vce biology unit 4 exam revision
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DESCRIPTIONVCE BIOLOGY UNIT 4 EXAM REVISION. Gary Simpson . Contents. Chromosomes, Genes and Alleles Structure of DNA Protein Synthesis – Transcription/Translation Genetic Code Cell Reproduction Mitosis Meiosis Karyotypes Inheritance at one gene locus Pedigree Analysis - PowerPoint PPT Presentation
VCE BIOLOGY UNIT 4EXAM REVISIONGary Simpson ContentsChromosomes, Genes and AllelesStructure of DNAProtein Synthesis Transcription/TranslationGenetic CodeCell ReproductionMitosisMeiosisKaryotypesInheritance at one gene locusPedigree AnalysisInheritance involving two gene lociVariation
MutationGenotype/Phenotype/ EnvironmentRestriction EnzymesRecombining DNAVectorsPolymerase Chain ReactionGene ProbesGel ElectrophoresisDNA ProfilesDNA SequencingApplications of Gene Technology
Chromosomes, Genes and AllelesChromosomes are composed of DNAGenes short pieces of DNAAlleles the alternate forms of a geneGene Classification genes are classified by whether they are structural, regulatory or homoeoticGene Activity embryonic stem cells are totipotent, that is all the genes can express themselves, as cells specialise genes become switched off and switched on and so the ability of cells to be cloned from specialised cells for other purposes does not exist.Structure of DNAComprised of a sugar unit and a phosphate molecule that forms the backbone of the double helix and nitrogen bases which join the two strands together. Adenine binds with ThymineCytosine binds with Guanine.
Protein SynthesisTranscriptionRNA polymerase attaches to a region of DNA and unwinds the double strand.nucleotides align with complimentary bases to form a single stand of pre mRNAthe introns are removed to form mRNAa methyl cap and a poly A tail are added to produce operational mRNAthe mRNA exits the nucleus via the nuclear pores.
Protein SynthesisTranslationThe operational mRNA travels to the Ribosomes within the cytosol.tRNA in triplets (anti-codons) carrying amino acids are attracted from the cytosol to bind with complimentary codons on mRNAAmino acids combine to form a protein.
DNARNASugar UnitDeoxyriboseOxyriboseNitrogen basesA, T, G, CA, U, G, CDouble/single strandDoubleSingleLocationNucleusMostly CytoplasmComparison of DNA and RNAProtein SynthesisSummaryDNA Complimentary Strand - ATG GTC GCC GGC AGA TGA DNA Template Strand - TAC CAG CGG CCG TCT ACT
mRNA - AUG GUC GCC GGC AGA UGA
tRNA - UAC CAG CGG CCG UCU ACU
Amino acid sequence - Start, Val, Ala, Gly, Arg, Stop DNA CodeSecond PositionFirst positionUCAGThird positionPheSerTyrCysUUPheSerTyrCysCLeuSerSTOPSTOPALeuSerSTOPTrpGLeuProHisArgUCLeuProHisArgCLeuProGluNArgALeuProGluNArgGIleuThrAspNSerUAIleuThrAspNSerCIleuThrLysArgAMethThrLysArgGValAlaAspGlyUGValAlaAspGlyCValAlaGluGlyAValAlaGluGlyGInformation exists in three base sequencesCode is not overlapping (bases are read 3 at a time)Code is universal (all organisms share the same nucleotides)Code is redundant (more than one codon can code for the same amino acid)Code is unambiguous (each codon only codes for one amino acid)Cell ReproductionMultiple cell organisms grow by cells copying themselves and dividing, this requires the copying of the DNA.
The Cell CycleG1 Phase cell growth prior to DNA replication.S Phase DNA replicationG2 Phase the cell prepares for division into twoM Phase Mitosis the nucleus dividesC Phase Cytokinesis the division of the two cells is completed.
MitosisMitosis occurs in all organisms that are actively growing. During this process one cell divides and produces 2 daughter cells that are identical to the parent cell. These cells have two complete sets of chromosomes and are therefore described as diploid or 2n cells.
MeiosisProcess that occurs in the gonads (ovaries and testes) to produce 4 haploid cells called gametes (eggs and sperm).Two stage process. First division is the same as mitosis (one diploid cell makes two diploid cells) the second division reduces the two diploid cells to four haploid cells.Prophase 1 highest potential for single gene mutation as the chromosomes are most fragile as they are copied. Metaphase 1 crossing over may occur during random assortment of chromosomes at the equator in preparation for independent assortment.
Mitosis v MeiosisMITOSISMEIOSISNumber of replications11Number of divisions12Number of daughter cells produced24Haploid/DiploidDiploidHaploidTypes of cells producedSomaticGametesKaryotypesA Karyotype is essentially a map of an individuals chromosomes. It is created by analysing a tissue sample.Tissue can be sampled using chorionic villus sampling, mouth swab, amniocentesis, sperm, mucous, skin, or hair samples.
