(1) broad (H2): the proportion of total phenotypic variation in a particular trait at the population level that is attributable to variation in the 10 genotype;
(2) narrow (h2): the proportion of phenotypic variation that can be attributed to additive genetic variation, and which can be used to predict the response of the population to natural selection or selective breeding.
high density lipoproteins (HDL)
Molecular aggregates in the bloodstream consisting of about equal proportions of protein and lipid (i.e. 50 per cent protein and 50 per cent lipid, of which about two-fifths is cholesterol). HDL returns cholesterol to the liver where it is broken down to waste products that are excreted in bile. The proportion of HDL in the circulation is increased by the consumption of unsaturated fatty acids.
(noun: holism) A type of approach to describing or analysing a complex phenomenon, which takes account of all possible levels of explanation and their interactions; the phenomenon itself is considered as a ‘whole’ which is more than the sum of its component parts or influences.
The process of maintaining the stability of important internal variables and the instigation of corrective action when these deviate from optimum.
A chemical that is secreted into a blood vessel at one location and carried in the blood to effect action at some other site, which may be a large distance away.