Codominance or incomplete dominance is the answer in this question. This pattern of color expression is most likely to be an example of incomplete dominance or codominance. Codominance is defined as a form of dominance wherein the alleles of a gene pair in a heterozygote are fully expressed. Incomplete dominance on the other hand is a form of intermediate inheritance in which one of the allele for a specific trait is incompletely expressed over its paired allele.
The "set-point theory" implies that each individual is genetically programmed to carry a particular amount of body weight.
The set point is the weight range in which your specific body is programmed to work. The set point theory trusts that a man's body will battle to keep up that specific weight range.
I think what they rely on is there experiment and how they do it
