Question

Describe how Mendel cross-fertilized and self-fertilized pea plants.

Answer 1

Answer: Fertilisation is union of male gamate with the female gamate.

Self fertilisation takes place when the male gamate of the flower unites with the female gamate of the same flower, the progenies obtained from self fertilisation are similar to the parents.

Cross fertilisation is when the male gamate of one flower unites with the female gamate of another flower of the same species as was done in Mendel’s experiment to produce hybrid progenies.

Mendel chose garden pea plant (Pisum sativum) for the study of inheritance. Pea plant is easy to grow and handle. It produces many seeds, since it is an annual plant 3-4 generations can be obtained in a year. Besides all these there was one advantage of pea plants i.e. they are self fertilising, Mendel did not have to do anything to self fertilise the pea plants. Mendel studied the seven characters in the pea plant and kept their records for the statistical analysis.

The pea plant is naturally self fertilised as it is a bisexual flower with male reproductive part (anthers) and female reproductive part (carpel) present in the same flower. For the fertilisation to occur there has to be fusion of male gamate (pollen) and the female gamate which is present in the ovary.

To ensure self fertilisation in the pea plant naturally, the petals of the plant cover the flower till pollination (transfer of pollen to the female gamate) is complete within the flower. Hence pea plants are naturally self fertilising

Cross fertilisation is performed to produce hybrids. In cross fertilisation both the gamates are taken from two different varieties, or gamates are taken from pea plants showing different set of characters.

Cross fertilisation experiments performed by Mendel: To perform cross fertilisation, when the pea plant is in the bud condition it’s anthers are removed this process is known as emasculation. Removal of anthers before the formation of male gamate is to ensure that there is no self fertilisation. Once the anthers are removed, this particular pea plant will serve as the female plant. Then the pollens from another pea plant are removed and are dusted on the stigma of this emasculated pea flower. The emasculated flowers were covered with a paper bag to prevent pollination with any other pollen than the desired one. And they were properly tagged. This way cross fertilisation experiments were carried out by Mendel.