Fluorescent in situ hybridization FISH

The FISH technique is based on the discovery that labelled ribosomal ribonucleic acid (RNA) hybridises to acrocen-tric chromosomes (i.e. chromosomes that have a non-centrally located centromere, and therefore unequal chromosome arms) [7,8]. It involves a fluorescently labelled deoxyribonucleic acid (DNA) probe being hybridised to genomic DNA sequences and can be used to study a specific site on a chromosome. These specific probes can be hybridized not only to metaphase chromosomes but also incorporated directly onto fixed interphase nuclei of non-mitotic cells [9] (Fig. 16.3). Four main classes of FISH probes are now available: repetitive-sequence probes, whole genomic DNA probes, locus specific probes and chromosome specific painting probes [9]. FISH signals are visualised by fluorescence microscopy using a light source that illuminates the fluorescently labelled specimens.

Conventional high-resolution chromosome banding techniques can result in up to 1000 bands per genome; however, even at such high resolution, deletions, duplications or translocations are difficult to detect. FISH, however, can be used to determine the origin of marker chromosomes and to confirm numerical and structural anomalies. FISH probes can detect regions as small as 0.5 kb on metaphase chromosomes in contrast to only much larger regions (2-3 Mb) using conventional banding

Fig. 16.2 Aneuploidy screening using FISH.

Fig. 16.2 Aneuploidy screening using FISH.

Chorionic Villi Fish

Fig. 16.3 Chorionic villi obtained after CVS.

techniques. The increased resolution provided by FISH is particularly suited to the study of microdeletion syndromes (e.g. Prader-Willi and Miller-Dieker) because the size of the DNA region that has been deleted is often very small.

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Pregnancy Diet Plan

Pregnancy Diet Plan

The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.

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