Biology | Heredity and Variation

Heredity and Variation

All members of a species have many characteristics in common, but no two individuals are exactly alike. The common characteristics are due to common heredity. These are transferred from parents to progeny via gametes. The differences are called variations and are caused by heritable mutations, i.e. sudden changed in the genetic material, change in the number of arrangement of genes on the chromosomes, and rearrangement of chromosomes of maternal and paternal origin in the zygote. Certain variations are established for a number of generations, it leads to a new characteristic, sometimes leading to the formation of a new species. In organisms reproducing asexually, a part of the parent body (bud, rhizome etc) separates and develops into new individual resembling parent without any variation.

In 1866, Gregor Johann Mendel reported the results of eight years of experiment and thought. These results were rediscovered after 34 years. Mendel formulated laws of inheritance based upon his experimental results. Later work by Sutton and Morgan suggested that the behaviour of chromosomes at mitosis and meiosis and their transmission to next generation follows a pattern similar to that postulated by Mendel for his characteristics controlling factors. They therefore hypothesized that chromosomes bar these factors (now called genes) or that the chromosomes are the physical basis of heredity. Each chromosome contains thousand of genes.

Genes reproduce themselves in exactly the same form, with only an occasional change – the mutation. Gene is made up of a chemical called DNA (Deoxyribo Nucleic Acid), which is the hereditary material, or the chemical basis of heredity.


Frictional Electricity | Physics Tutorial

Frictional Electricity

The word electricity is derived from the Greek word electron which means amber. In the sixth century BC, a Greek philosopher Thales found that when a piece of amber (a kind of resin) is rubbed with fur, it acquires a remarkable property; it attracts small pieces of leaves, cork or dust.

Today, we know that many other materials, such as hard rubber, nylon, plastic, sealing wax, etc. show the same effect. A substance which exhibits this effect is said to be electrified or charged.

You can see this kind of experiment by doing a simple experiment. On a dry day, place a few tiny pieces of paper on a table. Take a plastic ruler or comb and rub it with dry hair or a piece of wool and bring it near the pieces of paper. You will observe that the pieces of paper are attracted towards the rubber ruler or comb.

You may have experienced this attraction while combing your hair when dry or taking off a shirt made of synthetic fibre on a dry day. In each case, the object is charged by the rubbing process (i.e. by friction) and it is said to possess frictional or static electricity.

No significant advance was made in the understanding of the science of electricity until about AD 1600 when William Gilbert (1540-1603), a court physician to Queen Elizabeth I of England, undertook a detailed study of the kinds of material that would behave like amber. In his book De Magnate published in 1600, he gave the name electrica to substances like amber which when rubbed with suitable materials attracted tiny objects.