Karyotyping for Chromosomal Abnormalities

 Karyotyping for Chromosomal Abnormalities 

Each chromosome pair viewed in a karyotype appears to have its own distinct "bar code" of  bands. What changes do scientists look for in a karyotype when diagnosing diseases and  disorders? 

Karyotyping is process of pairing and ordering all the chromosomes of an organism, thus providing a genome wide snapshot of an individual's chromosomes. IT prepared using standardized staining procedures that reveal  characteristic structural features for each chromosome.  

Clinical cytogeneticists analyze human karyotypes to detect gross genetic changes—anomalies involving several  mega-bases or more of DNA. Karyotypes can reveal changes in chromosome number associated with aneuploid  conditions, such as trisomy 21 (Down syndrome). Careful analysis of karyotypes can also reveal more subtle  structural changes, such as chromosomal deletions, duplications, translocations, or inversions. In fact, as medical  genetics becomes increasingly integrated with clinical medicine, karyotypes are becoming a source of diagnostic  information for specific birth defects, genetic disorders, and even cancers. 

heterochromatic regions, which tend to be AT-rich DNA and relatively gene-poor, stain more darkly in  G-banding. In contrast, less condensed chromatin—which tends to be GC-rich and more transcriptionally  active—incorporates less Giemsa stain, and these regions appear as light bands in G-banding. Most importantly,  G-banding produces reproducible patterns for each chromosome, and these patterns are shared between the  individuals of a species. 

USING KARYO-GRAMS TO DETECT CHROMOSOMAL ABNORMALITIES  

Today, G-banded karyo-grams are routinely used to diagnose a wide range of chromosomal abnormalities in  individuals. Although the resolution of chromosomal changes detectable by karyotyping is typically a few  megabases, this can be sufficient to diagnose certain categories of abnormalities.  

For example, aneuploidy, which is often caused by the absence or addition of a chromosome, is simple to detect  by karyotype analysis. Cytogeneticists can also frequently detect much more subtle deletions or insertions as  deviations from normal banding patterns. Likewise, translocations are often readily apparent on karyotypes.

Reference  

• Caspersson, T., Zech, L., & Johansson, J. Differential banding of alkylating fluorochromes in  human chromosomes. Experimental Cell Research 60, 315–319 (1970) doi:10.1016/0014- 4827(70)90523-9 

• Speicher, M. R., Ballard, S. G., & Ward, D. C. Karyotyping human chromosomes by combinatorial multi-fluor FISH. Nature Genetics 12, 368–375 (1996) 

(https://www.nature.com/scitable/content/Karyotyping-human-chromosomes-by combinatorial-multi-fluor-14585/)

By: Abd El-Rahman Fareed