Editing Cytogenetics (section)

===Karyotyping===
The routine [[chromosome]] analysis ([[Karyotyping]]) refers to analysis of [[metaphase]] chromosomes which have been banded using [[trypsin]] followed by [[Giemsa]], Leishmanns, or a mixture of the two. This creates unique banding patterns on the chromosomes. The molecular mechanism and reason for these patterns are unknown, although it likely related to [[replication timing]] and chromatin packing.{{cn|date=February 2024}}

Several chromosome-banding techniques are used in cytogenetics laboratories. [[Quinacrine]] banding (Q-banding) was the first staining method used to produce specific banding patterns. This method requires a fluorescence microscope and is no longer as widely used as [[Giemsa]] banding (G-banding). Reverse banding, or R-banding, requires heat treatment and reverses the usual black-and-white pattern that is seen in G-bands and Q-bands. This method is particularly helpful for staining the distal ends of chromosomes. Other staining techniques include C-banding and [[Nucleolus|nucleolar]] organizing region stains (NOR&nbsp;stains). These latter methods specifically stain certain portions of the chromosome. C-banding stains the [[constitutive heterochromatin]], which usually lies near the centromere, and NOR&nbsp;staining highlights the satellites and stalks of [[acrocentric chromosome]]s.{{cn|date=February 2024}}

High-resolution banding involves the staining of chromosomes during [[prophase]] or early [[metaphase]] (prometaphase), before they reach maximal condensation. Because [[prophase]] and [[prometaphase]] chromosomes are more extended than metaphase chromosomes, the number of bands observable for all chromosomes (''bands per haploid set'', bph; "band level") increases from about 300 to 450 to as many as 800. This allows the detection of less obvious abnormalities usually not seen with conventional banding.<ref>{{cite journal |last1=Geiersbach |first1=Katherine B. |last2=Gardiner |first2=Anna E. |last3=Wilson |first3=Andrew |last4=Shetty |first4=Shashirekha |last5=Bruyère |first5=Hélène |last6=Zabawski |first6=James |last7=Saxe |first7=Debra F. |last8=Gaulin |first8=Rebecca |last9=Williamson |first9=Cynthia |last10=Van Dyke |first10=Daniel L. |title=Subjectivity in chromosome band–level estimation: a multicenter study |journal=Genetics in Medicine |date=February 2014 |volume=16 |issue=2 |pages=170–175 |doi=10.1038/gim.2013.95 |pmid=23887773 |doi-access=free}}</ref>

====Slide preparation====
Cells from [[bone marrow]], blood, amniotic fluid, [[cord blood]], tumor, and tissues (including skin, [[umbilical cord]], chorionic villi, liver, and many other organs) can be cultured using standard cell culture techniques in order to increase their number. A [[mitotic inhibitor]] ([[colchicine]], [[colcemid]]) is then added to the culture. This stops cell division at [[mitosis]] which allows an increased yield of mitotic cells for analysis. The cells are then centrifuged and media and mitotic inhibitor are removed, and replaced with a hypotonic solution. This causes the white blood cells or fibroblasts to swell so that the chromosomes will spread when added to a slide as well as lyses the red blood cells. After the cells have been allowed to sit in hypotonic solution, Carnoy's fixative (3:1 [[methanol]] to [[acetic acid|glacial acetic acid]]) is added. This kills the cells and hardens the nuclei of the remaining white blood cells. The cells are generally fixed repeatedly to remove any debris or remaining red blood cells. The cell suspension is then dropped onto specimen slides. After aging the slides in an oven or waiting a few days they are ready for banding and analysis.

====Analysis====
Analysis of banded chromosomes is done at a [[microscope]] by a clinical laboratory specialist in cytogenetics (CLSp(CG)). Generally 20 cells are analyzed which is enough to rule out mosaicism to an acceptable level. The results are summarized and given to a board-certified cytogeneticist for review, and to write an interpretation taking into account the patient's previous history and other clinical findings. The results are then given out reported in an ''International System for Human Cytogenetic Nomenclature 2009'' (ISCN2009)..