D3.2.2 Methods for conducting genetic crosses in flowering plants Notes

Conducting Genetic Crosses in Flowering Plants Reveals Patterns of Inheritance

1. Understanding how traits are inherited involves carefully planned genetic crosses.
2. In flowering plants, this process uses controlled pollination to track how traits pass from one generation to the next.

Pollination Transfers Male Gametes to Female Gametes

1. Male gametes are found in pollen grains produced by the anthers.
2. Female gametes are located in ovules within the ovary.

Types of Pollination

1. Self-Pollination: Pollen from the anther fertilizes ovules on the same plant. This results in self-fertilization and produces genetically similar offspring.
2. Cross-Pollination: Pollen from one plant fertilizes ovules of another plant, promoting genetic diversity.

Steps for Conducting Genetic Crosses

1. Select Parent Plants: Choose two plants with contrasting traits (e.g., tall vs. dwarf plants).
2. Prevent Unwanted Pollination:
   1. Remove anthers from the female parent’s flower to stop self-pollination.
   2. Enclose the flower in a paper bag to prevent external pollen from contaminating the cross.
3. Transfer Pollen: Use a small brush to transfer pollen from the anther of the male parent to the stigma of the female parent.
4. Track Fertilization and Seed Development:
   1. Pollen germinates, and a pollen tube grows down the style to deliver male gametes to the ovary.
   2. Fertilized ovules develop into seeds, which contain the next generation.

Generations in Genetic Crosses: P, F1, and F2

1. P Generation (Parental Generation): The original plants used in the cross.
2. F1 Generation (First Filial Generation): The offspring of the P generation.
3. F2 Generation (Second Filial Generation): Produced by self-pollinating or cross-pollinating F1 plants.

Predict Offspring Traits with Punnett Grids

How to Use a Punnett Grid

1. Identify Parent Genotypes: Determine the alleles carried by each parent.
2. List Gametes: Write the possible gametes along the grid's top and side.
3. Combine Gametes: Fill in the grid to show possible offspring genotypes.
4. Interpret Results: Use the grid to predict phenotypes and calculate trait ratios.