5th Part Bio Exam PDF

ENZYMES METABOLISM The totality of chemical reactions that occur within a cell or organism Controlled and coordinated by enzymes Metabolic reactions serve two key functions within organisms - They provide a source of energy for living processes (such as movement and...

ENZYMES METABOLISM The totality of chemical reactions that occur within a cell or organism Controlled and coordinated by enzymes Metabolic reactions serve two key functions within organisms - They provide a source of energy for living processes (such as movement and reproduction) - They enable the synthesis and assimilation of new organic materials for use within the cell Nutrients are converted into new materials and energy (waste excreted) TYPES OF METABOLISM Metabolic reactions can be classed as either anabolic or catabolic Anabolism – building complex macromolecules from simpler biomolecules – requires energy - Examples: photosynthesis and formation of organic polymers Catabolism – breaking down the macromolecules into simpler building blocks – releases energy - Examples: digestion (via hydrolysis) and respiration (via oxidation) ENZYMES Enzymes are globular proteins that act asC biological catalysts by increasing the rate of reaction Enzymes are not consumed by the reactions they catalyze and can be continually re-used An enzyme will catalyze the chemical conversion of reactants (substrates) into products - Enzymes are named according to their substrate and end with the suffix ‘-ase’ (e.g. lipase) SUBSTRATE SPECIFICITY The region on the surface of the enzyme to which a substrate binds is called the active site An active site is complementary in shape and charge to a substrate The active site is only composed of a few amino acids but makes a unique 3D shape Different enzymes are required to catalyze the conversion of different substrates surate & made of amino-acso ACTIVATION ENERGY Enzymes catalyze chemical reactions by lowering the activation energy the reaction needs The activation energy threshold (EA) is the level of energy required to trigger the reaction  CATALYSIS The enzyme’s active site is not a completely rigid structure and will change shape to fit the substrate (conformational change) - induced fit model ? This change in structure promotes catalytic activity in the enzyme: - The conformational changes stress bonds in the substrate and increase the reactivity of the molecule (lower activation energy) - The conformational change in shape allows for broad specificity (for example, a lipase can bind to a variety of different lipids) -G ENZYME ACTIVITY Enzyme activity can be measured via the consumption of substrates or formation of C products The rate of reaction can be determined by the time taken to achieve a particular outcome Examples of methodologies for measuring the activity of enzymatic reactions may include: FACTORS AFFECTING ACTIVITY Rate of an enzyme-catalyzed reaction can be affected by: - Changing the frequency - of successful collisions between the enzyme and the substrate * - Changing the capacity for the substrate to interact with the enzyme (e.g. via - denaturation) Factors that affect the activity of an enzyme-catalyzed reaction: Temperature, pH, Substrate concentration, Enzyme concentration MOLECULAR COLLISIONS Enzymes and substrates have to collide in the correct orientation to interact - a substrate must bind to the active site The rate of enzyme activity can be improved by increasing the frequency of successful collisions by: - Increasing the level of molecular motion ( kinetic energy) - Increasing concentrations of particles (enzyme or substrate) Enzymes or substrates may be immobilized (e.g., embedded in a membrane) to localize the chemical reaction to a certain style DENATURATION Enzyme activity is dependent on the 3D shape of a protein (tertiary structure) - Catalysis will only occur if the substrate can successfully bind to the enzyme’s active site Denaturation can diminish enzyme activity by- breaking the bonds involved in protein folding - This may cause the deformation of the active site, preventing the substrate from binding - TEMPERATURE Low temperatures - limited motion/activation energy) Increasing the temperature increases the kinetic energy of the enzyme and substrate (more frequent collisions) At an optimum temperature the reaction rate will peak (optimal temperature will be dependent on the enzyme) - High temperatures - decrease in activity due to denaturation · "temperature Kinetic energy of enzyme /substrate peak A PH Changing the pH will alter the charge