Atrait, such as height, has high heritability because much of the variation between individuals is the result of genetic variation. however, not all of the variation for height in a population can be attributed to genetic variation alone. why does genetic variation not always determine the differences in a given trait between individuals?

The differences in a given trait among the individuals can also be determined due to the changes in the environment that may change the expression of genes.  

The condition is categorized under epigenetics, it refers to the examination of variations in a species resulting due to modification of gene expression rather than the change of the genetic code itself. In other terms, it can be illustrated as an inheritance by mechanisms other than via the DNA sequence of genes.  

it would lead to upper respiratory infections and pneumonia.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.