There are lots of abnormalities when it comes to chromosomes, so you can pick out a few prominent sydromes that share similar detection methodologies and give a brief summary on the cause of the syndromes and then talk about the technologies used to detect them.
A few examples that I can think of as of now are:
Down syndrome, Turner's syndrome, Klinefelter syndrome. If you do a bit of research then I am sure you can find more

Methodology:
You should look up the following techniques- FISH (fluorescent in situ hybridisation) & Karytotyping.
Let me know if you've got ne more questions.
