Posted: Wednesday, September 21, 2011 5:02 pm
Our parents and grandparents bequeathed certain physical attributes to us, perhaps in the form of a family resemblance or a special musical talent. Our parents also gave us a cellular time machine that allows us to trace our ancient ancestors. This time machine has two parts: a “Mommy Signature” and a “Daddy Signature.” Here is some background by way of analogy.
You have a unique book of instructions making you, well, you, unless you have an identical twin. Your book is written with a very limited alphabet – only four letters — where one “letter” represents one DNA base. Over 3 billion letters are in your book. This complete “book of instructions” is your personal genome.
Parts of your instruction book can be turned off (or on) by things such as smoking, exercising, stressing out, viral exposure, medication and so on. Over time these factors render identical twins not so identical after all.
Think of it this way. The letters in our instruction book can be arranged into “words” (genes) and those words can be arranged into meaningful “sentences” (proteins), after some biological editing and translating. Proteins are the workhorses of the cells.
Alphabetically speaking, each cell in your body has the same full set of instructions. Some cells turn into a heart and some cells turn into an eye. This amazing orchestration is accomplished by “reading” or skipping over certain words of the DNA instruction book in utero.
There are some funky aspects to the words and sentences found in your book. Reading can go from the left or the right while jumping over clumps of letters altogether and even starting in different locations. The resultant meaning will be altered but the sentences can still “make sense.” Think how incredibly difficult it would be to create such a book and not end up with a big mess.
When your book went to print, there were some errors. For example, a few letters may have been left out here and there. Perhps sme wrds may not make sens and some sentnces r messd up no mattr whch way u try to read em but sometimes everything still reads perfectly.
Your book is organized into “chapters” (chromosomes), co-authored by both parents. Dad’s contribution to the last chapter determines a baby’s gender. If “It’s a boy!” then that last chapter contains special regions of DNA that pass down virtually unchanged from father to son, grandfather to father, from great-grandfather to grandfather, and so on. Let’s call this the “Daddy Signature.”
When the baby is male, Dad’s last chapter contains only 39 percent as many letters as when his last chapter determined that the baby is female. Wow, even at the genetic level males “talk” less!
By comparing the Daddy Signature for two men, scientists can identify the most commonly shared recent ancestor between them. Since a woman does not have a Daddy Signature, she must vicariously access it through DNA samples from her father or any directly related male paternal relative.
Mom’s legacy is in the mix, too. However, we have to jump out of the chapters into what I will call the preface of the book. Dad contributed nothing to this genetic preface; Mom wrote it all. This preface cradles the “Mommy Signature.” Mom got the DNA content for her preface from her grandma and grandma from her great-grandma, and all the way back for many thousands of years. Your “super granny” can be identified by changes in the preface between women. Both males and females have the “Mommy Signature.”
Next stop: How can these patterns in the signatures capture our embedded history?
Editor’s note: Nancy Miller Latimer has worked in scientific research and development for 27 years. She blogs at neuronalbeauty.blogspot.com. Published in The Messenger 9.21.11