Please enable JavaScript.

Coggle requires JavaScript to display documents.

Genetics and DNA - Coggle Diagram

- - - - if mutations appear within a coding region of a protein-coding gene, the mutation may alter that specific sequence in multiple ways
        
        CONSEQUENCES OF POINT MUTATIONS WITHIN CODING SEQUENCE OF PROTEIN-CODING GENE
        Base Substitution:
        (i) silent - causes no change, even though nucleotide sequence changed
        (ii) Missense - changes one amino acid in polypeptide
        (iii) Nonsense - changes a normal codon to stop codon (shortens polypeptide)
        
        Addition of Single Base:
        (iv)Frameshift produces a different amino acid sequence
        
        SICKLE- CELL ANEMIA results from point mutation in beta- globin gene.
        
        occurs when valine residue replaces glutamic acid
        
        MUTATIONS IN NON-CODING SEQUENCE
        
        PROMOTER: can increase or decrease rate of transcription
        
        OPERATOR SITE: alter regulation of transcription
        
        TRANSLATIONAL REGULATORY ELEMENT: alter ability of mRNA to be translationally regulated
        
        SPLICE SITES: alter ability of pre-mRNA to be properly spliced
        
        INTERGENIC REGION: not likely to effect gene expression
  - - - mutations also can occur within somatic cells (at early or late stages of development)
        
        in general the earlier a mutation occurs during development = larger patch
  - - - COMMON CAUSES OF SPONTANEOUS GENE MUTATIONS
        (i) errors in DNA replication - mistake by DNA polymerase can cause point mutation
        (ii) toxic metabolic products - products of normal metabolic may be reactive chemicals such as free radicals that can alter DNA structure
        (iii) Changes in nucleotide structure - linkage between a purine and deoxyribose can spontaneously break or changes in base structure may cause mispairing during replication
        (iv) Transposons - small segments of DNA that can insert at multiple sites in genome; however if they insert into a gene they may inactivate it.
      - COMMON CAUSES OF INDUCED GENE MUTATIONS
        (i) Chemical Agents - chemicals can cause changes in DNA structure
        (ii) Physical Agents - such as UV light and x-rays can damage DNA
        (NOTE: in particular, radiation of short wavelength and high energy (ionizing radiation) is known to alter DNA structure)
  - - - large number of oncogenes have been found that encode proteins that function in signal transduction pathways involved in cell growth; cell division is regulated, partially by growth factors.
        
        a growth factor binds to a receptor resulting in receptor activation
        
        this stimulates an intracellular signal transduction pathway that activates transcription factors.
      - PROTO-ONCOGENE - a normal gene that, if mutated, can become an oncogene
        
        oncogene is a gene that has been altered in a way that causes it to be overexpressed or expressed in the wrong cell type
        
        2nd type of genes that promote cancer are tumour-suppressor genes
        
        functioning of a normal tumour suppressor gene prevents cancerous growth
        
        proteins encoded by tumour suppressor genes usually has 2 functions
        
        maintenance of genome integrity
        
        negative regulation of cell division
        
        some cases, proteins encoded by tumour suppressor genes prevent cell from advancing through cell cycle if an abnormality is detected.
        
        these are checkpoint proteins because their role is to check the integrity of the genome and prevent cells from progressing past a certain point in cell cycle
        
        INACTIVATION OF TUMOUR-SUPPRESSOR GENES
        (i) MUTATION
        
        mutation can occur within a tumour-suppressor gene to inactivate its function
        
        (ii) CHROMOSOME LOSS
        
        Chromosome loss may contribute to progression of cancer if the missing chromosome carries one or more tumour-suppressor genes
        
        (iii) EPIGENETIC CHANGES
        
        involve the changes in chromatin structure that alter gene expression without altering base sequence of DNA
      - some viruses are capable of causing cancer
        
        (i) Rous Sarcoma virus- causes sarcomas in chickens
        (ii) Simian Sarcoma Virus - causes sarcomas in monkeys
        (iii) Abelson Leukemia Virus- causes leukemia in mice
        (iv) Hardly-Zuckerman 4 feline sarcoma virus- causes sarcomas in cats
        (v) hepatitis B- causes liver cancer in several species
- - - - RESTRICTION ENZYMES: an enzyme that recognises a particular DNA sequence and cleaves the DNA backbone at two sites
        
        BENEFITS OF RESTRICTION ENZYMES
        
        protect bacterial cells from invasion of viruses by degrading viral DNA into smaller fragments
        
        these enzymes bind to specific base sequences and then cleave the DNA backbone at two defined locations (on each strand)
        
        most recognise sequences that are palindromic (sequence is identical when read in opposite directions)
        
        EXAMPLES OF RESTRICTION ENZYMES USED IN GENE CLONING
        
        EcoRI: Escherichia Coli
        sequence: 5' - GAATTC - 3' -> 3' - CTTAAG - 5'
        
        Sacl: Streptomyces achromogenes
        sequence: 5' - GAGCTC - 3' -> 3' - CTCGAG - 5'
        
        BamHi: Bacillus amyloliquefaciens H
        sequence: 5' - GGATCC - 3' -> 3' - CCTAGG - 5'
        
        Pstl: Providencia stuartii
        sequence: 5' - CTGCAG - 3' -> 3' - GACGTC - 5'
        
        RECOMBINANT VECTOR: a vector containing a piece of chromosomal DNA
        
        GEL ELECTROPHORESIS: Technique for separating macromolecules (DNA and Protein) as they travel through a gel
        
