[michel_mr (OP)]

hello again,i am really dont understand how can we find the trisomy during karyotyping when we are using many cells not one?can u help me plzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz [?]

[WylieE]

Hi Michel,

  I'm not sure how it is done in animal cells, but for plant cells:  When one looks at the cells, they only look at one at a time, under a microscope, several cells are checked to make sure they all match up - from one individual they should all be the exact same. Sometimes it takes several cells to find even one where all the chromosomes are visible. 
 
  To automate things, in plants sometimes an instrument called a flow cytometer is used, in a process known as flow karyotyping.  This measures the fluorescence of each cell as it passes through the instrument.    Then this gives the average size of each chromosome for all the cells that it measures.

I hope this helps until someone who knows how it is done in humans can answer you better.