Chromosomal inheritance can result in mutations that increase genetic diversity but can also cause genetic disorders. Sexual reproduction can increase genetic diversity by creating offspring with extra or missing chromosomes.
Another departure from simple Mendelian genetics arises when the phenotype for a character depends on environment as well as genotype.
In the 1900s, geneticists extended Mendelian principles not only to diverse organisms, but also to patterns of inheritance more complex than those described by Mendel.
Modern genetics began during the mid-1800s with a monk named Gregor Mendel, who discovered the basic principles of heredity by breeding garden peas in carefully planned experiments.
Gamete formation involves a type of cell division called meiosis. This type of cell division reduces the number of sets of chromosomes from two in the parent cell to one in each gamete, counterbalancing the doubling that occurs at fertilization.
Levels of proteins called cyclins increase and decrease during the cell cycle. Cyclins were discovered in studies of mitosis in sea urchin gametes.
Mitosis is just one part of the cell cycle, the life of a cell from the time it is first formed during division of a parent cell until its own division into two daughter cells
Negative feedback helps to maintain homeostasis. Positive feedback is self-reinforcing and amplifies responses.
Food and drugs can be sources of chemicals that act as exogenous ligands in cell communication. Exogenous ligands can disrupt the usual activity of a signal transduction pathway, thereby altering the responses of target cells.
Signal Transduction pathways differ in specific details, but have certain, unifying characteristics. All pathways follow a sequence: Reception，Transduction, Response