of the enzyme, changing both the solubility and shape of the protein - less successful collisions Enzymes will have an optimal pH at which the activity is highest Enzyme activity will decrease as the pH moves outside of this optimal range (the enzyme becomes denatured) enzyme activity SUBSTRATE CONCENTRATION Increasing substrate concentration will increase the rate of enzyme activity, but only up to a certain point More substrate - greater chance of a successful collision S At a certain point, the reaction rate will start to plateau - solution becomes saturated with the substrate and all active sites are occupied PHOTOSYNTHESIS Photosynthesis is a process in which some organisms use the light energy from the Sun to synthesise organic compounds The chemical energy stored in these carbon compounds can then be released E by cellular C respiration to produce usable energy (ATP) Photosynthesis equation: LIGHT SPECTRUM Photosynthesis uses wavelengths from the visible portion of the electromagnetic spectrum The spectrum of visible wavelengths range from 400nm to 700nm and appear as colours From longest to shortest wavelength: red – orange – yellow – green – blue – indigo – violet PHOTOSYNTHETIC PIGMENTS Photosynthetic pigments are used to absorb light energy The main photosynthetic pigment found in nature is chlorophyll Chlorophyll absorbs red and blue light, while green light is reflected ABSORPTION VS. ACTION SPECTRA Cby photosynthetic pigments Absorption spectra show wavelengths absorbed C Action spectra shows the wavelengths used by pigments in photosynthesis separation CHROMATOGRAPHY ~ & Chromatography is a technique used to separate pigments by size - Pigments are dissolved within an organic solvent (‘fluid’ phase) - Fluid is then passed through a static material (‘stationary’ phase) - Pigments will move at different speeds and separate - A retardation factor can be calculated to identify each pigment chemical energy light < PHOTOSYNTHETIC STAGES Photosynthesis involves two sets of reactions: - - The light-dependent reactions convert light energy into usable chemical energy (ATP) - The light-independent reactions use this chemical energy to synthesize organic compounds ↳ chemical synthesize organic compounds energy > - LIGHT-DEPENDENT REACTIONS The light-dependent reactions convert light energy into ATP - Light is absorbed by photosynthetic pigments, resulting in the excitation of their electrons The energized electrons are then used to synthesize chemical energy (ADP + Pi → ATP) Light is also absorbed by water, which is split (photolysis) to produce hydrogen and oxygen ATR D for anabolic process CARBON DIOXIDE ENRICHMENT Carbon atoms (from carbon dioxide) are combined to form organic compounds Hydrogen atoms (obtained from splitting water) are also incorporated into the compounds ATP (produced by chlorophyll) provides the energy needed to power this anabolic process The light-independent stage uses hydrogen + ATP from the previous stage to fix the carbon Modern industrial processes utilize the combustion of organic materials (i.e. fossil fuels) as a means of producing energy – with carbon dioxide produced as a by-product of this reaction - An artificial version of cell respiration The increase in atmospheric carbon dioxide concentrations has altered global temperatures and climate patterns, but will also influence the growth of plants and rates of photosynthesis CO2 enrichment experiments can be used to predict the outcomes of changes to CO2 levels Enclosed greenhouse experiments allow for- greater control of variables Free air CO2 enrichment (FACE) represents open systems that involve natural conditions Examples: enclosed greenhouse experiments and free air carbon dioxide enrichment LIMITING FACTORS As photosynthesis involves multiple stages and several essential conditions, a variety of factors may limit reaction rates (a condition nearest its minimum value is the limiting factor) Factors that may influence the rate of photosynthesis in organisms include: - Light intensity – Higher intensities increase chlorophyll photoactivation (until saturation) - Wavelengths of light – Red and blue light are better absorbed by photosynthetic pigments - Carbon dioxide levels – CO2 is used to synthesize glucose (it is a photosynthetic substrate) - Temperature and pH – These conditions will affect the activity of photosynthetic enzymes PHOTOSYNTHESIS EXPERIMENTS Photosynthesis is identified by measuring the uptake of inputs or the production of outputs Carbon Dioxide Uptake: C - CO2 levels in solutions can be