CBSE Class 10 Answered

Mendels laboratory was a small garden in his monastery and his experimental material was a pure variety of garden pea plant called Pisum sativum. Mendel performed the first series of experiments with a single pair of contrasting characters or allele of a single trait such as height or colour or shape. He selected two varieties of pure plants, one with a tall stem and the other with a dwarf stem. He then crossed these two plants taking care to prevent self pollination by emasculation. He also prevented coss fertilisation by other pollen grains.

When the seeds were obtained and sown, he found that the offsprings developed were all tall like one of the parents. These offsprings obtained by crossing two pure plants with contrasting characters are called hybrids and their generation is designated as F1 generation. Mendel then allowed the hybrid talls of F1 generation to self fertilise. When their seeds were collected and sown, they gave rise to both the tall and dwarf offsprings, like original parents. However, the ratio of tall to dwarf plants was approximately 3:1. This generation resulting by selfing of FI hybrids was named as F2 generation.

For dihybrid experiment, Mendel crossed a pure pea plant having yellow round seeds with another pure pea plant having green wrinkled seeds. The FI hybrids were all yellow round indicating that these are dominant characters. When the hybrids were selfed, they gave four types of offsprings in F2 which were yellow round, yellow wrinkled, green round and green wrinkled. They were in ratio of 9:3:3:1. From the results of his experiments, Mendel was convinced that the transmission of characters follows some definite pattern and accordingly he proposed some laws, popularly known as Laws of Inheritance or Mendel's laws.