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Admin Product | January 4th, 2021
CBSE Class 12th Laws of Inheritance

"Inheritance" means acquiring character traits by an offspring from its Parent. According to Mendel's Laws of Inheritance, this process takes place in sexually-reproducing organisms. He conducted Hybridisation of the pea-plant to observe how inheritance occurs in a garden pea plant.

Major Conclusions of Mendel's Experiment:

1. Statistical analysis done on a large quantity (14 varieties of garden pea-plants) of sample provided basic framework of inheritance process.

2. The authenticity of the theory could be proved due to logical and mathematical deduction of data.

3. Consecutive self-pollination of true breed of pea-plant proved that stable self-inheritance is possible.

How was the experiment conducted?

#Step 1: A tall pea- plant and a short pea plant were cross-pollinated. [In cross-pollination, male and female flower are present on different plant.] The seeds resulting from this were collected. These seeds were then grown. It was observed that all plants were tall. These plants were termed as First Filial Genreation/ F1 Generation.

#Step 2: The F1 plants were self-pollinated. [In self-pollination, male and female flower belong to same plant.] The seeds resulting from this were collected. These seeds were then grown. It was observed that some plants were tall some were short in height. No plant had mid-height. The ratio of tall plants to short plants was 3:1.

Terminology Used:

Filial Generation/ F1 Generation, Factors/ Genes, Alleles, Homozygous, Heterozygous, Genotype, Phenotype

1. Factors or Genes was something which was stably passed from one generation to other acting as a unit of inheritance.

Factors or Genes carry information for a particular characteristic.

2. If the Factor of height was taken into account, the factor for tall height represented as T and the factor for short height represented as t are Alleles.

Hence, Alleles are genes carrying information opposite to each other but related to same characteristic. For example, T and t carry information related to same characteristic of height but one is for Tall-height and the other is for Short-height respectively; hence Tt are alleles.

3. According to Mendel, a Homozygous plant is a true breed and has identical alleles, like, tt or TT. A Heterozygous plant has contrasting alleles, like, Tt.

4. The representation of genetic factors in words is termed as Phenotype (Tall, Dwarf). The representation of genetic factors in alphabetical symbols is termed as Genotype (T, t).

Law of Dominance:

When the plants showed no mixing of traits but a dominance of a single trait, it was inferred that genes occur in pairs. During the process of meiosis the pair gets separated and genes intermix. After this, the resulting trait which the offspring expresses becomes the Dominant Trait. Step 1 of the experiment had parents with both tall and short height but offspring were tall-height, so in case of the garden pea plant, the dominant trait is tall-height of the plant.

Law of Segregation:

During formation of the Zygote the parent genes mix. The parent may be heterozygous but due to segregation or separation of chromosomes during the process of meiosis, there is no blending of the characters.

These two laws, however, are based on the theory that only single gene is inherited. When scientists further studied inheritance, the process showed co-dominance, incomplete dominance, etc.

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