Main principles of Heredity and Mendel’s experiments

Main principles of Heredity

When you notice some traits in your family tree (grandfathers, parents, brothers, and sisters) you will find that there are two kinds of traits which are the hereditary traits and the acquired traits, The Hereditary traits are the traits that are transmitted from one generation to another.

The hereditary traits such as the hair colour, the skin colour, number of fingers and the blood groups, The acquired traits are the traits that are not transmitted from one generation to another such as the skill of playing football or writing.

How are the hereditary traits transmitted from one generation to another?

They are transferred from one generation to another generation through the reproduction process and they are governed by basics and laws, The science which studies these laws is called Genetics.

Genetics is the science that researches the transmission of the hereditary traits from one generation to another by studying the differences and the similarities between the parents and the offspring.



In the asexual reproduction, the similarity is exact because the children are produced from one parent cell, In the sexual reproduction, there are similarities and differences between the children as it is resulted from the coupling of two individuals.

Mendel’s experiments

The scientist Gregor Mendel was the first founder of heredity, Gregor Mendel was a monk, born in 1822 in Brunn, Austria, He performed his experiments using the pea plant in the garden of the monastery at Brunn.

Mendel carried out a group of experiments that explained how the hereditary traits are transmitted from one generation to another, And why some traits of the parents appear in their offspring.

Mendel performed his experiments using the pea plant because it is easy to be planted and it grows fast, Its life cycle is short, Its flowers are hermaphrodite, So, the pea plant can be self-pollinated, The pea plant can be easily artificially pollinated (the human intervention), The pea plant produces large number of plants in a generation, And it has several pairs of easily recognized contrasting traits.

Despite the numerous traits of pea plant, Mendel chose seven main traits to conduct his experiments such as the seed shape (smooth or wrinkled), The seed colour (yellow or green), The pod (fruit) colour (green or yellow), The pod (fruit) shape (swollen or sinuous), The flower colour (red or white), The flower position (side or end), the stem height (tall or short).

The inheritance of one pair of contrasting traits 

Mendel studied the inheritance of each pair of these contrasting traits separated by the following specific scientific steps, Mendel’s experiment studied the inheritance of the seed colour trait of the pea plant.

Mendel chose a pea plant that produces yellow seeds and other that produces green seeds for several generations, and he made self-pollination for these plants for several generations to be sure of the purity of this trait.

Mendel planted the seeds of these plants when the flowers appeared on the produced plants, he removed the stamens from these flowers before the anther become mature to ensure that the plant does not self-pollinate.

Mendel made cross-pollination for the flowers of yellow seed plants with the pollen grains from green seed plants, and for the flowers of green seed plants with the pollen grains from yellow seed plants.

Mendel covered the stigmas of the pistils in order not to cross-pollinate from other flowers then he planted the produced seeds, He observed that all the produced plants (first generation) have yellow seeds and the green coloured seeds trait disappeared completely.

Mendel let the first generation plants do self-pollination then he planted the resulting seeds, so he observed that the quarter of the produced plants (the second generation) is green seeds and three quarters are of yellow seeds.

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