        GENE EDITING: Molecular technique to alter the base sequence of a gene
        
        CRISPR- Cas Technology: technique used to introduce mutations into genes
  - - - TEMPERATURES FOR PCR
        
        DENATURING : 95
        
        ANNEALING 55-68
        
        EXTENSION 72
      - PCR requires THERMOSTABLE DNA polymerase enzyme
- - - - Karyotype reveals the number, size and form of chromosomes found in actively dividing cells
        
        Chromosomes being viewed actively dividing have already replicated
        
        the two copies are still joined (pair of sister chromatids)
        
        SISTER CHROMATIDS- two duplicated chromatids that are still joined to each other after DNA replication
        
        Eukaryotic cells that are meant to divide progress through the cell cycle, which involves a series of changes involving growth, replication and division
        
        ultimately the goal is to produce new cells
        
        cell cycle is highly regulated process to ensure cells divide at the correct time
        
        MIOTIC CELL DIVISION - process whereby eukaryotic cell divides to produce two new cells that're genetically identical to the original cell
        
        CENTROMERE - region where two sister chromatids are tightly associated
        
        it is an attachment site for kinetochore proteins
        
        SPINDLE APPARATUS- or mitotic or meiotic spindle Is the structure responsible for the organisation and sorting of eukaryotic chromosomes during cell division
        
        mitosis is a sorting process for dividing one cell nucleus into two nuclei
        
        MEIOSIS- the process by which haploid cells are produced from a cell that was originally diploid
        
        meiosis begins after cell has advanced through G1, S and G2 phases of cell cycle
        
        at beginning of meiosis 2 key events occur
        
        homologous pair of sister chromatids associate with each other, lying side by side forming a BIVALENT or tetrad
        
        the process of forming a tetrad is synapsis
        
        in most eukaryotic species they have a protein called synaptonemal complex which connects homologous chromosomes during meiosis
        
        second event that occurs is crossing over , which involves a physical exchange of genetic material between chromosomes segments of the bivalent
        
        DNA replication occurs prior to mitosis and meiosis I, but not in between meiosis I and II
        
        during prophase of meiosis I, the homologs bind to each other and form bivalents (explains why crossing over occurs during meiosis mostly)
        
        during prometaphase of mitosis and meiosis II, pairs of sister chromatids are attached to both poles; unlike meiosis I, each pair of sister chromatids is attached to a single pole
        
        at anaphase of meiosis I, homologous chromosomes separate, but the sister chromatids remain together; unlike sister chromatid chromatid separation occurring during anaphase of mitosis and meiosis II
        
        sorting occurs during meiosis I separates homologous chromosomes from each other - following meiosis I is followed by cytokinesis - and then meiosis II
        
        DNA replication doesn't occur between Meiosis I and II
        
        RECIPROCAL TRANSLOCATION- type of mutation where two different types of chromosomes exchange pieces which produce two abnormal chromosomes carrying translocation
        
        ANEUPLOIDY - alteration of the number of a particular chromosome present in an organism or cell. Total number of chromosomes is not an exact multiple of a set
- - - - when two individuals of the same species with different characteristics are bred together, the offspring are "hybrids"
      - single-factor cross: cross in which the experimenter follows the variants of only one character
        
        EXAMPLE: Mendel focused on tall and dwarf variants (height)
        
        Two Factor Cross: a cross which an experimenter simultaneously follows inheritance of two different characters
        EXAMPLE: dwarf and tall plants (height character), white and red leaves (colour character)
      - Punnett Square: method for predicting the outcome of simple genetic crosses
        
        Test Cross: is a cross to determine if an individual with a dominant phenotype is a homozygote or heterozygote; as well as determining if two different genes are linked
      - as cells prepare to divide, homologs replicate to produce pairs of sister chromatids
        
        Each Chromatid carries a copy of the allele found in original homolog (either T (DOMINANT) or t (RECESSIVE)
        
        During meiosis I, homologs containing sister chromatids, pair up and segregate&& into two daughter cells**
        
        one contains two copies of the dominant allele, the other has the two recessive copies
        chromatids separate during meiosis II
        
        thus produce 4 HAPLOID CELLS
        
        by the end each haploid cell has a copy of ONE of the TWO original homologs; two of the cells have a chromosome carrying the dominant allele and the other two have chromosomes carrying the recessive allele at the same locus
        
        MENDEL'S LAW OF INDEPENDENT ASSORTMENT - In meiosis I, two diploid heterozygous (TtRr) their chromosomes are replicated and the alignment of homologs occur in multiple ways in metaphase.
        
        two chromosome pairs lead to different combinations of alleles in the resulting haploids (EG: TR, Tr, tR, tr etc.)
        
        MENDELIAN INHERITANCE: inheritance patterns of genes that segregate and assort randomly
        
        SIMPLE MENDELIAN INHERITANCE- inheritance pattern of traits affected by a single gene that is found in two variants, one which is completely dominant over the other
        
        NORM OF REACTION: individuals with particular genotype exhibit under differing environmental conditions
        
        SEX CHROMOSOMES distinctive pair of chromosomes that differ in males and females in order to determine sex of individuals
        
        X-LINKED GENES: genes found on the X chromosome, but not the Y
        
        WILD-TYPE ALLELE- a prevalent allele in a population
        
        MULTIPLE ALLELES: gene has 3 or more alleles in a natural population
        
        INCOMPLETE DOMINANCE: heterozygote that carries two different alleles, exhibits a phenotype that is an intermediate between the phenotypes of the corresponding homozygous individuals