Read the incorrect sentence. write three to five sentences explaining what kind of run-on sentence it is and how to revise it. my mother and father are both scientists, it must have been my distiny to become interested in biology.

One way to fix that sentence is to switch around the two phrases used; 'My mother and father are both scientists' and 'It must have been my destiny to become interested in biology.'

It must have been my destiny to spark an interest in Biology, as my mother and father are both scientists.

That's a way to fix that sentence used in your question.

Also, 'destiny' was spelled incorrectly.

This sentence may seem run on if you don't place a conjunction between the two phrases, or if the phrases are not switched.

If the sentence is to be used with a conjunction, it may end up like this

My mother and father are both scientists, so it must have been my destiny to become interested in biology.

Or, you may just use a period, to change the two phrases used into two separate sentences.

Like this;

My mother and father are both scientists. For that reason, it must have been my destiny to become interested in biology.

ALSO, as you can see above, I have added a few words to the last sentence. Those three words, 'For that reason', give closure to the two sentences.

Hope this helped!