measured via a change in pH (forms carbonic acid in water) - - Can be measured indirectly as a change in biomass (by measuring the dry weight of a plant) Oxygen Production: - - Changes in O2 levels can be detected as a change in gas volume (measured with a syringe) - E Oxygen levels can also be measured based on the production of air bubbles from stomata Note: Control groups are required to establish the basal levels of cell respiration in plants CELL RESPIRATION covalent bond > - ATP (ADENOSINE TRIPHOSPHATE) & Energy is a property that exists in different forms and represents the capacity to do work Organic molecules store chemical energy in their covalent bonds (as high-energy electrons) This energy is not readily accessible to the cell but can be- transferred to a coenzyme for use Immediately available energy source within the cells Nucleotide–base adenine, the five-carbon sugar ribose, and three phosphate groups & Soluble in water Stable at pH levels close to neutral Cannot pass freely through the phospholipid bilayer The third phosphate group of ATP can easily be removed and reattached by hydrolysis and condensation reactions Hydrolysing ATP to ADP and phosphate releases a relatively small amount of energy ATP – COENZYME -C Coenzymes are organic compounds that shuttle components needed for enzymatic reactions Coenzymes cycle between a loaded form and an unloaded form ATP transfers energy in a usable form for cells Sometimes the phosphate group is linked to another molecule (protein pump or a substrate in a metabolic reaction) - when it detaches energy is released – causing a change in the molecule  E.g. a conformational change in a membrane pump or a chemical change that converts a substrate into a product ADP to ATP conversion requires energy: - Cell respiration, photosynthesis, chemosynthesis PROCESSES THAT REQUIRE ENERGY Biosynthesis of macromolecules Anabolic reactions use ATP to synthesize complex macromolecules Active transport ATP is required to move materials against a concentration gradient causes reversible changes in the conformation of the pump protein - more to less stable one conformation = the particle can enter it from one side of the membrane other conformation = the particle can exit on the other side of the membrane - Usually uses oxygen and releases carbon dioxide Movement of O and CO in and out of the cell–gas exchange by simple diffusion 2 2 - Interdependent Movement inside and of the cell - Chromosomes, vesicles controlled release of energy TO compounds - Cytokinesis, muscle contractions from organic - produce ATP 2 CELL RESPIRATION Cell respiration is the controlled release of energy from organic compounds to produce ATP - The energy is released when organic compounds are broken down (oxidized) by enzymes The main organic compounds used are carbohydrates (glucose and fatty acids) - Lipids can be broken down to release more energy, but are harder to transport and digest - Proteins can also be digested, but produce toxic nitrogenous wastes that must be excreted TYPES OF RESPIRATION Cell respiration can occur via one of two distinct mechanisms: - Anaerobic: The partial breakdown of organic compounds (glucose) for a small yield - - of ATP - Aerobic: The complete breakdown of organic compounds for a much larger yield of - w ATP Note: Lactic acid is only produced by animals, plants and fungi produce ethanol and CO2 RESPIRATION COMPARISON em used only anceroic les in CELL RESPIRATION IN HUMANS lungs and blood system supply oxygen to most organs of the body rapidly enough for aerobic respiration mu & anaerobic cell respiration is sometimes used in muscles - it can supply ATP very rapidly when we need to maximize the power of muscle contractions Lactate (lactic acid) is a waste product of anaerobic respiration in muscles - there is a limit to the concentration that the human body can tolerate and this restricts how much anaerobic respiration can be done The lactate must be broken down - requires oxygen – the oxygen debt. LIMITING FACTORS The law of limiting factors states that when a chemical process depends on more than one essential condition, the rate of reaction is limited by the factor nearest to its minimum value Cell respiration is dependent on several different conditions: - temperature, pH, glucose concentration, oxygen levels TRANSCRIPTION AND TRANSLATION > flow of genetic information CENTRAL DOGMA - - The central dogma of molecular biology describes the flow of genetic information within a cell DNA may be copied during the formation of new cells via the process of DNA