What vegetable did mendel use in his experiments? what is the difference in a dominant and a recessive gene? what is a gene? what is an allele? what are genotypes? what are phenotypes?

Mendel used peas.
A dominant gene is a gene that will be the powerful one you could say. And a recessive gene is the weaker one. For example if D is blue (and dominant) and d was yellow (recessive) and you would get something like Dd then that off spring will blue not yellow, if that makes sense.
Genotypes are the letters I used like Dd, dd, DD.
And phenotypes are what the pair of letters respond to: Dd=blue, dd=yellow, DD= blue. Think of phenotypes as the how they will look physically. Hope this makes sense.

Type in the minus sign

It might. it might because if you think about if they discovered if we came from (lets say something funny like aliens) and thy found cells that matched and they would have t do more research about it but would most probably change their theory.