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Transcript
Genetics for Statisticians MSc Course Duration: 18Hours, 6 x 3hour sessions Dates: Thursday 23rd May: 4:30-8:15 Thursday 30th May: 4:30-8:15 Thursday 6th June: 4:30-8:15 Thursday 13th June: 4:30-8:15 Thursday 20th June: 4:30-8:15 Presenters: Dr Samuel Murray BSc, Hons , PhD, MRCP Dr Fotios Siannis PhD Session Titles: 1. Genetics: The basics 2. Analytical methodologies and global standardisation issues [measures, cutoffs, ROC, EQA, sens/spec, reproducibility and requirements] 3. Biomarkers and their surrogates: integration into clinical medicine [prog/pred, designs – old v new v novel, case control, Harvey W Equilb, endpoints-RR, cross over, censorship] 4. Practical application and interpretation of large data sets: ‘Omics’ [design, interpretation, validation, algorithms] 5. Spotting methodological flaws, limitations of study design, multiplicity [p53, OncoDx, missing data, understanding the question, MA, post hoc] www.biology-resources.com/genetics 1 4 Cell 1 nuclear membrane cytoplasm In a cell which is not about to divide, the structures in the nucleus are not distinct 5 Cell 2 Just before cell division, thread-like structures appear in the nucleus 6 Cell 3 chromosomes These structures are called chromosomes They get shorter and thicker and take up stains very strongly 7 Cell 4 The shortening and thickening continues. Now the chromosomes are seen to be in pairs Chromosome pairs It may not be obvious from this illustration, but the chromosomes are always in pairs. They are distinguished by their size. 8 9 10 The chromosomes are always in pairs because one of them is derived from the male parent and the other from the female parent Different species have different numbers and shapes of chromosomes Members of the same species have identical sets of chromosomes Chromosome numbers kangaroo (6 pairs) chicken (18 pairs) 11 a sedge (21 pairs) hawkweed (4 pairs*) fruit fly (4 pairs) human (23 pairs) 12 Although chromosomes can be seen distinctly only at the time of cell division, they are present and active all the time The chromosomes carry the DNA DNA controls all the chemical reactions in the cell DNA also determines the species of organism and its individual characteristics 13 Chromosomes and DNA DNA chromosome protein double helix Chromosomes consist of DNA molecules supported by a ‘scaffold’ of proteins. The diagram illustrates such an arrangement but it is really more complex than this 14 The DNA in the chromosomes carries the genes Consequently, the genes are spaced out along the chromosome The genes consist of distinct stretches of the DNA By means of their DNA content, the genes control the activities of the cell, the type of cell it becomes, the species of the organism and the individual characteristics of that organism 15 Chromosomes and genes chromosome genes for hair colour single gene genes for tallness genes for eye colour The diagram illustrates the relationship between chromosomes and genes but it does not represent an actual chromosome. The genes for these characteristics are not necessarily on the same chromosome and the number of genes shown is arbitrary Chromosomes and genes A Because the chromosomes are in pairs, the genes they carry are also in pairs Each member of a pair of genes comes from either the male or the female parent just as the chromosomes do The individual genes of a pair, control the same characteristic, e.g. B and b could control eye colour; G and g could control hair colour a B b C c D d E e F f G g H h I I 17 Chromatids chromatids Just before cell division, it can be seen that the chromosomes have replicated; that is each chromosome has made a copy of itself (including its DNA). These copies and the originals are now called chromatids 18 Centromere The chromatids tend to separate but are held together by a special region called the centromere chromatids 19 The next sequence of slides shows the way the chromosomes are distributed during cell division For clarity, only two pairs of chromosomes are represented The chromosomes coloured blue are derived from the male parent; the chromosomes shown in red are from the female parent Cell division 1 20 Two pairs of chromosomes. Each chromosome has replicated to form chromatids Cell division 2 21 The nuclear membrane disappears Fibres appear in the cytoplasm and form a spindle The chromosomes move to the ‘equator’ of the spindle Cell division 3 22 The spindle fibres shorten and appear to pull the chromatids apart by their centromeres 23 Cell division 4 The chromatids are now chromosomes. The chromosomes migrate to opposite ends of the cell as the spindle fibres shorten Cell division 5 24 The cell begins to divide 25 Cell division 6 The nuclear membrane forms again The cell constricts The chromosomes become less distinct Cell division 7 26 Two cells formed The chromosomes revert to their elongated thin shape and eventually cannot be seen Each cell now has a full set of chromosomes identical to the parent cell Mitosis 28 This process of cell division, which produces cells containing identical sets and numbers of chromosomes, is called MITOSIS Mitosis ensures that every cell of an organism carries an identical set of genes Can you see a problem with this? 29 The problem is that if every cell carries the same set of genes, how do cells become specialised in shape and function to do different jobs? For example, what can a gene for brown eyes do in a stomach cell? The answer is that the genes which are not relevant to the cell’s function are not activated. We say the gene for brown eyes is not expressed in a stomach cell 30 Mitosis 1 2 3 7 4 6 5 31 The next slide shows a photomicrograph of onion root cells. In a root tip, a great many cells are dividing by mitosis, leading to rapid growth. The preparation is made by softening the root tip tissue, squashing it on a microscope slide and staining the chromosomes and nuclei. The ‘squash’ technique spreads the cells out. See if you can associate the various stages of cell division with the stages 1-6 in the previous slide. Bear in mind that the previous slide is a purely diagrammatic representation. 32 Root tip squash 4 1 7 4 2 5 © McLeish & Snoad Macmillan 33 Question 1 Staining techniques show up the nucleus because (a) The nucleus is enclosed in a nuclear membrane (b) Nucleus and cytoplasm have different chemical properties (c) The cytoplasm is less concentrated than the nucleoplasm (d) The nucleus is in the middle of the cell 34 Question 2 When are chromosomes present in the nucleus ? (a) Only just before cell division (b) Only during cell division (c) Only after cell division (d) All the time 35 Question 3 Chromosomes are in pairs because (a) They have replicated (b) Each is derived from either the male or female parent (c) They are joined at the centromere (d) They have to be shared at cell division Question 4 36 How many chromosomes are there in a human cell? (a) 100+ (b) 92 (c) 46 (d) 23 Question 5 Which of these statements are correct ? DNA controls (a) The species of the organism (b) The function of the cell (c) Features of the organism such as size (d) Chemical reactions in the cell 37 38 Question 6 Which of these statements are correct? A chromosome contains (a) Protein (b) Cellulose (c) DNA (d) Genes Question 7 The process by which a chromosome makes a copy of itself is called (a) Reproduction (b) Recombination (c) Relocation (d) Replication 39 Question 8 a b c d 40 e f What is the correct sequence of events in mitosis ? (a) c, d, a, b, e, f (b) b, c, a, d, e, f (c) c, b, a, e, d, f (d) c, b, d, a, e, f