of the population
- Eg: Plant height, too short = no sunlight, too tall = exposed to wind damage (combined, these 2 selective pressures maintain plants of medium height, number of medium plants increase, number of short and tall plants decrease)
What is a species?
Members of the same species can breed with each other to produce living, fertile offspring
What is classification?
Organisation of living things into groups according to their similarities
What is the binomial system by Linnaeus?
- Uses Latin or Greek names, written in italics
- First name = Generic name, the Genus to which the organism belongs to (has capital letter)
- Second name = specific name, this is the species (has lowercase letter)
What is the order of the classification system?
Domain Kingdom Phylum Class Order Family Genus Species
What is artificial classification?
- Divides organisms by physical characteristics
- Non-genetic or non-evolutionary
What is phylogenetic (natural) classification?
- Based upon evolutionary relationships
- Classifies species using shared features derived from their ancestors
- Arranges the groups into a hierarchy (groups contained within larger groups with no overlaps)
What is phylogeny?
Study of evolutionary relationships between organisms
What are the 3 different domains?
Domain Archea:
- Prokaryotes
- Includes newly discovered cell types
- Contains 1 kingdom = the Archaebacteria
Domain Bacteria
- Prokaryotes
- Includes other members of old kingdom Monera
- Has 1 kingdom = the Eubacteria
Domain Eukarya
- Eukaryotes
- Includes all kingdoms composed of organisms made up of eukaryotic cells = protista, fungi, animalia, plantae
What is anatomical evidence?
- Structure similarities called homologies, show structures present in a common ancestor
- Organisms with homologous structures are thought to be closely related
- The higher the number of homologous structures between 2 species, the closer they are in the phylogenetic tree
What is embryological evidence?
- The more similar embryos look, the close they are phylogenetically
- Evidence that organisms evolved from a common ancestor
What is biochemical evidence?
- Used to determine how closely related organisms are
- Refines idea of classification and leads to reclassification of some species
1. Amino acid sequence comparison
2. DNA sequence comparison
3. mRNA sequence comparison
What is courtship behaviour?
Helps ensure mating is successful and offspring has the greatest chance of survival by:
- recognising members of their own species
- identifying a male/opposite sex that is capable of breeding
- forming a pair bond
- synchronise breeding
- become able to breed
These behaviours are genetically determined
What is biodiversity and what are its 3 components?
Describes variety in the living world. Refers to the number and variety of living organisms in a particular area. Has 3 components:
- Species diversity- number of different species & number of individuals of each species within a community
- Genetic diversity- variety of genes possessed by individuals that make up any one species
- Ecosystem diversity- range of different habitats within a particular area
How to measure species diversity?
Index of diversity:
N (N-1) d= species diversity index
d = _______ N= total no. of organisms of all species
{ n (n-1) n= total no. of organisms of each species
{= sum of
What is species richness?
Measure of the number of different species in a community
What does quantitative investigations of variation within a species involve?
- 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 the impact of agriculture on species diversity?
- Farmers select crops that are more productive
- The frequency of alleles is reduced
- For economic reasons, crop yield needs to be large
- Any one area can only support a certain amount of
biomass (if most of this area is taken up by a crop,
then there is little area left for anything else eg habitats)
What is the impact of deforestation on species diversity?
- Forests contain many varied and different habitats =
high species diversity, permanent clearing of the forest leads to loss of habitats & loss of biodiversity - Removal of hedgerows and grubbing out of woodland
- Creating monocultures, eg replacing natural meadows with grass for silage
- Filling in ponds and draining marshland and bogs
- Overgrazing of land, eg upland areas by
sheep that prevents the re-growth of woodland.
What are farming practices which reduce species diversity?
- Crops are sprayed with pesticide and man made fertiliser, harming species
- Escape of effluent from silage and slurry tanks into
water courses - Absence of crop rotations or a lack of intercropping or undersowing
What are farming practices which improve species diversity?
- Introduce conservation headlands (strip of land
around a field where natural plants are encouraged
and pesticides/herbicides are not used) - Leave the cutting of unimproved grassland until after
flowering and seeds have been disbursed.