replication - RNA transcripts may be synthesized from a DNA template via the process of transcription - Proteins are assembled from the code contained within the RNA transcripts via translation - TRANSCRIPTION Transcription is synthesis of an RNA sequence from a DNA template (only one DNA strand is transcribed) C A sequence of DNA that is transcribed into RNA is called a gene GENE !!! RNA POLYMERASE Binds to a site on the DNA at the start of the gene that is being transcribed Unwinds the DNA separating it into two single strands (template and coding strands) Moves along the template strand positioning RNA nucleotides with complementary bases links the RNA nucleotides by covalent sugar-phosphate bonds to form a continuous strand of RNA Detaches the assembled RNA from the template strand and allows the DNA double helix to reform. Transcription stops when a sequence that indicates the end of the gene is reached Each nucleotide added to the RNA strand must have a base that is complementary to the base on the template DNA strand Pairs of bases are complementary because they form hydrogen bonds with each other but not with other bases The DNA strand with the base sequence to be copied into RNA is called the sense strand (or the coding strand). The other strand is called the template strand (or the antisense strand) à Transcription of this strand results in a strand of RNA with the same base sequence as the sense strand of DNA except that uracil is replaced by COMPLEMENTARY BASE PAIRING  the bases are only briefly vulnerable to chemical changes that would cause mutation – when they are separated The stability of DNA templates is essential because they may be transcribed many times during the life of a cell If mutations were common frequently used templates would accumulate mutations and the RNA copies would contain more and more errors Proteins translated from these copies would have increasing numbers of amino acid substitutions GENE EXPRESSION Not all genes in a cell are expressed at any given time (transcriptional activity is regulated) Genes can be switched ‘on’ or ‘off’ by controlling the rate of transcription within the cell - Transcription factors regulate expression by controlling the activity of RNA polymerase of production polypeptides ↑ TRANSLATION & - Translation is the process of protein synthesis and describes the production of polypeptides In the cytoplasm in ribosomes The polypeptides are translated from an mRNA sequence - generated by transcription TYPES OF RNA There are three main types of RNA produced via transcription and involved in translation: Messenger RNA (mRNA) is a transcript of the DNA instructions (codes for a polypeptide) 5+ o Transfer RNA (tRNA) carries the protein subunits (amino acids) to the mRNA transcript mRNA Ribosomal RNA (rRNA) provides the - catalytic activity for combining the amino acids ↓ proteins proteina rRNA & RIBOSOMES - he ribosome consists of two subunits made of protein and rRNA The two subunits interact with RNA in order to assemble amino acids & The small subunit binds to mRNA (codes the genetic instructions) - The large subunit binds two tRNA molecules (carries amino acids) and has a catalytic site that makes& 1 peptide bonds between amino acids codons- a sequence of 3 bases mRNA AND tRNA The messenger RNA is progressively ‘read’ by a ribosome in triplets of bases called codons Each codon is recognised by a complementary anticodon on a specific tRNA molecule * The large ribosomal subunit binds to two tRNA molecules simultaneously and transfer amino acids from one tRNA molecule to the next Amino acids are linked by peptide bonds As a ribosome moves along mRNA, tRNA molecules are replaced by new molecules ⑳ PRODUCTION OF POLYPEPTIDES The ribosome moves along the mRNA molecule, reading the sequence in base triplets (or codons) Specific tRNA molecules will align opposite a given codon via a complementary anticodon Each tRNA molecule carries an amino acid The ribosome moves along the mRNA and links o amino acids by peptide bonds (via condensation) This process synthesizes a polypeptide chain  translated mRNA sequence are - THE GENETIC CODE The genetic code is the set of rules that determines how mRNA sequences are translated A sequence of three bases on the mRNA is called a codon 3 It designates the specific amino acid encoded for by every codon (4 = 64 combinations) Universality – All living organisms use the same code (there are a few viral exceptions) Degeneracy – More than one codon may code for the same amino acid (only 20 in total) o Translation is