Gregor Johann Mendel was the first to visualize a gene as a discrete, stable particulate unit of inheritance in 1865. He called it a factor and postulated that the offspring receive some specific factors from their parents which make parents characters to appear in the offspring. The term “Gene” was introduced by Johansson in 1909 for a unit of heredity located at a specific site, the locus, in a chromosome. Continue reading What are Genes?
The continued secondary growth of vascular cylinder in many older roots and stems exerts a pressure which results in the stretching and rupturing of the epidermis, cortex and other tissues outside the secondary phloem. To avoid such breaking of external tissues, the plant organs develop a secondary protective covering by replacing epidermis and other external tissues. This protective secondary covering (tissues) of certain plants, especially woody plants, is called Periderm. Continue reading What is Periderm in Plants?
Swim Bladder, also called air bladder, is an expandable gas-filled sac that helps many bony fishes to control their buoyancy in order to stay at their current water depth without having to waste energy in swimming. A swim bladder is similar to a lung in structure and function in some primitive fishes, but it is not a lung because most cases its primary role is not respiration. Continue reading What are Swim Bladders?
The origin of new species from the existing one is called Speciation. It occurs when a group within a species migrates to a new area with different environmental conditions and develops its own unique features. Speciation has taken place over the course of evolution and may have played an important role in driving biodiversity on planet Earth. Continue reading What is Speciation?
Plant Tissue Culture is a technique of growing cells, tissues or organs in sterilized nutrient media under controlled aseptic conditions. The plant material to be cultured may be cells, tissues or plant organs such as excised root tip, shoot tip, shoot bud, leaf petiole, inflorescence, anther, embryo, ovule or ovary. Continue reading What is Plant Tissue Culture?
Cellular Totipotency is the ability of a single cell to produce all cell types and to organize them into an entire organism when cultured in a suitable culture medium at an appropriate temperature and aeration conditions. Spores and Zygote are examples of totipotent cells. Continue reading What is meant by Cellular Totipotency?
Explants are small pieces of plant parts or tissues that are aseptically cut and used to initiate a culture in a nutrient medium. Explants can be taken from different parts of a plant such as shoots, leaves, stems, flowers, roots, and from many types of mature cells provided they are able to de-differentiate into totipotent cells. Continue reading What are Explants?
The concept that the cell is the basic unit of life is known as Cell Theory. It is one of the most fundamental generalizations of biology and ranks with Charles Darwin’s theory of organic evolution and T.H. Morgan’s theory of the gene of modern biology. Continue reading What is Cell Theory?