TNPSC - 10th Standard Science Notes for All Competitive Exams

Heredity and Evolution


The Progeny produced through the reproductive process is similar to its parents, in body design, functions etc. The rules of heredity determine the process by which the traits and the characteristics are relatively inherited.

Gregor Johann Mendel (1822-1884)
Mendel was educated in a monastery and went on to study  science and Mathematics at the University of Vienna. Gregor Johann Mendel worked out the first ever scientific experimental study of heredity. Mendel as Austrian Augustinian monk observed variation in the characteristics of garden pea plant (Pisum Sativum) which he had cultivated in his monastery garden. The visible contrasting characters that Mendel observed in the garden pea plant were
  • Seed shape - Round / Wrinkled
  • Seed colour - Ywllow / Green
  • Flower Colour - Violet / White
  • Pod Shape - Full / Constricted
  • Flower Position - Axillary / Terminal
  • Stem height - Tall / Dwarf
Mendel's Monohybrid Cross
Mendel selected the garden pea plant, pisum sativum for his experiments.  He selected tall and dwarf plants and allowed them to grow naturally. As pea plants produce seeds only by self pollination, he observed that tall plants produced always tall plants generation  after generation under natural condition.

Monobybrid Crass.
The first experiment of Mendel considering the inheritance of a single trait (Height of the plant Tall / Dwarf) is called Monobybrid Crass.

Express of Morphological characters as tall or dwarf plan, violet or white flower is called phenotype.

The expression of gene (or Chromosomal make up) of an individual for a particular trait is called Genotype.

Types of Variations
a Somatic Variation
It pertains to body cells and it is not inherited
b. Germinal Variation
It pertains to germ cells or gametes and it is inheritable. It leads to speciation and evolution.

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