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Ebook BRS Genetics: Part 2

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Ebook BRS Genetics: Part 2

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

Ebook BRS Genetics: Part 2ell undergoing mitosis.■Melotlc chromosomes are much more difficult to study because they can be observed only in ovarian or testicular samples. In th

e female, meiosis is especially difficult because meiosis occurs during fetal development. In the male, meiotic chromosomes can be studied only in a t Ebook BRS Genetics: Part 2

esticular 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 sui

Ebook BRS Genetics: Part 2

table for some kinds of studies. For example, chorionic villi or amniocytes from amniotic fluid are used for prenatal studies; bone marrow is usually

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

Ebook BRS Genetics: Part 2nexplained mental retardation, or any other suspected generic conditions.■Whatever the (issue 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 ot Ebook BRS Genetics: Part 2

her tissues can be grown without such stimulation.■Once a tissue has reached its optimal time for a harvest, colchicine (Colcemid) is added to the med

Ebook BRS Genetics: Part 2

ia, which arrests the cells in metaphase.■The cells are then concentrated, treated with a hypotonic solution, which aids in the spreading of the chrom

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

Ebook BRS Genetics: Part 2of methods (see below).■It is often preferable to use prometaphase chromosomes in cytogenetic analysis as they are less condensed and therefore show m

ore detail. In cytogenetic analysis, separated prometaphase or metaphase chromosomes are identified and photographed or digitized.■The chromosomes in Ebook BRS Genetics: Part 2

the photograph of the metaphase are then cut out and arranged in a standard pattern called the karyotype, or in the case of digital images, arranged i

Ebook BRS Genetics: Part 2

nto a karyotype with the assistance of a computer.II.STAINING OF CHROMOSOMESMetaphase or prometaphase chromosomes may be prepared for karyotype analys

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

Ebook BRS Genetics: Part 2mosomes are not required.94Chapter 10Chromosomal Morphology Methods95A.Chromosome Banding. Chromosome banding techniques are based on denaturation and

/or enzymatic digestion of DNA, followed by incorporation of a DNA-binding dye. This results in chromosomes staining as a series of dark and light ban Ebook BRS Genetics: Part 2

ds.1G-Banding. G-banding uses trypsin denaturation before staining with the Giemsa dye and is now the standard analytical method in cytogenetics.a.Gie

Ebook BRS Genetics: Part 2

msa staining produces a unique pattern of dark bands (Giemsa positive; G bands) which consist of heterochromatin, replicate in the late s phase, are r

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

Ebook BRS Genetics: Part 2chromatin. replicate in the early s phase, are rich in G-C bases, and contain many genes.2R-Banding. R-banding uses the Giemsa dye (as above) to visua

lize light bands (Giemsa negative; R bands) which are essentially the reverse of the G-banding pattern. R-banding can also be visualized by G-C specif Ebook BRS Genetics: Part 2

ic dyes (e.g., chromomycin A3, oligomycin. or mithramycin).3Q-Banding. Q-banding uses the fluorochrome ợuinacrine (binds preferentially to A-T bases)

Ebook BRS Genetics: Part 2

to visualize Q bands which are essentially the same as G bands.4T-Banding. T-banding uses severe heat denaturation prior to Giemsa staining or a combi

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

Ebook BRS Genetics: Part 2xide denaturation prior to Giemsa staining to visualize c bands, which are constitutive heterochromatin, located mainly at the centromere.B.Fluorescen

ce in situ Hybridization (FISH).■The FISH technique is based on the ability of single stranded DXA (i.e., a DNA probe) to hybridize (bind or anneal) t Ebook BRS Genetics: Part 2

o its complementary target sequence on a unique DNA sequence that one is interested in localizing on the chromosome.■Once this unique DNA sequence is

Ebook BRS Genetics: Part 2

known, a fluorescent DNA probe can be constructed.■The fluorescent DNA probe is allowed to hybridize with chromosomes prepared for karyotype analysis

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

Ebook BRS Genetics: Part 2ction of fluorescent DNA probes to a wide variety of different DNA fragments from a single chromosome.■The fluorescent DNA probes are allowed to hybri

dize with chromosomes prepared for karyotype analysis and thereby visualize many different loci spanning one whole chromosome (i.e., a chromosome pain Ebook BRS Genetics: Part 2

t). Essentially, one whole particular chromosome will fluoresce.D.Spectral Karyotyping or 24 Color Chromosome Painting.■The spectral karyotyping techn

Ebook BRS Genetics: Part 2

ique Is based on chromosome painting whereby DNA probes for all 24 chromosomes are labeled with five different fluorochromes so that each of the 24 ch

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

Ebook BRS Genetics: Part 2n analyze the different ratios and assign a pseudocolor for each ratio.

chapter10ChromosomalMorphology MethodsI.STUDYING HUMAN CHROMOSOMES■Mitotic chromosomes are fairly easy to study because they can be observed in any ce

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