Do you know what is heredity? We have heard of the word hereditary. What does this word mean? The word hereditary is derived from the word heredity. The word hereditary refers to some trait or characteristic or even an item that is inherited from our parents.
In the article on reproduction, we had learned that both the parents contribute an equal amount of genetic material to the offspring. Thus, for each trait, we inherit one copy from our mother and one from our father. So, which trait will be expressed in the offspring? Are there any rules that determine which character is expressed and to what extent?
These were some of the questions on heredity that were answered by Gregor Mendel, an Austrian scientist. Mendel is often hailed as the father of modern genetics. He performed many experiments to elucidate the nature of heredity. He took pea plants with many different characteristics like round/wrinkled seeds, tall/short plants, white/violet flowers, etc. He cross-bred these plants and noted the features of the offspring.
In the first generation offspring, he noted that there were no midway characteristics. For e.g. when a tall plant was bred with a short plant, the offspring was all tall. When this offspring was allowed to produce by self-pollination, Mendel noted that a quarter of the offspring was short while ? of the offspring were tall in character. Therefore, he inferred that that the 1st generation offspring or F1 had inherited the tall and short trait from its parents, but only the tall character was manifest in the 1st generation of offspring. He called the tall trait as dominant trait while the short characteristic was the recessive trait.
A question naturally arises- why were a quarter of plants in the 2nd generation short?
Mendel postulated that the 1st generation offspring would have inherited both traits (tall and short) from its parents. We shall call these traits T & t. So, the tall parent is TT, and the short parent is tt.
The first generation offspring is Tt. When this plant reproduces by self-pollination, then there are four possible combinations that can be produced- TT, Tt, Tt and tt. Therefore, ? of the 2nd generation of plants are short. The characteristic T & t are now referred to as genes.
Based on his experiments with peas, Mendel proposed a set of rules of heredity. Organisms that reproduce by these rules of heredity are said to follow Mendelian genetics. However, not all traits are inherited in accordance with Mendel?s laws. We will learn about non-Mendelian inheritance in another article.
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