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VCE BIOLOGY UNIT 4 EXAM REVISION

VCE 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

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VCE BIOLOGY UNIT 4 EXAM REVISION

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  1. VCE BIOLOGY UNIT 4EXAM REVISION Gary Simpson

  2. 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 • Inheritance involving two gene loci • Variation • Mutation • Genotype/Phenotype/ Environment • Restriction Enzymes • Recombining DNA • Vectors • Polymerase Chain Reaction • Gene Probes • Gel Electrophoresis • DNA Profiles • DNA Sequencing • Applications of Gene Technology

  3. Chromosomes, Genes and Alleles • Chromosomes – are composed of DNA • Genes – short pieces of DNA • Alleles – the alternate forms of a gene • Gene Classification – genes are classified by whether they are structural, regulatory or homoeotic • Gene 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.

  4. Structure of DNA • Comprised 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 Thymine • Cytosine binds with Guanine.

  5. Protein SynthesisTranscription • RNA polymerase attaches to a region of DNA and unwinds the double strand. • nucleotides align with complimentary bases to form a single stand of pre mRNA • the introns are removed to form mRNA • a methyl cap and a poly A tail are added to produce operational mRNA • the mRNA exits the nucleus via the nuclear pores.

  6. Protein SynthesisTranslation • The 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 mRNA • Amino acids combine to form a protein.

  7. Comparison of DNA and RNA

  8. Protein SynthesisSummary DNAComplimentary Strand - ATG GTC GCC GGC AGA TGA DNATemplate 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

  9. DNA Code • Information exists in three base sequences • Code 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)

  10. Cell Reproduction • Multiple cell organisms grow by cells copying themselves and dividing, this requires the copying of the DNA.

  11. The Cell Cycle • G1 Phase – cell growth prior to DNA replication. • S Phase – DNA replication • G2 Phase – the cell prepares for division into two • M Phase – Mitosis – the nucleus divides • C Phase – Cytokinesis – the division of the two cells is completed.

  12. Mitosis • Mitosis 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.

  13. Meiosis • Process 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.

  14. Mitosis v Meiosis

  15. Karyotypes • A 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.

  16. Segregation of Alleles • Gregor 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 gametes • 2nd Law states that the separation of alleles for one gene are independent of the separation of alleles for another gene.

  17. Inheritance at a single gene locus • Homozygous – two alleles identical • Heterozygous – two alleles not identical • Test Cross – used to determine the genotype of unknown individuals. One crosses an unknown individual with an individual known to be homozygous recessive.

  18. Inheritance at a single gene locus • Monohybrid cross – alleles of only one gene at a single locus • Punnett Squares are used to determine the chance of each type of offspring occurring.

  19. Inheritance at a single gene locus • Complete 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.

  20. Inheritance at a single gene locus • Co-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.

  21. Inheritance at a single gene locus • Incomplete Dominance – the affect of the two alleles are blended • For example, if an allele for white flowers (W) is mixed with an allele for red flowers (R) then the offspring have pink flowers.

  22. Inheritance at a single gene locus • Lethal 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.

  23. Pedigree Analysis

  24. Autosomal recessive inheritance • Things to remember: • For an individual to express an autosomal recessive trait both copies of the allele must be present • If both parents affected then all offspring will also be affected. • Recessive traits tend to skip generations with few individuals affected.

  25. Autosomal dominant inheritance • Things 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!

  26. X-linked recessive inheritance • Things 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

  27. X-linked dominant inheritance • Things to remember: • Any individual with the trait must have a parent with the trait • Females may be heterozygous and show the trait • This condition is much harder to detect, so again a good exam trick question!

  28. Inheritance involving two gene loci • Independent assortment of chromosomes. If two genes are found on different chromosomes they are said to be inherited independently.

  29. Continuous Variation Discrete Variation Variation • Continuous and discontinuous • Polygenes • Sources of variation include mutations, environmental influences, random fertilisations, independent assortment, crossing over during meiosis

  30. Mutations • Mutations 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 radiation • Mutations can be responsible for new alleles and variations in the phenotype of a species.

  31. Point Mutation • This is caused by a change to one base: Template DNA TAC TTC ACG GCA ATC CGA Deletion TAC (T)TCA CGG CAA TCC GA? Addition T(T)A CTT CAC GGC AAT CCG A?? Substitution TA(T) TTC ACG GCA ATC CGA Inversion TAC TTC A(GC) GCA ATC CGA

  32. Chromosomal Mutation • This is caused by a change to a complete chromosome or large part of it: • Deletion – whole chromosome or section of it removed • Duplication – whole chromosome or section of it duplicated • Inversion – a region of the chromosome is turned around • Translocation – a region of one chromosome is added to another.

  33. Genotype and Phenotype • Genotype refers to the alleles carried by an individual. Eg Bb • Phenotype refers to the visible characteristic that an organism displays. Eg. Bb means Big nose.

  34. Environmental Influence on Phenotype • The phenotype of an individual is the sum of the genotype and the effects of the environment.

  35. Reverse Transcriptase • This 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.

  36. Restriction Enzymes • Restriction 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.

  37. Recombination • Once a piece of DNA has been cut with a restriction enzyme then it can be recombined with itself or with other strands of DNA using DNA ligase.

  38. Vectors

  39. Polymerase Chain Reaction

  40. Gene Probes

  41. Gel Electrophoresis

  42. DNA Profiles • Short Tandem Repeats (STR) are sections of non-coding DNA of between 2 and 5 bases which are inherited and are display distinctive patterns within families. • Variable Nucleotide Tandem Repeats (VNTR) are longer than 5 bases, but also display distinctive patterns within families.

  43. DNA Sequencing • It is possible to map the location of genes by determining the position of each nucleotide

  44. Applications • Medicine • Malnutrition • Agriculture • Conservation • Forensic Science

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