Subject: Integrated Science
Topic: Heredity
Age: 10-15 years
Period: Single
Duration: 45 Minutes
Date: May 10, 2020
In our last class, we explained that heredity is the transmission of characteristics from parents to offsprings. Today, we are going to intensively explain the two types of heredity mentioned in our last class.
Dominant character or traits
This is the character that is expressed without the influence of a contrasting character or traits which appears in a family, from grandfather to father and to children. It is controlled by a dominant gene.
Recessive character or traits
This is a character, which does not produce its effect in the presence of the dominant character or traits which appears in the grandfather, disappears in the father and re-appears in the children. It is controlled by a recessive gene. A recessive gene will often not appear for one generation and reappear in another generation, e.g albinism.
Gregor Mendel demonstrated this phenomenon of dominant and recessive gene with an experiment using varieties of garden peas.
In one of his experiments, he removed the stamens from the red pea flowers, before the pollen grains were shed. This was to prevent self pollination.
He then placed the pollen from the white flowered pea on the stigma of the red flowered pea, that is, cross pollination.
He planted the seed resulting from the cross pollination. When the seeds grew, all the plants produced red flowers. These are the first generation cross breed or hybrid.
In the second generation plants, Mendel allowed self pollination to occur by preventing insects from reaching the flowers. When he planted the seeds resulting from self pollination, some of the pea plants produced red flowers and some produced white flowers.
From the experiment,the first generation peas bore only red flowers,even though they also received the gene for white flower from the other parent. It therefore followed that, the red color gene is dominant, while the white color gene is recessive.
Activity
See you in our next class.
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