The elegant double-helical structure of deoxyribonucleic acid (DNA) shook the scientific world when it was proposed in April 1953 by James Watson and Francis Crick. The DNA you inherited from your parents contains all your genes—your genetic information.
失败和挫折是人生的一部分，它们让我们更加深刻地认识自己，也让我们更加珍惜成功的时刻。泪水不代表脆弱，而是勇敢面对挑战后的释放。你们已经做得很好了，现在，是时候抬起头，擦干眼泪，继续前进。
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.