initiated at a start codon (AUG) and will proceed until a stop codon is reached The start codon establishes the correct reading frame for translation Sin Translation ~ of an mRNA sequence will: - Begin with a start codon (AUG = Met) - End with a stop codon (UGA, UAA, UAG) DNA REPLICATION DNA replication is required for cell reproduction DNA is duplicated during theE S phase of interphase →chromosomes comprised of two identical sister chromatids SEMI-CONSERVATIVE Semi-conservative – one strand from the template, one strand newly synthesized ENZYMES IN DNA REPLICATION C & ARTIFICIAL METHODS DNA TECHNOLOGIES Polymerase Chain Reaction E - PCR is an artificial method for amplifying DNA (makes large quantities of a set sequence) - & - It uses variations in temperature (via a thermal cycler) to control the replication -process Gel Electrophoresis & - Gel electrophoresis is an artificial method for separating DNA molecules according to - size - - - It uses electrical currents (‘electro’) to move the DNA (’phoresis’) through a matrix (‘gel’) POLYMERASE CHAIN REACTION - PCR is an artificial method of DNA replication used to rapidly amplify a target sequence > Three key steps are repeated in a cycle: - Denaturation – Heat is used to separate the DNA strands - Annealing – Primers added to designate copying region - Elongation – Taq polymerase synthesizes new strands - 30 cycles will generate >1 billion copies of the DNA  of separation DNA ↑ - GEL ELECTROPHORESIS Gel electrophoresis is an artificial method that separates DNA fragments according to molecular size (measured in kilobases) [ The fragments are placed into an agarose gel that is subjected to an electrical charge→ fragments move to the positive anode process Larger DNA fragments will encounter more resistance from the gel matrix and will move slower than smaller DNA fragments larger fragments appear nearer to the top of the gel Size can be determined using known fragments for reference DNA APPLICATIONS Three potential applications of these DNA technologies include: - Profiling – Determining the relatedness between individuals based on DNA comparisons - Gene Cloning – Introducing new DNA into organisms via a molecular vector (i.e. plasmid) - Sequencing – Identifying specific base sequences of DNA using a the Sanger method DNA PROFILING Non-coding DNA sequences may contain recurring elements known as short tandem repeats (STRs) The number of repeats differs between individuals Gel - & electrophoresis can be used to construct unique DNA profiles (banding patterns) for every individual Using multiple ~ STR loci will enhance the reliability crime scene analysis and settling paternity disputes GENE CLONING The gene and a vector – plasmid – are isolated Amplified using PCR Both are cut with restriction enzymes and then joined using DNA ligase → recombinant plasmid The recombinant plasmid is isolated by gel electrophoresis and introduced into the target ~ cell The cell becomes genetically modified (transgenic) SEQUENCING – THE SANGER METHOD The base sequence of a DNA molecule can be determined using a modified version of PCR - the Sanger method Chain-terminating nucleotides (ddNTPs) - are incorporated into the reaction along with stocks of normal bases (NTPs) Four reactions occur – with a different ddNTP each time When the ddNTP is incorporated, DNA replication will stop - The fragment length is determined by the position of the base in the sequence (measured via gel electrophoresis) structure in nucleotide -change & MUTATIONS A gene mutation is a change in the nucleotide structure of a gene Mutations to a gene sequence may lead to changes in protein structure and function Substitution—one base in the coding sequence of a gene is replaced by a different base by chemical changes to bases or by mispairing during DNA replication Insertion—a nucleotide is inserted - an extra base in the sequence of the gene - requires a break in the sugar-phosphate backbone Deletion—a nucleotide is removed - one baseless in the sequence - two breaks in the sugar-phosphate backbone. CAUSES OF MUTATIONS ~ Proofreading Errors: Mutations can arise if an incorrect base pairing occurs during the - DNA replication process Mutagens: an agent that induces a permanent change to the genetic material of a cell - - Mutagenic exposure may harm cells and give rise to diseases Radiation increases the mutation rate if it has enough energy to cause chemical changes in DNA→Gamma rays, X-rays, alpha particles and short-wave ultraviolet radiation in sunlight Some chemical substances cause chemical changes