Why are we use Pre-chilled Slides in karyotyping?

The pre-chilled slides burst chromosomes faster during the karyotyping. 

If you are here, trust me you haven’t found any sustancial answer for why the ‘the pre-chilled’ slides?

I can imagine that you want to optimize your karyotyping protocol rather than performing it, which means you are not looking for steps and procedures of how the karyotyping is performed. 

Before understanding the importance of it, let me tell you, the use of pre-chilled slides in cytogenetics is a very optimized thing! Only experts know about it. So first of all congratulate yourself. You are actually becoming an expert in karyotyping! Because you are searching on the internet why the pre-chilled slide is used during karyotyping. 

Before explaining why! Let’s make an introduction and then we will go further. 

Related article: What is Karyotyping?- Definition, Steps, Process, and Advantages.

A karyotyping is performed to get chromosomes and find out anomalies associated with it. Sample collection, cell culture, harvesting and microscopy are the steps common in karyotyping and hence it is a time consuming and tedious process. 

We need to invest at least 3 days time to get a well spread chromosome. But in the process, no metaphase, no separation of chromosomes and cell contamination are the common problems of karyotyping that occur routinely. 

Optimizing the karyotyping process is needed in day by day life because it’s not so robust. The whole process needs a contamination free zone or the sterile area. The major reason for failure in karyotyping is the contamination. 

But besides it, there are so many other factors that are responsible for poor karyotype. 

For example, suppose if culture media is not good enough! We will not get chromosomes. If Hypotonic treatment is not given properly, you may get metaphase but do not get chromosomes. 

So things like that must have to optimize properly and correctly before performing crucial karyotyping experiments. 

Now let’s jump directly to the microscopy section because we want to understand why chilled slides are used! To perform the microscopic analysis we need to prepare a chromosomal slide. 

To do so we need to stain it first and fix it on the slide.Giemsa staining method is so common in staining chromosomes. 

To observe chromosomes properly we need to separate it and fix it on the slide. A good chromosomal slide has three distinct properties viz, the bursted chromosomes, separated chromosomes and fixed chromosomes. 

We need to perform three different processes to achieve these properties which is very crucial, indeed.

By dropping the cell suspension from some height chromosomes separates well. 

By using the pre-chilled slide, a cell burst immediately and by heating the slide followed by chilling, chromosomes may fix faster on slide. 

The mechanism of pre-chilled slide is that when the swollen cells come in contact with the extreme chill, the cell membrane breaks immediately and chromosomes get separated. 

The entire process occurs within a fraction of a second.

So using a pre-chilled slide makes beautifully separated chromosomes. 

Preparing a pre-chilled slide:

Add 70% methanol into a beaker. 

Wide the slides with alcohol and dip into the methanol. 

Put the beaker in the deep freeze at -40C for 24hours. 

Take a slide drop cell suspension and heat it. 

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The use of pre-chilled slides in karyotyping is controversial, some scientists are in favor while some are not. As per my personal experiences, I had noticed substantial differences in the results with non pre chilled or pre-chilled slides.

It doesn’t mean that if we don’t use the pre-chilled slide, we will not get results but you will get less separated metaphase fields compared to using a pre-chilled slide. 

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