If a trait is lowly heritable, does that mean that it cannot be improved genetically?
Traits with a low degree of heritability can still be improved genetically, though not as rapidly as more highly heritable traits. The rate of genetic progress is not controlled by heritability alone; the amount of observable (phenotypic) variation and the accuracy with which the variation can be identified are also key factors.
How many genes are responsible for the expression of economically relevant traits?
We do not yet know exactly how many genes impact economically relevant traits, but research indicates that many genes are likely to have small- to moderate-sized effects on performance for any given trait.
Are the effects of DNA markers the same for different breed sub-populations around the world?
Often they are similar, although the more divergent or distant a population is from another, the greater chance there is for the effect of markers to vary.