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(BQ) Part 2 book "BRS Genetics" presents the following contents: Chromosomal morphology methods, cytogenetic disorders, genetics of metabolism, genetics of hemoglobinopathies, genetics of bleeding disorders, genetics of development, genetics of cancer, genetics of cancer, consanguinity. | I. STUDYING HUMAN CHROMOSOMES Mitotic chromosomes are fairly easy to study because they can be observed in any cell undergoing mitosis. Meiotic chromosomes are much more difficult to study because they can be observed only in ovarian or testicular samples. In the female meiosis is especially difficult because meiosis occurs during fetal development. In the male meiotic chromosomes can be studied only in a testicular biopsy of an adult male. Any tissue that can be grown in culture can be used for karyotype analysis but only certain tissue samples are suitable for some kinds of studies. For example chorionic villi or amniocytes from amniotic fluid are used for prenatal studies bone marrow is usually the most appropriate tissue for leukemia studies skin or placenta is used for miscarriage studies and blood for patients with dysmorphic features unexplained mental retardation or any other suspected genetic conditions. Whatever the tissue used the cells must be grown in tissue culture for some period of time until optimal growth occurs. Blood cells must have a mitogen added to the culture media to stimulate the mitosis of lympocytes but other tissues can be grown without such stimulation. Once a tissue has reached its optimal time for a harvest colchicine Colcemid is added to the media which arrests the cells in metaphase. The cells are then concentrated treated with a hypotonic solution which aids in the spreading of the chromosomes and finally fixed with an acetic acid methanol solution. The cell preparation is then dropped onto microscope slides and stained by a variety of methods see below . It is often preferable to use prometaphase chromosomes in cytogenetic analysis as they are less condensed and therefore show more detail. In cytogenetic analysis separated prometaphase or metaphase chromosomes are identified and photographed or digitized. The chromosomes in the photograph of the metaphase are then cut out and arranged in a standard pattern called the karyotype or