in DNA, so are mutagenic→polycyclic aromatic hydrocarbons and nitrosamines found in tobacco smoke and mustard gas (a chemical weapon in the First World War) MUTAGENS Mutagenic agents may be either physical, chemical or biological in their origin - Physical: Certain forms of radiation (such as X-rays or ultraviolet) may trigger mutations - Chemical: Substances such as reactive oxygen species, certain metals, and alkylating agents - Biological: Some viruses (HPV) and certain bacteria (H. pylori) may induce mutations & POINT MUTATIONS Point mutations involve the modification of a single nucleotide within a base sequence Examples of point mutations include base substitutions and frameshift mutations BASE SUBSTITUTIONS Base substitutions involve the replacement of one base with another in the DNA sequence Silent (same-sense) mutation: The base substitution does not change the amino acid Missense mutation: The base substitution changes one amino acid (e.g. sickle cell anemia) Nonsense mutation: The base substitution creates a STOP codon FRAMESHIFT MUTATIONS - Frameshift mutations involve the addition (insertion) or removal (deletion) of a single base This changes the reading frame - every codon after the mutation will be altered Frameshift mutations typically have large impacts on protein structure and function BRCA1 BRCA1 is referred to as a tumor suppressor gene, it ~ repairs DNA - can mend double-strand breaks, and helps to correct mismatches in base pairing Mutation: - increased risk of other mutations due to the lack of DNA repair - increased risk of tumor formation and cancer - breast, ovarian, and prostate cancer. MUTATION OUTCOMES In multicellular organisms, mutations can be classified as either somatic or germ-line according to the cell affected Somatic Mutations: - Occur in a single body cell and cannot be inherited - - May give rise to cancers (uncontrolled cell division) GENETIC VARIATION Mutations are the only source of new alleles in a population increases genetic variation Genetic diversity functions to promote species survival within a changing environment - Without mutation, genetic variation in a population would decline over time, making natural selection impossible. This inevitably leads to extinction when the environment changes and the population cannot adapt and evolve. SEXUAL LIFE CYCLE Gametes (sex cells) are haploid – one copy of each chromosome pair The formation of haploid cells involves a meiotic division When two haploid gametes are fused, the resulting zygote will be diploid and can undergo mitosis to form more cells Sexual reproduction forms genetically unique offspring > - combination of alleles GENOTYPE The - - combination of alleles inherited by a sexually reproducing organism Alleles are the alternative forms of a gene - Genotypes can be categorized as being either: Homozygous – Both alleles are the same Heterozygous – The alleles are different Males are classed as hemizygous (one copy) for genes on the sex chromosomes characteristics of a organisms T PHENOTYPE Phenotype describes the =observable characteristics of an organism These traits can be due to genotype or the environment (or due to a combination of both) When multiple distinct phenotypes exist for a trait, the variations are called- polymorphisms  · PHENOTYPIC PLASTICITY Phenotypic plasticity describes how physical characteristics can be altered by the the environment to suit particular conditions Change in gene expression levels Phenotypic plasticity does not involve a change in the genotype - and the changes may be reversible during an organism’s lifetime Shell size of freshwater snails Shells are formed via a process of biomineralisation Smaller shells develop around predators (less exposure) GENETIC CROSSES The principles of inheritance can be demonstrated through breeding experiments with plants Male plants produce pollen which must be transferred from the anthers to the stigmas of female plants This physical transfer can be easily manipulated to target breeding between specific plants Many plants can produce seeds in short periods, allowing for the rapid collection of data P generation – parents F1 – first filial generation (offspring F2 – second filial generation Gregor Mendel – did genetic crosses with pea plants in the 19th century  ⑳ PUNNET SQUARES Genetic crosses can be represented by Punnett squares 1. -A letter is chosen to represent- the gene or trait o Alleles are shown as capital and lowercase letters 2. Parental genotypes and phenotypes are determined 3. Parental gametes are organized into