Well, we need to differentiate between genetic mechanisms and the role they play in natural selection.madscientist wrote:Hm interesting zoegirl about the changing in phenotypes. OK, but how does it happen? only phenotype changes, but no genotype? or does genotype change as a result? how can ph change just like that? and doesnt this get passed to next generations? somehow...
cos what causes this change in our genes to produce different hair color for example?
nurture having an effect on nature??
BTW noithing wrong so far with all this; isnt it looking kinda pro-evolutionist??
Phenotypes change because genes can be turned on and off. There are amazingly cool processes that are put in place to control what genes are transcribed and what proteins are made and even how long the mRNA molecules and proteins exist in the cell. From a foundational principle, this is true when you think about all of the different types of cells in our bodies. Muscle cells, nerve cells, intestinal cells, white blood cells, red blood cells, platelets all have (with the exception of mature red blood cells) the same genotype. They all have the same genes. (This is why they can clone animals with just using a body cell, all cells have the genetic capability of producing a new you). However, think about the fact that all of these cells have different genes turned on. You don't have skin cells secreting acid and stomach enzymes and stomach cells growing hair!! Because in each of these cells only the appropriate genes are turned on (in fact, much of what defines a cancerous cell is, is simplistic terms, a cell that has lost its identity.
Now, from an organism level, our phenotypes change throughout our lifetime because genes turn on and off. I already used the hair example. THere are plenty of examples of brown hair parents having a blond hair child who then develops brown hair. THis is simply an example of how complex gene interactions are. Some genes turn on other genes and these could be dependent of development or age of the organism. Reproductive capabilities is another example....when menopause starts, those genes regulating the mentrual cycle change....
Now even though genes are turned off they are still there. Independent assortment during meisosis assures that they will be passed down to some of the offspring. I have read that there is a facscinating new research into how the environment can methylate chromosomes and genes and affect how they function (this is sad that I cannot remember what they are calling the new area...I just read this last week...!! My poor memory!! ) Yay! EPIGENOME!! found it...here is a quick link http://www.wired.com/medtech/health/news/2005/08/68468
YOu also brought up the implications for evolution. I've never had a problem with microevolution or selection. Certainly there are plenty of examples in research showing population changes over generations. My skepticism comes with whether selection/microevolution has the power to generate such large scale changes as to then lead to the changes seen in accounts in earth's history.
As to the cancer/death....I doubt that selection, as nice and logical as that model sounds, can eliminate cancer and certainly, as was brought up already, death and decay are something that exists and doubt we can eliminate it....postpone it? MAybe.
Help?