In the latter part of the 1800s (after Mendel) further refinement of microscopes, techniques for preparing biological tissues, and countless hours of examination revealed the processes of cell division (mitosis). (Show kids a video of mitosis for review—google; mitosis video.) Beyond this, a strange thing was observed regarding chromosomes. They occurred in pairs! (See: “human chromosomes images” and have kids note the pairs.) These pairs are most significant in the following.
A few years later, the process of meiosis, cell divisions leading the formation of gametes (eggs and sperm) was revealed. (Show kids the following video. Technical terminology can be omitted; have kids focus on the overall behavior of chromosomes.
Finally, have kids contrast the behavior of chromosomes in meiosis with what Mendel had theorized about 30 years previously (above).
What is the conclusion?
Hopefully, kids will see the conclusion by themselves, but use Q & A if necessary. In meiosis, chromosomes perform exactly the movements that Mendel had predicted would be necessary to give the results he observed. Chromosomes must be or carry the units of heredity (genes)!
The importance of this revelation cannot be overemphasized. It was the first time a particular component within cells could be assigned a biological function. It was a major turning point in the science of biology. It issued in the field of biochemistry.