Gregor Mendel's Principles

The Beginning of Genetics

All scientific breakthroughs, like the discovery of the structure of genes and how they function, could not have just happened. Just like any great discovery it must have had an origin, a beginning.

Genetics as we know it today began in a monastery in Austria in the 1860s. A monk named Gregor Mendel (1822-1884) was curious as to how animal and plant traits were inherited, so he began to study garden peas. He studied the peas for eight years and in this time he built the founding principles of heredity and ultimately what would be called genetics.

Mendel's Experiment Mendel used a technique called cross-pollination to have pea offspring that inherited its traits from two different parents. He only paid attention to one trait at a time as he studied the patterns of inheritance. He also used many plants in order to lessen the influence of chance in his experiments. Mendel throughout his study, worked with seven distinct traits. In the first experiments he observed seed shape (round vs. wrinkled).

The First Cross

In the first experiments, Mendel crossed pure-breeding plants that produced smooth seeds with those that produced wrinkled seeds. The outcome was seeds that were round. There were no more wrinkled seeds. Today the parent generation is symbolized by P and the next generation is symbolized by F1. Mendel let the offspring grow into plants and self-pollinate. This gave rise to the F2 generation.

The F2 generation produced a cool effect. Three quarters of the seeds produced were round, and one-quarter was wrinkled. Mendel coined the term 'dominant' for

the round side of the trait, and 'recessive' for the wrinkled.

Mendel would go on to repeat the two-generation cross for the six other traits. The F2 generation would always produce traits that had the dominant to recessive ratio at 3:1. These results led Mendel to hypothesize that each pure-breeding plant had two identical copies of a unit or factor of a specific trait (we now call these alleles!). He didn't know how they were structured or where they were located but he went on to hypothesize that only one copy of the units went into each gamete (sperm or egg) created.

How do scientific breakthroughs happen?

Describe Mendel’s experiment.

What was the difference between F1 and F2?

Directions: Answer the questions in the boxes and fill out the back of the sheet.

Question: Why is Gregor Mendel important?

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