Levi is the oldest and most dominant gene. It's found all over the world and very common.
Wrangler is a gene mutation and seems to be more limited in range.. usually kept in free range situations also. Perhaps this gene is linked to better survival in rural situations?
Both are not sex linked and Levi is dominant over Wrangler. There are modifiers to those genes- main ones being zipper and button. Studies of genes have shown the zipper was the originial modifier but button has since become perhaps more common. Button seems to be dominant in association with the Levi gene, more ambiguous with the Wrangler gene, seems strongly recessive with Vanderbilt, however more gene studies need to be done on this.
With the widespread study and use of genes, especially by the young of each generation, more gene variations have been discovered and cultivated giving rise to gene types. Older new types are 'boot cut', 'straight fit' etc.. with more recent discoveries being called 'baggy', 'slim', 'skinny'. 'Relaxed fit' is dominant over these however current stock trend has been selection towards 'skinny'.
In the ancestral gene stock, color range was very limited- blue, black and very uncommonly, white. Newer colors have appeared- red, turquoise, yellow etc. Blue and black is dominant over all newer colors and remain the most common as a result.
Vanderbilt is a newer, sex linked gene. To date, no males of this gene has been discovered. Possibly sex linked lethal?