Gregor Mendel, an Austrian monk, is known as the “father of genetics.” Through his experiments with garden pea plants, he discovered important principles about how traits are passed from parents to offspring. Genetics is the scientific study of heredity, which is the passing of characteristics from one generation to the next. These characteristics are called traits.

Mendel chose pea plants for his experiments because they grow quickly and have easily observable traits, such as height, seed shape, and color. He understood that pea plants produce male and female sex cells, called gametes, and that fertilization occurs when these cells join to form a zygote. This zygote develops into a seed that will grow into a new plant.

To ensure accurate results, Mendel used true-breeding plants—plants that, when allowed to self-pollinate, always produce offspring identical to themselves. These plants made up the parent generation, or P generation. The offspring of this generation are called the first filial generation (F1), and the offspring of the F1 generation are called the second filial generation (F2).

Mendel carefully controlled pollination using a method called cross-pollination. He removed the stamens (male parts) from a flower to prevent self-pollination and then transferred pollen from another plant to the pistil (female part). This allowed him to control which plants reproduced and to track how traits were passed on.

In his experiments, Mendel studied one trait at a time. For example, he crossed a true-breeding tall pea plant with a true-breeding short pea plant to observe how height was inherited. Offspring produced by parents with different forms of a trait are called hybrids. When only one trait is studied, the cross is called a monohybrid cross.

This diagram below shows how stem height is passed from one generation to the next in pea plants.

P Generation (Parent Generation):
At the top, a tall plant is crossed with a short plant. These are true-breeding plants, meaning their traits are pure (TT for tall and tt for short).

F1 Generation (First Generation):
All the offspring are tall. Even though they received one gene for shortness, the tall trait is dominant, so it hides (masks) the short trait. These plants are hybrids (Tt).

F2 Generation (Second Generation):
When two hybrid tall plants (Tt × Tt) are crossed, the offspring show a pattern:

• 3 plants are tall
• 1 plant is short

This creates a 3:1 ratio of tall to short plants.

What This Shows:

• The short trait never disappeared—it was just hidden in the F1 generation.
• Traits are controlled by pairs of genes (alleles).
• Dominant traits (tall) can mask recessive traits (short).
• Recessive traits only appear when an organism has two recessive alleles (tt).

Review:

1. What is heredity?
2. What is a true-breeding plant?
3. Explain cross-pollination.