a Punnett grid 4. Offspring genotypes and phenotypes are calculated o Results are shown as ratios, fractions, or percentages now allels - interact MODES OF INHERITANCE Describes the way alleles interact to determine the phenotype The different possible modes of inheritance include: Complete dominance – One allele is expressed over another in a heterozygous individual Codominance – Both alleles are equally expressed within a heterozygous individual Incomplete dominance – Both alleles contribute to a blended phenotype in heterozygotes & Sex linkage – The gene is located on a sex chromosome (so traits will display a sex bias) gene on a The ratios established by crosses represent probabilities and may not mirror actual results sex chromosome COMPLETE DOMINANCE Complete dominance describes the expression of one allele over another within a genotype The allele that is expressed is the dominant allele – represented by a capital letter (B) The allele that is not expressed is the recessive allele – shown as a lowercase letter (b)  2 E PHENYLKETONURIA In humans, the amino acid tyrosine can be synthesized from phenylalanine (non-essential) This reaction involves a specific enzyme which is encoded by the dominant allele of a gene Individuals with recessive alleles (homozygous) cannot convert phenylalanine into tyrosine This results in a toxic build-up of phenylalanine in the blood and urine (phenylketonuria) phenylalanine impairs brain development, leading to intellectual disability and mental disorders - can be prevented by screening for PKU at birth and giving affected children a diet low in phenylalanine. GENE POOL I all gene of a indidual in sexually reproducing populat A gene pool is all the genes of all the individuals in a sexually reproducing population Evolution is changes in the gene pool over time A gene is a length of DNA, with a base sequence that can be hundreds or thousands of - bases long The different alleles of a gene have slight variations in base sequence - usually only one or a few o bases are different (e.g. adenine might be present at a particular position in one allele and o cytosine at that position in another allele) Positions in a gene where different bases can be present are called single nucleotide o polymorphisms (SNPs - snips) - within one gene, there can be many different positions with SNPs many different alleles of a gene in the gene pool - multiple alleles Each individual receives a maximum of two different alleles from the gene pool. CODOMINANCE IN BLOOD GROUPS The ABO blood groups are determined by three alleles that demonstrate codominance A and B blood are encoded by codominant alleles, while a recessive allele encodes O blood INCOMPLETE DOMINANCE Whereas codominance involves both characteristics being equally expressed in a phenotype, incomplete dominance involves the characteristics merging to form a blended phenotype An example of incomplete dominance can be seen in the flower colours of Mirabilis jalapa A cross between a dark pink flower and a white flower results in a light pink flower SEX LINKAGE Genes that are found on the sex chromosomes Females have two X chromosomes, males have one X and one Y Sex-linked conditions are typically X-linked dominant or recessive This is because there are very few genes on the Y chromosome X-linked traits show a sex bias as males are hemizygous (one allele) - X-linked dominant traits tend to be more common in women - X-linked recessive traits are more common in men (no carriers) A a o *Alleles are shown as superscripts on a sex chromosome (X or X ) to control clotting inability S HAEMOPHILIA Haemophilia is a genetic disorder whereby the body’s ability to control clotting is impaired It is an X-linked recessive condition, meaning that it will occur more frequently in males This is because males cannot be carriers and must express the recessive allele (if present) PEDIGREE CHARTS A pedigree chart maps the occurrence of a specific characteristic across several generations Generations are labelled with roman numerals, individuals are numbered according to age Men are represented as squares and females are shown as circles (shaded means affected) INHERITANCE PATTERNS POLYGENIC INHERITANCE Polygenic traits refer to characteristics controlled by multiple (I.e. more than two) genes As more genes contribute to the expression of the phenotype, the variation increases Polygenic inheritance coupled with environmental influences results in continuous variation The phenotypic distribution follows a bell-shaped curve (e.g. skin color in humans)