Mendel and His Peas

Gregor Mendel discovered the principles of heredity while studying pea plants.

Gregor Mendel

Austrian scientist who discovered basic ideas of heredity while working with the pea plant

Self-Pollinating Peas

Pea plants grow quickly

Peas self-pollinate = has both male and female reproductive structures

Pollen from ONE flower can fertilize the ovule of the SAME flower and/or the ovule from another plant

Flower Power PEDUNCLE—stalk of the flower

RECEPTACLE—part of the stalk where the flower is attached

SEPAL—the outer parts of the flower that wrap up the growing bud

PETAL—the colored parts of the flower

STAMEN—pollen producing part of the flower

ANTHER—part of stamen where pollen is produced

PISTIL—ovule producing part of a flower; ovary often supports a long style, topped by a stigma; mature ovary is a fruit and the mature ovule is a seed

STIGMA—part of the pistil where pollen germinates

OVARY—enlarged basal portion of the pistil where ovules are produced

Self-Pollinating Plants

Why is it important that pea plants self-pollinate?

Eggs and sperm from the same plant combine to form a new plant which was actually a TRUE-BREEDING PLANT

True-Breeding Plants self-pollinate and create offspring that will have the same trait (ex—the color of the petals) as the parent

Self-Pollinating Plants

Pea plants also CROSS-POLLINATE

Cross-pollination = pollen from one plant fertilizes the ovule of a flower on a different plant

Pollen can be carried by insects (ex—a bee), the wind, birds, and other small creatures

Characteristics

Characteristic = a feature that has different forms in a population (ex—hair color in humans)

Mendel used plants that has different characteristics in order to figure out how he could change those characteristics in offspring (ex—flowers that were one color may produce offspring with a different color)

Mendel’s First Experiments

1st Experiment—studies 7 different characteristics

He used plants that were true-breeding for different traits for each characteristic (ex—crossed plants with purple flowers with plants that had white flowers)

FIRST-GENERATION PLANTS = the offspring from a cross [see above]

Mendel’s First Experiments

Similar results were discovered with each cross

DOMINANT TRAIT = the trait that is always present in the first generation

RECESSIVE TRAIT = the trait that always seemed to disappear in the first generation

Mendel’s Second Experiments

Mendel allowed the first-generation plants to self-pollinate

The recessive trait for white flowers reappeared in the 2nd generation!

After repeating the experiment on each of the 7 characteristics Mendel learned that in the 2nd generation the recessive trait reappeared in some of the plants

Ratios in Mendel’s Experiments

The recessive trait did not show up as often as the dominant trait

Ratio = a relationship between two different numbers that is often expressed as a fraction

Dominant-to-Recessive Ratio

Section Review

Please complete the entire Section Review on page 61 of your textbook!