Tamil Nadu Board of Secondary EducationHSC Science Class 12

Mendel’s experiments on pea plant

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Notes

Mendel's experiments on pea plant:

  • For seven years (1856-1863), Gregor Mendel conducted hybridization experiments on garden peas and postulated the rules of heredity in living beings. 
  • His experiments on pea plants were based on two opposing traits e.g. tall and dwarf for height, yellow and green for seed color, and round or wrinkled for the seed shape.
  • He choose characters with two opposing characteristics and completed his hybridization experiments on 14 true-breeding pea plant varieties.
  • Mendel’s theory of inheritance, known as the Particulate theory, establishes the existence of minute particles or hereditary units or factors, which are now called as genes.
  • He performed artificial pollination or cross-pollination experiments with several true-breeding lines of pea plants.
  • True breeding lines (Pure-breeding strains) mean it has undergone continuous self-pollination having stable trait inheritance from parent to offspring. Matings within pure breeding lines produce offspring having specific parental traits that are constant in inheritance and expression for many generations.
  • Pure line breed refers to homozygosity only. Fusion of male and female gametes produced by the same individual i.e pollen and egg are derived from the same plant is known as self-fertilization.
  • Self-pollination takes place in Mendel’s peas. The experimenter can remove the anthers (Emasculation) before fertilization and transfer the pollen from another variety of pea to the stigma of flowers where the anthers are removed. This results in cross-fertilization, which leads to the creation of hybrid varieties with different traits.
  • Mendel’s work on the study of the pattern of inheritance and the principles or laws formulated, now constitute Mendelian Genetics.

The seven pairs of contrasting characters studied by Mendel in pea plant:



Seven characters of Pisum sativum studied by Mendel

Mendel’s seven characters in Garden Peas, shown on the plant’s seven chromosomes

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Genetic mystery of Mendel’s white flowers:

Purple flower of Pea with Pea Gene A and White flower of Pea

It is quite fascinating to trace Mendel’s genes. In 2010, the gene responsible for regulating flower colour in peas were identified by an international team of researchers. It was called Pea Gene A which encodes a protein that functions as a transcription factor which is responsible for the production of anthocyanin pigment. So the flowers are purple. Pea plants with white flowers do not have anthocyanin, even though they have the gene that encodes the enzyme involved in anthocyanin synthesis.

Researchers delivered normal copies of gene A into the cells of the petals of white flowers by the gene gun method. When Gene A entered in a small percentage of cells of white flowers it is expressed in those particular cells, accumulated anthocyanin pigments, and became purple. In white flowers, the gene A sequence showed a single-nucleotide change that makes the transcription factor inactive. So the mutant form of gene A do not accumulate anthocyanin and hence they are white.

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