Cloning of Animals
Although the cloning of Dolly the sheep in 1996 created a major furor in the media, from a scientific viewpoint it was a relatively small step in a developing …
Human Pedigree Analysis
Human matings, like those of experimental organisms, provide many examples of single-gene inheritance. However, controlled experimental crosses cannot be made with humans, and so geneticists must resort to scrutinizing medical …
Meselson–Stahl experiment
The first problem in understanding DNA replication was to figure out whether the mechanism of replication was semiconservative, conservative, or dispersive. In 1958, two young scientists, Matthew Meselson and …
DNA Replication
The copying mechanism to which Watson and Crick referred is called semiconservative. The sugar-phosphate backbones are represented by thick ribbons, and the sequence of base pairs is random. Let’s …
DNA: the genetic material
Before we see how Watson and Crick solved the structure of DNA, let’s review what was known about genes and DNA at the time that they began their historic …
Dormancy
During seed maturation , the embryo enters a quiescent phase in response to desiccation. Seed germination can be defined as the resumption of growth of the embryo of the …
Abscisic Acid
Unlike auxins, gibberellins, and cytokinins, the hormone abscisic acid(ABA) is represented by a single 15-carbon sesquiterpene. ABA also appears to have a more limited range of specific effects than …
Ethylene
During the 19th century, when coal gas was used for street illumination, it was observed that trees in the vicinity of streetlamps defoliated more extensively than other trees. Eventually …
Cytokinins
The cytokinins were discovered in the search for factors that stimulate plant cells to divide (i.e., undergo cytokinesis). Since their discovery, cytokinins have been shown to have effects on …
Gibberellins
Gibberellins are members of a large and varied family of plant constituents known as the terpenoids. Terpenes are normally recognized on the basis of their chemical structure, which may …