Genes R US — Mom indelible genetic mark in son’s lifespan
Posted: Wednesday, August 8, 2012 5:00 pm
Last week an article, in the journal CELL, made headlines in the popular press. The Aussie scientists presented convincing evidence as to why females outlive males. The elegant scientific study was performed on … fruit flies. The results were then hypothetically extended to humans.
Across all species, females do tend live longer, all other things being equal. Regardless of your personal convictions regarding cross-species evolution, there is an undeniable preservation of many cell signaling pathways, including those responsible for aging and longevity in the animal kingdom, which includes us.
God had a brilliant way of encoding chemical intelligence with an infinite potential for diversity into the DNA of his creatures. And He saw that it was really good! Evolution (yes, even cross species) is a strong testimony to God’s creative fingerprints! Of course that implies a reading of the bible as the why and purpose of creation rather than a science book of how but that is another column … or maybe a book.
Back to fruit flies. Fruit flies are a geneticist’s best friend because of their (1) many similar cellular pathways to humans, (2) ease of breeding in captivity, and (3) short lifespan. The effect of tweaking the fruit fly genome and then observing the result across successive generations is very efficient. Thus fruit flies are called model organisms as are yeast, worms, mice, and rats.
In the study published last week, populations of fruit flies were genetically identical except they had received their mitochondrial DNA from different female lines. Mitochondrial DNA is distinct from the DNA in chromosomes that both parents contribute to equally. There is a whole separate genome for the mitochondrion.
Mitochondria live outside the cell’s nucleus, whereas, chromosomes live inside the nucleus. Mitochondria have lots of cellular chores. They create chemical energy; control how long a cell lives, and other cool things.
The mitochondria have their own “agenda” separate from that of the chromosomes. If the chromosomes introduce diversity within species then the mitochondria’s agenda is to keep things the same as dear ol’’ mom.
Sperm from mammals contain mitochondria but most of it hangs out it the tail in order to provide the maximal energy for the Olympic race to the egg. But the tail never makes it into the fertilized egg and any bit of male mitochondrion that should remain is destroyed by the developing embryo. The only surviving mitochondrial DNA is that which is found in the female’s egg.
Occasionally mutations will still sneak into mom’s mitochondria. But natural selection exerts pressure to keep those mutations which are either favorable or neutral to her and remove any that are deleterious to her. The same mutations can be deleterious to males and escape discovery and thus constructive genetic editing!
The mtDNA that is used to track one’s direct female ancestry is part of the mitochondrial genome-which may make more sense to you now.
People live longer than they did centuries ago, but there is no difference in extreme aging. Even with a literal reading of the bible, post the time of Noah, there has been no change in extreme aging. One hundred twenty years is pretty much the upper limit.
As of this week, of the 71 certified supercentenarians (aged 110 to 115 years old) still living: 67 of them are women; only four are men. (http://bit.ly/lls9v) Spending any time in nursing homes you will quickly observe that the majority of the oldest residents are always women.
Daughters are evolutionarily equipped to escape the genetic defects of their mother’s mitochondrial DNA-but not so for their sons.
How long a man lives is going to depend on lots of things in his environment, his behavior, and the complete genome that he received from both parents. But a man’s upper limit controlled by his mother’s curse, I mean gift of mitochondrial DNA.
Mom has the last genetic word. Would you expect it to be any different?
Nancy@NancyMiller Latimer.com has worked in scientific research and development for 27 years. She blogs at NeuronalBeauty.BlogSpot.com. Published in The Messenger 8.8.12