Mendel and his Peas

The passing of traits from parents to offspring.

Gregor Mendel• Born 1822 in Austria• At 21 became a monk• Went to school in Vienna• Conducted his own scientific investigations

in the monastery garden.

Mendel’s Experiments

• Kept them simple and “controlled”

• Kept very good records

• Worked with pea plants

Mendel’s Experiments continued…

• He observed characteristics including seed shape, plant height and flower color.

• Only observed one characteristic at a time.

• A characteristic is a feature that has different forms in a population.

• Traits are the different forms that a characteristic can take.

Mendel’s First Experiment

• Created true-breeding plants before he started his experiments (He did this by breeding the plants for many generations until he always got the expected results.)

• When one true-breeding plant self pollinates all of the offspring will have the same traits as the parent.

Mendel’s First Experiment continued…

• He crossed (cross pollinated) true-breeding purple flowers with true-breeding white plants.

• He removed the anthers of one plant to make sure that they cross pollinated.

All of the offspring were purple

Mendel’s First Experiment continued…

• The purple flower was always present while the white flower seemed to disappear.

• He said the purple flowers was a dominant trait and the white flower was a recessive trait.

The same was true for the pea pod experiments.

Mendel’s Second Experiments

• He allowed the first generation plants (offspring of the first experiment) to self pollinate.

• The recessive trait reappeared in the second generation.

• He noticed a 3:1 ratio of the dominant to recessive traits.

• This ratio showed the relationship between two different things (traits)

Mendel realized…

• His results could only be explained if each plant had two sets of instructions for each characteristic.

• Each parent would donate one set of instructions but only one would show up in the offspring.

Use a Punnett Square to calculate the probability that offspring with a certain

characteristic will result.

First Generation (two true breeding parents)

Second Generation (both parents are not true breeding)