Medical brain notes 33

  Human Genetics - Karyotyping.   Karyotyping is a technique through which the complete set of chromosomes are separated from a cell and the chromosomes are lined up in a  karyogram . The term karyogram has now been replaced by another word called  Idiogram  referring to a diagrammatic representation of chromosomes.   The karyological studies are usually made during mitosis, though the chromosome structure and details can also be best done in meiotic preparations. It is much easier to obtain and prepare suitable mitotic cells. Mitosis also reveals the replicated chromosomes viz., sister chromatids. The diploid set of chromosomes in the eukaryotic cells has constant morphological (phenotypic) features such as number, size, shape. The chromosomes are identified by other features such as the secondary constriction, arm ratio, and banding pattern. The summation of all such characters, which identify a set of chromosomes is called  karyotyping .   Kary...

  Genetic Engineering  (Recombinant DNA Technology )   All living organisms are endowed with specific genetic information. With advancement that progressed in genetical science, many aspects of gene functions became obvious. The molecular functioning of genes revealed the central dogma that DNA in a eukaryotic cell undergoes tran-scription to synthesize RNA and the latter undergoes translation to produce protein (polypeptide). Even before the modern aspects of molecular genetics are discovered, the existence of mobile genetic elements (Transposons) were visualized by the geneticist Barbara Meclintock in her work on maize plant Zea mays in 1965. Genetic engineering deals with the manipulation of genes according to human will. A gene of known function can be transferred from its normal location into an entirely different cell or organism, via a suitable carrier or vector. The carrier may be a plasmid DNA segment of a bacterium or a virus. The gene transferred likewise start...

  Genetic Diseases   1. Sickle cell anaemia :   Sickle cell anaemia is a genetic syndrome caused by an autosomal mutant allele Hbs. In homozygous condition (Hb s  Hb s ), it causes the production of an abnormal haemoglobin called haemoglobin S. The normal haemolobin is designated as Hb A  (Hb A Hb A ). Sickle cell persons with the genotype HbsHbs suffer from a fatal haemolytic anaemia. The patient dies due to damaged heart, kidney, spleen and brain as a result of  clogged blood vessels or vascular obstruction. Persons with heterozygous genotype HbA Hbs are said to be carriers and they survive. 2. Thalassemia :   Thalassemia is an erythroblastic anaemia due to homozygous recessive gene expression in children. Two types of this disease viz., thalassemia major and thalassemia minor exist. The former is the severe form while the latter is its milder form. The homozygotes suffer from severe thalassemia while all heterozygotes suffer from milder thalassemia....

  Human Genome Project (HGP)   Human genome project involves the human genome programmes to understand the genetic composition and genetic instruction that make up a human. The human genome is nothing but the DNA that resides in every human cell. The location and composition of 30,000 (thirty thousand) genes in human have been identified by sequencing the genome. It is known that the genes carry the information for the synthesis of various proteins. These pro-teins take up different profiles such as enzymes, hormones and antigens, which are responsible for various physiological and biochemical functions. The completion of the human genome project, by determining the DNA sequence of all the 23 pairs of chromosomes is a turning point and a break through in biology and medicine.   Human gene bank / genome database   Human gene bank or the genome database is the collection of sequenced genes and cataloging of them for future use. They represent the fundamental data. ...

  Cloning   Cloning is an experimental technique wherein, a group of genetically identical organisms is produced. Cloning of various animals was has become possible due to knowledge gained in the field of developmental biology and developmental genetics. It helped a lot, to understand the genetic control over differentiation of cells and the development of multicellular organisms.   Differentiation :  In the development of multicellular animals the zygote   represents the progenitor cell of the future embryo. Multitudes of cells arise from mitotic divisions of the fertilized egg cell. These cells later become distinct cell types differing in form and function. This process is called differentiation.   In the 1950s two embryologists R.Briggs and T.King developed a technique called nuclear transplantation. The nuclei from frog egg cells are taken out with a micropipette (enucleation) and replaced with nuclei taken from the cells of an embryo the same animal. ...

  Transgenic organisms   Genetically Modified Organisms (GMOs)   In genetic engineering, the methods of gene transfer lead to the production of transgenic animals and plants. These are called genetically modified organisms. Transgenism has been recognized as one of the thrust areas of biotechnology.   Gene transfer Methods   The uptake of genes by the cells in animals is called  trans fection . The transfected cells are used for a variety of purposes such as 1. The production of chemicals and pharmaceutical drugs, 2. Study of structure and function of genes and 3. Production of transgenic animals of commercial value such as livestock animals and fishes. It is also called  molecular farming . In transfection, fertilized eggs/embryos or the cultured   cells are employed.   Transfer of genes to Fertilized eggs or embryos   The transfection of fertilized egg involves either the transfer of whole nuclei or whole chromosomes; or their fragment...