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Human Genetics

 

             Human genetics.
            
             1839- cell theory Schleiden & Schwann.
             1859- particulate inheritance Mendel.
             1877- chromosomes observed Flemming.
             1900- blood groups discovered Landsteiner.
             1903- chromosomes carry genes Sutton.
             1908- inheritance of blood groups Ottenburg.
             1910- 1st genetic clinic- USA Davenport.
             1946- 1st genetic clinic- UK Roberts.
             1949- sex chromatin Barr.
             1953- DNA chromosomes in man Watson & Crick.
             1960- 1st chr. abnormality in man Tjio/Levan.
             prenatal sexing Riis & Frucks.
             1961- x- inactivation.
             genetic code Nienenberg.
             1970- 1st gene synthesised in vitro Khorana.
             1979- in vitro fertilisation Edward's & Steptoe.
             1985- genetic fingerprinting Jeffrey's.
             1993- 1st gene therapy Numerous authors.
             Genetic defects.
             1. mutations- changes in one or more bases in a chromosome. mutations may be -.
             -dominant (gene is expressed is the next generation).
             - recessive (several generations for expression).
             2. aneuploidy- changes in the number of chr.s within a cell. normal diploid number is 46. haploid is 23. any deviation has serious consequences for the individual.
             3. chromosomal aberrations.
             - deletion- whole or part of a chromosome is missing.
             - inversion- part of chromosomes broken out, flipped over and reinstated so that order of genes is incorrect.
             - translocation- parts of non-homologous chr.s are exchanged.
             all of these chromosomal abnormalities (aberrations) can affect any of the pairs of homologous non-sex determining .
             chromosomes (called autosomes), or the sex chromosomes which are designated X and Y. females have two X chromosomes ("XX"), whereas males have one x and oneY ("XY").
             the diploid chromosome number in man is 46- i.e. 44 autosomes plus pair is sex chr. (expressed as 44+XX in females and 44+XY in males). this is the number of chromosomes found i our somatic (body) cells.


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