PATHOPHYSIOLOGY
Pathophysiology is the study of the disturbance of normal mechanical, physical, and biochemical functions, either caused by a disease, or resulting from a disease or abnormal syndrome or condition that may not qualify to be called a disease. An alternate definition is “the study of the biological and physical manifestations of disease as they correlate with the underlying abnormalities and physiological disturbances.”
An example, from the field of infectious disease, would be the study of a toxin released by a bacterium, and what that toxin does to the body to cause harm, one possible result being sepsis. Another example is the study of the chemical changes that take place in body tissue due to inflammation.
Pathophysiology can be looked at as the intersection of two older, related disciplines: (normal) physiology and pathology.
Physiology is the study of normal, healthy bodily function (as opposed to anatomy, which is the study of normal structure). When something disrupts normal physiological processes, it enters the realm of pathophysiology.
Pathology, broadly speaking, is the “study of the nature and cause of disease.” or the results of disease in the body. Pathophysiology looks at the detailed malfunctioning that comes from or, alternately, causes disease.
One caution in this approach is that healthy structure and function is not precisely the same in any two individuals.
Pathophysiology is a required study for most nursing school programs in the United States as well as other countries.
GENETICS
Genetics is the science of heredity and variation in living organisms. Knowledge of the inheritance of characteristics has been implicitly used since prehistoric times for improving crop plants and animals through selective breeding. However, the modern science of genetics, which seeks to understand the mechanisms of inheritance, only began with the work of Gregor Mendel in the mid-1800s. Although he did not know the physical basis for heredity, Mendel observed that inheritance is fundamentally a discrete process with specific traits that are inherited in an independent manner — these basic units of inheritance are now called genes.
Following the rediscovery of Mendel’s observations in the early 1900s, research in 1910s yielded the first physical understanding of inheritance — that genes are arranged linearly along large cellular structures called chromosomes. By the 1950s it was understood that the core of a chromosome was a long molecule called DNA and genes existed as linear sections within the molecule. A single strand of DNA is a chain of four types of nucleotides; hereditary information is contained within the sequence of these nucleotides. Solved by Watson and Crick in 1953, DNA’s three-dimensional structure is a double-stranded helix, with the nucleotides on each strand complementary to each other. Each strand acts as a template for synthesis of a new partner strand, providing the physical mechanism for the inheritance of information.
The sequence of nucleotides in DNA is used to produce specific sequences of amino acids, creating proteins — a correspondence known as the “genetic code”. This sequence of amino acids in a protein determines how it folds into a three-dimensional structure, this structure is in turn responsible for the protein’s function. Proteins are responsible for almost all functional roles in the cell. A change to DNA sequence can change a protein’s structure and behavior, and this can have dramatic consequences in the cell and on the organism as a whole.
Although genetics plays a large role in determining the appearance and behavior of organisms, it is the interaction of genetics with the environment an organism experiences that determines the ultimate outcome. For example, while genes play a role in determining a person’s height, the nutrition and health that person experiences in childhood also have a large effect.

Related Reading:

The Stuff of Life: A Graphic Guide to Genetics and DNAThe Stuff of Life gives readers a complete introduction to the history of genetics that's as easy to understand as it is entertaining to read.