Segregation of AllelesGregor Mendel developed a series of laws to explain the separation of alleles into different gametes.1st Law states that the two alleles separate into different gametes2nd Law states that the separation of alleles for one gene are independent of the separation of alleles for another gene.Inheritance at a single gene locusHomozygous two alleles identicalHeterozygous two alleles not identicalTest Cross used to determine the genotype of unknown individuals. One crosses an unknown individual with an individual known to be homozygous recessive.Inheritance at a single gene locusMonohybrid cross alleles of only one gene at a single locusPunnett Squares are used to determine the chance of each type of offspring occurring.
Mothers Allele 1 (A)Mothers Allele 2 (a)Fathers Allele 1 (A)AAAaFathers Allele 2 (a)AaaaInheritance at a single gene locusComplete Dominance the affect of one allele masks the affect of the other allele.For example, the Allele B for large noses is dominant to the allele b for small noses. 50% of the offspring will have large noses and the other 50% will have small noses.
Allele 1BAllele 2bAllele 1 bBbbbAllele 2 bBbbbInheritance at a single gene locusCo-dominance, two alleles are both dominant over a third.For example, in human ABO blood groups both A and B are dominant over type O blood.
PhenotypeGenotypeA Type BloodIA IA , IA iB Type BloodIB IB , IB iAB Type BloodIA IBO Type Bloodi iInheritance at a single gene locusIncomplete Dominance the affect of the two alleles are blendedFor example, if an allele for white flowers (W) is mixed with an allele for red flowers (R) then the offspring have pink flowers.
Allele 1 WAllele 2 WAllele 1 RRWRWAllele 2 RRWRWInheritance at a single gene locusLethal Alleles the presence of some alleles can cause the death of the individual, either as an embryo or before they reach reproductive age.Sex linkage is when a gene is found on either the X or Y chromosome, then it is said to be sex linked and its pattern of inheritance is different to autosomal loci.Pedigree Analysis
Autosomal recessive inheritanceThings to remember:For an individual to express an autosomal recessive trait both copies of the allele must be presentIf both parents affected then all offspring will also be affected.Recessive traits tend to skip generations with few individuals affected.
Autosomal dominant inheritanceThings to remember:For an autosomal dominant trait to be expressed only one copy of the allele is required.Usually present in each generation, many affected individuals.If the homozygous dominant condition is lethal the phenotypic and genotypic ratios will be different good exam trick!
X-linked recessive inheritanceThings to remember:Males only require one allele to express the trait, therefore more males than females will show the trait.Females require both alleles to show the trait.Heterozygous females are described as carriers of the trait
X-linked dominant inheritanceThings to remember:Any individual with the trait must have a parent with the traitFemales may be heterozygous and show the traitThis condition is much harder to detect, so again a good exam trick question!
Inheritance involving two gene lociIndependent assortment of chromosomes. If two genes are found on different chromosomes they are said to be inherited independently.
ABAbaBabABAABBAABbAaBBAaBbAbAABbAabbAaBbAabbaBAaBBAaBbaaBBaaBbabAaBbAabbaaBbaabbVariationContinuous and discontinuousPolygenesSources of variation include mutations, environmental influences, random fertilisations, independent assortment, crossing over during meiosis
Discrete VariationContinuousVariationMutationsMutations are a change in the DNA sequence that may or may not have a significant impact on the phenotype.Can occur naturally or caused by high temperatures, chemicals and radiationMutations can be responsible for new alleles and variations in the phenotype of a species.
Point MutationThis is caused by a change to one base:
Template DNATAC TTC ACG GCA ATC CGA
DeletionTAC (T)TCA CGG CAA TCC GA?
AdditionT(T)A CTT CAC GGC AAT CCG A??
SubstitutionTA(T) TTC ACG GCA ATC CGA
InversionTAC TTC A(GC) GCA ATC CGAChromosomal MutationThis is caused by a change to a complete chromosome or large part of it:Deletion whole chromosome or section of it removedDuplication whole chromosome or section of it duplicatedInversion a region of the chromosome is turned aroundTranslocation a region of one chromosome is added to another.Genotype and PhenotypeGenotype refers to the alleles carried by an individual. Eg BbPhenotype refers to the visible characteristic that an organism displays. Eg. Bb means Big nose.Environmental Influence on PhenotypeThe phenotype of an individual is the sum of the genotype and the effects of the environment.
Reverse TranscriptaseThis enzyme is used to make copy DNA (cDNA) from mRNA.As mRNA contains no introns only the coding regions of a gene it is very useful when inserting genes into other organisms.Restriction EnzymesRestriction enzymes, or endonucleases, are naturally occurring chemicals which can cut strands of DNA at known positions, called recognition sequences.They can produce blunt end cuts or sticky end cuts.RecombinationOnce a piece of DNA has been cut with a restriction enzyme then it can be recombined