science

Evolution

Gradual changes occurring in a population over a long time as organisms become better adapted to a specific environment

Microevolution

Changes in allele frequency within a population

Macroevolution

Large changes in shape/structure leading to speciation

Gene pool

• The ratio of all genes/alleles in a population
• Changed by microevolution

Evolution through natural selection (ICEAGE)

• I - Inherited genetic variation from mutation • C - Competition from overproduction and struggle to survive • E - Environmental selection (external factors) • A - Adaptations • G - Genotypic frequency (allele giving selective advantage increases in next gen) • E - Evolution

Species (definition)

Members of the same species must be able to produce fertile offspring

Predation (definition)

A feeding relationship where a predator obtains food by killing and eating prey

Adaptations (definition)

• Inherited structural, behavioural, or physiological characteristics allowing an organism to survive and reproduce
• Occurs across populations, not within a lifetime

Examples of adaptations

• Behavioural - migration, courtship, food choices
• Physical - colour change, venom

Types of adaptations

• Structural - features of the organism's body
• Behavioural - ways they behave to increase survival/reproduction
• Physiological - internal chemical processes of the organism's body

Requirements of plants

• Light
• Water
• Nutrients
• Competition for these drives adaptations

Requirements of animals

• Water
• Nutrients
• Shelter
• Mates

Biotic features

• Predation
• Competition
• Disease

Abiotic features

• Temperature
• pH
• Moisture
• Light intensity

Prey adaptations

• S - Armour making consumption difficult
• B - Nocturnal behaviour to avoid predators
• P - Autotomy (detaching body parts to escape)

Predator adaptations

• S - Claws/teeth to attack and retract for walking
• B - Stalking to close distance without detection
• P - Metabolic system expands to produce venom

What to include in an adaptation question

• Type (Physiological, Structural, or Behavioural)
• Outline the adaptation
• Link to survival/reproduction

Effect of mutations on resulting protein

• Reduced function
• Subsequent codons affected if frameshift causing multiple missense mutations

Same genotype doesn't always equal same phenotype

Due to the interaction of genes and the environment

Types of nuclear division

• Mitosis
• Meiosis

Mutagens (definition)

Chemical or physical agents that cause a change in the DNA sequence

Types of mutagens

• Ionising radiation
• Chemicals
• Infectious agents

Ionising radiation (as mutagen)

• Knocks off electrons
• Ionises biochemical compounds in cells forming free radicals
• Causes damage to DNA and proteins

Chemicals (as mutagen)

• Insert into DNA instead of bases and between them
• Cause problems during DNA replication
• E.g. cigarette smoke

Infectious agents (as mutagen)

E.g. HPV, Helicobacter pylori

Causes of mutations

• Mutagens
• Spontaneous errors in DNA replication or meiosis

Genetic code determines

• Sequence of bases in DNA
• Which amino acids are used and in what order
• Folding and function of the polypeptide

RNA function

Transfer information and translate it into proteins

DNA function

Store long-term genetic information as a blueprint

RNA vs DNA

• Single stranded
• Ribose sugar
• Bases A, U, G, C
• Found in nucleus and cytoplasm
• Short lifespan

DNA vs RNA

• Double stranded
• Deoxyribose sugar
• Bases A, T, G, C
• Remains in nucleus and mitochondria
• Long lifetime

Similarities between RNA and DNA

• Both are types of genetic material and nucleic acids
• Same basic makeup
• Four types of nitrogenous bases with double and triple bonds

Cell division is semi-conservative

Daughter cells have one parent strand and one newly synthesised strand

BRCA 1 and 2

• Genes that repair damaged DNA
• Prevent mutations causing breast/ovarian cancer
• Inherited but can be lost or damaged

Ethical framework principles

• Autonomy (choice)
• Non-maleficence
• Beneficence
• Justice (equal distribution)
• Confidentiality
• Non-deception

Gene cloning process

• Satellite DNA (plasmid) replicates independently
• Foreign gene inserted into bacterial plasmid to make recombinant DNA
• Bacteria reproduces and replicates the foreign gene

Meiosis (vs mitosis)

• Forms gametes
• Sexual reproduction
• n chromosomes in daughter cells
• 4 daughter cells
• 2 cell divisions
• Generates genetic variation

Mitosis (vs meiosis)

• Growth and repair of cells
• Asexual
• 2n chromosomes in daughter cells
• 2 daughter cells
• 1 cell division
• No genetic variation

Golden ratio of phenotypes

3:1

Generations in order

• P generation
• F1 generation
• F2 generation

Mechanism of spore formation

• Genetic material released and tough coats form around DNA
• Spore dries out and becomes dormant
• Activated by germination in good conditions

Organisms that use fragmentation/regeneration

Moss, flatworms, fungi, coral

Types of asexual reproduction

• Spore formation
• Vegetative reproduction
• Budding
• Fragmentation/regeneration
• Binary fission

