How are deviations from mendel's laws of inheritance explained?
The ratio mentioned in the law is the chance for each specific individual to get this trait or that. This applies to each individual separately, not to all of them as a group.
For example if the ratio is 50% dominant red color for a rose and 50% recessive white color, then there is a chance of 50% for every seed to get the genotype which results in a red color, and the other 50% is for the white one.
The second seed has the same chances.
If the the first seed gets the red color, this does not mean that the second one will be for sure white, it still has has the same two chances and it may get the re as the first one. It has the chance to be white, but this is not a must.