|MadSci Network: Genetics|
You ask how crossbreeding is done generally, and say that any organism would do. But that actually makes it harder to answer, because the details do vary from one organism to another.
First off, I assume you mean plants, rather than animals, so I will talk about plants. (If you do want to know about animals, ask again.)
To crossbreed, or hybridise, two varieties of plants you need to make sure that pollen, the male bit, from one plant reaches the stigma, part of the female bits, of another. You also need to make sure that no other pollen apart from the one you supply can reach the stigma.
In some plants, it is quite easy. In corn, for example, the tassels at the top of the plant are the male part, while the silks that come out of the ears are the stigmas. You can collect pollen by putting a paper bag over the tassels. And you can stop other pollen getting to the silks by putting a bag over the ear. Then you pour the pollen you collected over the silks and close the bag again.
Pumpkins and squashes are also quite easy, because the male and female flowers are separate. But things like wheat and tomatoes and peas are much more difficult. In these plants, a single flower has both male and female parts. So you have to remove the male parts from the “mother” flower before adding the pollen from the “father”. The pollen may be transferred with a fine paintbrush.
After the cross has been made it is important to label the mother flower with the details, so that when you come back to collect the seed you will know which parents were used.
A very good book about all this is Breed Your Own Vegetable Varieties, by Carol Deppe. http://www.chels eagreen.com/Garden/BreedYourOwn.htm
I hope that helps. It can be hard to describe in words things that are easy to demonstrate and show in pictures, but I wasn’t able to find any good pictures on the internet.
Science Writer, International Plant Genetic Resources Institute.
Try the links in the MadSci Library for more information on Genetics.