Jump to navigation Jump to search “AP Bio” redirects here. For the television series, see A. Advanced Placement higher biology essays course and exam offered by the College Board. 2013 school year, the College Board unveiled a new curriculum with a greater focus on “scientific practices.
This course is designed for students who wish to pursue an interest in the life sciences. The College Board recommends successful completion of high school biology and high school chemistry before commencing AP Biology, although the actual prerequisites vary from school to school and from state to state. In addition to the standard biology topics above, students are required to be familiar with a set of 12 specific biology labs, as well as general lab procedure. Students are allowed to use a four-function, scientific, or graphing calculator. Enter the characters you see below Sorry, we just need to make sure you’re not a robot. Enter the characters you see below Sorry, we just need to make sure you’re not a robot. This article may be too technical for most readers to understand.
Please help improve it to make it understandable to non-experts, without removing the technical details. Polymorphism in biology and zoology is the occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species. The term polyphenism can be used to clarify that the different forms arise from the same genotype. Polymorphism usually functions to retain variety of form in a population living in a varied environment.
The most common example is sexual dimorphism, which occurs in many organisms. According to the theory of evolution, polymorphism results from evolutionary processes, as does any aspect of a species. It is heritable and is modified by natural selection. In polyphenism, an individual’s genetic makeup allows for different morphs, and the switch mechanism that determines which morph is shown is environmental. The term polymorphism also refers to the occurrence of structurally and functionally more than two different types of individuals, called zooids, within the same organism. It is a characteristic feature of cnidarians. Although in general use, polymorphism is a very broad term.
A more specific term, when only two forms occur, is dimorphism. The use of the words “morph” or “polymorphism” for what is a visibly different geographical race or variant is common, but incorrect. The term was first used to describe visible forms, but nowadays it has been extended to include cryptic morphs, for instance blood types, which can be revealed by a test. Rare variations are not classified as polymorphisms, and mutations by themselves do not constitute polymorphisms. To qualify as a polymorphism, some kind of balance must exist between morphs underpinned by inheritance.
Polymorphism crosses several discipline boundaries, including ecology and genetics, evolution theory, taxonomy, cytology, and biochemistry. Different disciplines may give the same concept different names, and different concepts may be given the same name. For example, there are the terms established in ecological genetics by E. Various synonymous terms exist for the various polymorphic forms of an organism. The most common are morph and morpha, while a more formal term is morphotype. In the taxonomic nomenclature of zoology, the word “morpha” plus a Latin name for the morph can be added to a binomial or trinomial name. The white morph of the monarch in Hawaii is partly a result of apostatic selection.
Polymorphism is strongly tied to the adaptation of a species to its environment, which may vary in colour, food supply, and predation and in many other ways. Evelyn Hutchinson, a founder of niche research, commented “It is very likely from an ecological point of view that all species, or at least all common species, consist of populations adapted to more than one niche”. He gave as examples sexual size dimorphism and mimicry. The fitness of each type of mimic decreases as it becomes more common, so the polymorphism is maintained by frequency-dependent selection.
Thus the efficiency of the mimicry is maintained in a much increased total population. The mechanism which decides which of several morphs an individual displays is called the switch. This switch may be genetic, or it may be environmental. Taking sex determination as the example, in humans the determination is genetic, by the XY sex-determination system.
The polyphenic system does have a degree of environmental flexibility not present in the genetic polymorphism. However, such environmental triggers are the less common of the two methods. Investigation of polymorphism requires use of both field and laboratory techniques. Without proper field-work, the significance of the polymorphism to the species is uncertain and without laboratory breeding the genetic basis is obscure. Batesian mimicry noted in the nineteenth century are still being researched. In simple words, the term polymorphism was originally used to describe variations in shape and form that distinguish normal individuals within a species from each other.