Notes from NEET topper
Self pollination in F1 plants
In Mendel’s experiments with pea plants, self-pollination of F1 plants produced predictable results due to the principles of inheritance he discovered.
1. F1 Generation (First Filial Generation): Mendel’s F1 generation resulted from the cross of two purebred, homozygous parental plants that differed in a specific trait. For example, he crossed purebred purple-flowered (PP) and purebred white-flowered (pp) pea plants. The F1 generation, as a result, consisted of all heterozygous purple-flowered (Pp) plants.
2. Genetic Makeup of F1 Plants: All F1 plants are heterozygous (Pp) for the trait under consideration. In this case, they have one dominant allele (P) and one recessive allele (p) for flower color.
3. Phenotype of F1 Plants: The phenotypic appearance of all F1 plants is the dominant trait, which is purple flowers. This is because the dominant allele (P) masks the expression of the recessive allele (p).
4. Self-Pollination of F1 Plants: When Mendel allowed the F1 plants to self-pollinate, he essentially allowed them to produce gametes (sperm and eggs) and fertilize themselves. Each F1 plant can produce two types of gametes: one carrying the dominant allele (P) and the other carrying the recessive allele (p).
5. Fertilization in F1 Self-Pollination: During self-pollination, each F1 plant can randomly combine its gametes. This means that each plant can produce offspring with two possible combinations of alleles: PP or Pp. Remember that PP represents the homozygous dominant genotype (purple flowers), while Pp represents the heterozygous genotype (purple flowers).
6. F2 Generation (Second Filial Generation): The offspring resulting from self-pollination of the F1 generation make up the F2 generation. In Mendel’s experiments, he observed that approximately 75% of the F2 plants had purple flowers (PP or Pp), and about 25% had white flowers (pp).
7. Phenotypic Ratio in F2: The phenotypic ratio in the F2 generation is approximately 3:1, with 75% exhibiting the dominant trait (purple flowers) and 25% exhibiting the recessive trait (white flowers).
