I've studied developmental biology, but I have not yet seen anything that explains how gametes actually "live". I think of DNA as the software of the cells. We know that gametes (sperm and unfertilized eggs) are alive and perform various functions; however, ...

 

• Has science uncovered how their DNA operates?
  
• Is their existence as gametes simply the "default" consequence of having only half of their DNA?
  
• Or (because gametes of diverse species behave very similarly) do gametes simply suppress their "organism" DNA/software (which runs after fertilization occurs)?
  
• So, do gametes (and, by extension, do all cells in our bodies) have two sets of software -- what might be called gametic and somatic?
  
• What especially puzzles me is that X sperm and unfertilized eggs seem to have the same DNA (ie, 23 chromosomes including an X sex chromosome), yet they develop and behave very differently. Why? How?
  

Edited December 25, 201015 yr by ewmon

In many ways gametes are not much different than other highly differentiated cells. Certain signals resulted in the activation of regulatory pathways that eventually led to the formation to their current state (i.e. gamete) and everything that is related to it (including no substantial cell growth etc.). This is true for about any cell type you find.

Essentially regulation is the key. This is even the case in unicellular organisms that do not differentiate. Up on certain cues (could be anything starting from nutrient availability, stress or quorum sensing), certain regulatory networks activate/deactivate leading to very different cellular responses, despite having the same genome.

Regulation. Thanks CharonY. It seems to work the other way too, because fertilized eggs don't grow flagella as sperm do, which means that the "gametic" genes are turned off after fertilization. Which leads me to my last point ...

 

What especially puzzles me is that X sperm and unfertilized eggs seem to have the same DNA (ie, 23 chromosomes including an X sex chromosome), yet they develop and behave very differently.

And the differences between X sperm and unfertilized eggs (ie, secondary oocytes)? Do they essentially have the same chromosomal components. There's size differences and also the sperm's flagella which the egg lacks. So it seems like it might be the hormonal/chemical environment the starter cells are in that differentiates them into sperm and eggs.

 

So, would an oogonium undergo spermatogenesis if transplanted into a male (or subjected to male hormonal levels), and likewise, would a spermatogonium undergo oogenesis if transplanted into a female (or subjected to female hormonal levels)? Or does differentiation go back further than that?

Edited December 26, 201015 yr by ewmon