Genetics is the study of how traits are inherited from one generation to the next. Genes, the primary object of study in genetics, is made of DNA. While our generation has seen extraordinary advances in the science of genetics, it is actually a relatively young field. Indeed, the pattern according to which traits are inherited were initially described around 150 years ago. It was not even until the 1950s that DNA was understood.
Let us look at the four major branches of genetics:
1) Classical/Mendelian Genetics - this branch describes inheritance patterns. It describes how traits are passed from one generation down to another. Focusing primarily on individuals and their families, it mainly studies their phenotypes. Known alternatively as "transmission" genetics (because it studies trait inheritance), classical genetics, or Mendelian genetics, so-named because it was founded by gardener-monk Gregor Mendel, who described inheritance patterns.
2) Molecular Genetics - this involves the study of DNA, RNA, proteins, and how genes perform their functions. While classical or Mendelian genetics focuses on phenotypes, molecular genetics focuses on the underlying structural mechanics of the genes which give rise to our traits, such as the double helix or how gene expression involves copying DNA messages into RNA, which then "translates" the former and so on, in a manner comparable to how a blueprint is used to construct a racecar bed. Molecular genetics also entails the study of how genes can be turned on and off; a process known as "gene expression."
3) Population Genetics - this involves the study of the genetic constitutions of larger groups. This is Mendelian genetics writ large, as it focuses on inheritance patterns of several individuals within a specific geographical region in an attempt to identify their genetic signatures, patterns and vicissitudes, such as mutations, effect of environmental changes on selective pressures, comparison and contrasts from other isolated groups, the selective pressures which caused various groups to produce certain traits, and so on.
4) Quantitative Genetics - this involves looking at the statistical relationships between genes and the traits to which they produce. Using highly complicated statistical procedures, the quantitative geneticist attempts to determine the extent to which variation of a specific trait is due to the environment vs. how much is due to genetics. This helps us to determine how heritable a specific trait is, and can aid us in determining how to treat certain diseases which may require a certain underlying genetic predisposition to manifest itself.
For example, if a psychopathic personality is largely heritable, genetic testing may help us to raise such high-risk subjects in a specialized manner in order to properly direct the trajectory of their development and prevent them from becoming psychopathic.
Robinson, Tara Rodden (2010-04-13). Genetics For Dummies (Kindle Location 679). Wiley. Kindle Edition.