Phenotype = Genotype x Environment + Hormones
PHENOTYPE = what we can see and measure in an individual.
GENOTYPE = inheritance.
ENVIRONMENT = all the environmental factors, natural and man made, that influence the expression of genotype.
HORMONES = balance between sex and growth hormones.
Therefore, what we can observe or measure in an individual is phenotype which is an expression of the interaction between environment and genotype and the modifying effect of hormones.
In order for selection to be representative of genotype (inheritance) we rely on phenotype where environmental differences (corrections) and hormonal influence are accounted for.
This is much easier than it appears IF one understands that the observed difference between individuals is dependent on all environmental influences and is modified by hormones.
If we can account for within herd environmental differences (eg. age, date of calving / birth, etc.) then the difference between individuals is an expression of genes and heritable.
The above two photos (Afrizebu) are indicative of harmony between genotype and environment and hormonal balance (sexual dimorphism.)
The above two individuals are an expression of different genotypes in the same environment.
Genetics has become so trivialized that most of us do not appreciate the value of genetics.
The above two Drakensberger bulls illustrate the modifying influence of hormones (testosterone) on size and masculinity.
The top bull has a fast absolute growth rate; the bottom bull has a fast relative growth rate.