The number of cells in our bodies have been estimated to be about 37 trillion. However, that number is subject to much variation with legitimate estimates in a range from 5 to 724 trillion. For the purposes of this discussion, it is sufficient to say there are trillions of cells in the human body. Each one has the same complement of paired chromosomes with the same paired genes that control all of our traits. If all of those cells expressed all of their genes, we would have trillions of cells that were all the same. Yet we have many different kinds of cells all specialized to perform a certain set of the myriad of tasks needed to keep us alive. What prevents each gene from being expressed in each cell? How does a cell determine which genes to activate and which are not needed for its particular role. These differences are not caused by changes in the order of the nucleotides in the chromosomal DNA. However, they are inheritable. That is, they can be passed to daughter cells during mitosis and to sex cells during meiosis.
When a skin cell divides, two identical skin cells are created, the same goes for brain cells, liver cell, muscle cells, and so on. Epigenetics is the study of mitotically and/or meiotically heritable changes in gene expression that cannot be explained by changes in DNA sequence.
Because this website was originally intended for people using DNA testing to solve genealogical puzzles, I did not include any discussion of epigenetic (which was not nearly so well understood 15 year ago). However, over the years, the site has had many visitors from middle school, high school and college level students. In addition those years have seen tremendous advances in our understanding of epigenetics.
As I reviewed the video options for this topic on YouTube, I was overwhelmed with the plethora of interesting, factual, and well presented options. Epigenetic is a hot topic today. I have chosen a number of videos. The first and the last videos are longer than what I usually choose. But both are very well presented with excellent speakers. In spite of being longer, they do not go into much depth about the mechanisms of epigenetic. They will be easily understood by the layman. I recommend these videos for the genetic genealogists. They will be especially helpful in understanding the pitfalls of placing too much weight on physical similarities for adoptees or others who are looking for unknown biological relatives.
The second and third tabs hold videos that are shorter and are animations of mechanisms currently (sort of) understood to be a part of epigenetics. Tab three has three videos. If you are studying for an exam or preparing a presentation, watch these videos.
If you have the time, watch them all.