Validity of an experiment is based upon:

it is based upon the correlation between the results of your measurements and the results of the criterion measurement.

I hope this helps

small, big, or no change could occur in the phenotype. it could cause something as simple as a cats ears to curl backwards or something as frighting as death. it could also occur in the protien-coding area and have an effect on that but no effect on the amino acids. what has to occur is a changing in the hox gene or the control gene.