Asexual reproduction advantages

• Rapid growth (fast reproduction rate)
• One parent needed (less time/energy)
• Produces clones that fit a stable environment

Asexual reproduction disadvantages

• No variation so entire population can be impacted by disease/condition change
• Rapid growth leads to competition for resources

Asexual reproduction

• One parent
• No sperm/eggs
• Offspring produced by mitosis
• Chromosome number remains the same

Sexual reproduction

• Two parents
• Suited to changing environments
• Involves fusion of gametes via meiosis

In common between chromosomal and gene mutations

• Both can be heritable (germline) or non-heritable (somatic)
• Can be harmful, beneficial, or neutral
• Can occur spontaneously or be induced by mutagens

When does point/gene mutation occur

During DNA replication in S phase of interphase

Effect of early termination

Protein is non-functional and the rest of the sequence is not coded for

Translation

• Two codons read through two ribosomal units
• tRNA anticodon attaches with amino acid
• Amino acids bonded by peptide bonds
• Codon becomes naked and shifts
• Continues until termination triggers release of polypeptide chain and ribosome disassembles

rRNA function

• Holds mRNA in place for binding to tRNA so amino acids can be joined
• Acts as a conveyer to assist polypeptide chain elongation

tRNA function

• Clover-shaped short segment of RNA
• Shuttles amino acids to the ribosome to be joined

mRNA function

• Single strand complementary to DNA template strand
• Carries genetic instructions from DNA (nucleus) to ribosome (cytoplasm)
• Exposed to and read by ribosome

Importance of proteins

• Structural components
• Enzymes that catalyse chemical reactions
• Hormones as chemical messengers
• Antibodies that fight infection
• Transport (e.g. haemoglobin carries oxygen in blood)

Why meiosis is important

Two sets of n chromosomes from each parent are fertilised to restore the diploid number

Mutation (definition)

A permanent change in the sequence of bases resulting in new alleles

Chromosome (definition)

Long strings of DNA wrapped around proteins to make them compact

Eukaryotic DNA vs Prokaryotic DNA

• Eukaryotic - linear, associated with histone proteins
• Prokaryotic - single circular loop, no histones

Scientists who discovered DNA structure

Franklin, Watson, Crick, Wilkins

Purines vs Pyrimidines

• Purines - A and G, double ringed structure
• Pyrimidines - C, U and T, single ringed structure
• Bind together to keep strands equidistant
• C and G have triple hydrogen bonds and are stronger

Gene (definition)

A section of DNA that codes for a polypeptide/protein

DNA components

• Deoxyribose pentose sugar
• Phosphate molecule
• Nitrogenous base

Transgenesis (definition)

Procedure of transferring genetic material from one species to another

Biotechnology (definition)

Use of biological materials as tools to fulfil human needs/demands

Height and nutrition

• Genetics dictate the height available
• Nutrition fulfils that potential
• Nutrition acts as signals turning genes off or on but does not alter DNA

Cell development

• 1. Sperm enters ovum
• 2. Fertilisation - becomes zygote
• 3. Mitosis
• 4. Differentiation - cells specialise due to different conditions

Polymer (definition)

A large molecule made of similar smaller molecules in a chain

Polypeptide (definition)

A chain of amino acids joined by peptide bonds

Karyotypes

• 22 pairs of autosomes
• 1 pair of sex chromosomes
• Homologous pairs share the same loci order, same size, one from each parent

Restriction enzyme process

• Cut double-stranded DNA
• Create exposed overhangs/sticky ends
• Find complementary sticky ends
• Reform hydrogen bonds
• Ligase reconnects backbones by re-establishing phosphodiester bonds

Restriction enzymes

• Defence system in bacteria against viruses
• Used in humans to isolate a gene of interest
• Target particular sequences of bases in DNA

Transgenesis

• Creates organism with new desirable genetic makeup
• Inserts a protein/trait not normally expressed
• Works because DNA is universal
• Creates new transgenic species (until they divide)

Flower colour and pH

• Anthocyanins are sensitive to pH
• Low pH (acidic) = pink
• High pH (alkaline) = blue (absorbs more aluminium)
• The chemical structure of the pigment changes

DNA (definition)

• A polymer made of two strands forming a double helix
• Arranged as chromosomes/chromatin in the nucleus of eukaryotic cells

Watson and Crick's discovery about DNA

• Used X-ray crystallography of DNA (Photo 51) from Franklin and Wilkins
• Determined double helix structure
• Two phosphate-sugar backbones antiparallel
• Backbones joined by nitrogenous bases held by hydrogen bonds

Protein (definition)

A single polypeptide chain folded to a specific 3D shape

Melanin and skin colour process

• UV reaches skin
• DNA in skin cells is damaged
• Melanocytes produce more melanin
• Melanin acts as a protective layer to absorb more UV radiation

Once bacteria has reproduced

It is no longer part of the transgenic specie

Mutations in all organisms

All organisms have a low spontaneous mutation rate induced by the mutagenesis process