Gregor Mendel Discovers The Principles of Inheritance

Lone Peak High School

Biology 2002-03

By Brad Shuler

Who was Gregor Mendel?

Born in 1822

Studied science, mathematics and statistics

Entered an Austrian monastery to be a monk

Studied heredity in peas

Discovered the principles of heredity

Mendel’s Observations

He identified that pea plants have a variety of traits when observing the different characteristics of the plant.

He developed “pure” strains of plants. (i.e. tall, short, green pod, yellow pod, wrinkled, round, etc.) These are often called purebreds.

The purebred plants consistently produced offspring with the given trait. (i.e. tall always produced tall)

Mendel’s PeasThese are the seven characteristics, each having two contrasting traits, that Mendel identified.

Mendel’s Experiments He experimentally

crosses different strains of “pure” plants (parental generation) to develop hybrids (F1 generation).

He then crossed these hybrids (F1 gen.) and analyzed the results (F2 gen.)

Mendel’s Results The hybrids (F1 gen.) only displayed one of the parental

traits. (tall) When crossing two hybrids, some of the resulting

offspring (F2 gen.) displayed one of the parental traits and some displayed the other. (some tall some short)

These traits in the F2 generation consistently occurred in a 3 to 1 ratio. (3 tall: 1short)

Mendel’s Conlusions:The Principle of Segregation

Each plant has two “factors” (genes) for any given characteristic (length of stem, color of pod, shape of seed, etc.)

They receive these “factors” from their parents.

When a plant reproduces it only passes one of its two “factors” to its offspring. The “factors” are contained in the gametes, the egg or sperm.

Mendel’s Conlusions:The Principle of Dominance and Recessiveness

Factors for certain traits seem to mask or hide the others when both are present in hybrids (Tt=tall).

Factors that are that always displayed when present are called “dominant”.

Factors that are hidden or masked by the dominant are called “recessive”.

Recessive traits are only displayed in purebreds (i.e. short-tt, yellow pod-yy).

The End