A true breeding line is one that, having undergone continuous self pollination, shows the stable trait inheritance and expression for several generations,

Answer

### Step-by-Step Solution:

1. **Definition of True Breeding Line**: A true breeding line refers to a group of organisms that, when self-pollinated, consistently produce offspring that exhibit the same traits over multiple generations.

2. **Self-Pollination**: This process involves the transfer of pollen from the male part of a flower to the female part of the same flower, allowing for fertilization without the introduction of genetic material from another plant.

3. **Stable Trait Inheritance**: In a true breeding line, the traits expressed in the offspring remain stable and unchanged across generations. This stability is due to the genetic makeup of the organisms involved.

4. **Genotype Consideration**: True breeding organisms are typically homozygous for the traits in question. This means they possess two identical alleles for a particular gene, either both dominant (homozygous dominant) or both recessive (homozygous recessive).

5. **Lack of Variation**: Because true breeding lines are homozygous, there is a reduced chance of variation in traits. When self-pollinating, the offspring will inherit the same alleles from their parents, leading to consistent expression of traits.

6. **Generational Consistency**: Over several generations of self-pollination, the traits remain unchanged, confirming the stability of the true breeding line.