Class 10 Science (biology) Heredity and Evolution

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~ HEREDITY 

The transmission of traits from parents to offsprings is termed as heredity. This transmission takes place by the process of reproduction. The reproductive process generates the individuals of similar design. The transmission or inheritance of characteristics from parents to offsprings is governed by certain well defined rules called the rules of heredity. 

INHERITED TRAITS  

The traits (characteristics) obtained from parents are termed as inherited traits. You must have seen a number of children similar to their parent (s). This is because of the traits which they inherited from their parents. Body design, shape, colour, etc. are all inherited from parents. Though all human beings are similar, still they possess variations. For example, free and attached earlobes are two variants found in human populations. 

Rules for the Inheritance of Traits : Mendel ' s Contributions

Every human individual has two copies of genetic material, i.e. DNA. The gametes produced by parents contain a single copy of this DNA. When the male and female gametes fuse, the zygote acquires two copies of DNA, one from mother and the other from father. Now since it is the DNA which determines the trait it can be concluded that each trait is influenced by both maternal as well as paternal DNA. In other words, there will be two versions of DNA for controlling a single trait. Now which trait will express itself (maternal or paternal) is a question which Gregor Johann Mendel tried to answer by his experiments. The results of his experiments. The results of his experiments are applicable to almost all the sexually reproducing organisms.  

Mendel ' s Experimental Plant 

Between 1856 and 1863, Mendal conducted his experiments on garden pea (possum sativum). He selected this plant for his experiments because of the following reasons : 

* The plant has a short life cycle. Thus results can be obtained in a short period of time. 

* The plant has some well defined easily detectable contrasting traits, e.g. some plants were long and some were short. 

* It is easier to raise, maintain and handle the plants. 

* Large number of seeds are produced in one generation. 

* Pea plants pure for each for each of the seven characters selected by Mendel were readily available.

* The reproductive organs are large enough to be seen with naked eye. This makes cross-pollination easier. 

Mendel conducted his experiments in monastery garden. For his experiments Mendel noted seven contrasting characters in plants which are us under : 


Before the process of experimentation, Mendel developed plants which were pure for their characters. e.g. he developed yellow seeds which produced plants with yellow seeds only. Similarly he obtained plants which were pure for other characters as well. 


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