How to find how many loci control a trait? (Quantitative Genetics)

Most of the phenotypic characteristics that distinguish different individuals within a natural population are not of the all or none variety associated with laboratory-bred mouse mutations like albino, non-agouti, brown, quaking, Kinky tail, and hundreds of others. On the contrary, easily visible human traits such as skin color, wavy hair, and height, as well as hidden traits such as blood pressure, musical talent, longevity, and many others each vary over a continuous range of phenotypes. These are “quantitative traits,“ so-called because their expression in any single individual can only be described numerically based on the results of an appropriate form of measurement. Quantitative traits are also called continuous traits, and they stand in contrast to qualitative, or discontinuous, traits that are expressed in the form of distinct phenotypes chosen from a discrete set. Continuous variation in the expression of a trait can be due to both genetic and non-genetic factors. Non-genetic factors can be either environmental (in the broadest definition of the term) or a matter of chance. In mice, it is relatively straightforward to separate genetic from non-genetic contributions through the analysis and comparison of animals within and between inbred strains. Variation in expression among individual members of an inbred strain must be caused by non-genetic factors. Furthermore, if one is convinced that all individuals are maintained under identical environmental conditions, then existing variation is likely to be the result of chance alone. #phenotypic #mutations #QUANTITATIVETRAITS #genetic #genetics #breeding #selectionGenetics #QuantitativeGenetics