Suppose you find a yellow piece of metal in a stream. How could you tell if it is real gold?

you can tell by:

Simply draw your gold across an unglazed ceramic plate, applying slight pressure. If you can see a gold mark on the ceramic once you've done this, then the gold is real. However if the mark is black then it is fake.

in situ hybridization has been widely used for research applications, including clinical cytogenetics, gene mapping, tumor biology and studies of chromosome evolution.

it is called the mitotic spindle