MENDEL & HIS PEAS Chapter 5 Section 1

OBJECTIVES:

Explain the relationship between traits and heredity

Describe the experiments of Gregor Mendel

Explain the difference between dominant and recessive traits

HEREDITY:

Passing of traits from parents to offspring

About 150 years ago Gregor Mendel performed experiments to study traits

WHO WAS GREGOR MENDEL?

Born in 1822 in Austria

Learned a lot about flowers and fruit trees

Entered a monastery at 21 and learned how to conduct scientific experiments

Mendel had trouble in school, but continued his research on principles of heredity in the monastery gardens

UNRAVELING THE MYSTERY:

Mendel noticed patterns of inheritance

He wanted to learn what caused the patterns he witnessed

He decided to study garden pea plants, to keep it simple

SELF-POLLINATING PEAS

A good choice – pea plants grow quickly; there are many different kinds; they can also self-pollinate

Mendel was therefore able to grow a true-breeding plant (all offspring will have the same traits as the parent)

Pea plants can also cross-pollinate (one plant fertilizes the ovule of a flower in a different plant) – pollen is carried by insect or wind

CHARACTERISTICS:

Mendel studied one characteristic (feature) at a time

Example characteristic: hair color in humans; traits (forms) could be brown or red hair

Characteristics in plants: Flower color (traits: purple or white) Seed shape (traits: round or wrinkled) Plant height (traits: tall or short)

MIX & MATCH:

Mendel was careful to use plants that were true-breeding for each of the traits he was studying

What would happen if he bred or crossed 2 plants with different traits of a single characteristic?

He removed the anthers (male parts) so that they could not self-pollinate

He used pollen from another plant to fertilze

CROSS POLLINATION OF THE PEA PLANT:

http://mac122.icu.ac.jp/gen-ed/mendel-gifs/02a-pea-cross-fert.JPG

MENDEL’S 1ST EXPERIMENTS:

Crossed pea plants to study 7 different characteristics

First-generation plants: the offspring from the 1st cross

Experiment: 2 plants with purple or white flowers were

crossed First-generation plants were all purple The white flower trait seemed to disappear

MENDEL’S 2ND EXPERIMENTS:

The mature flowers were allowed to self-pollinate

The white flowers reappeared in the second-generation

The trait that appeared (purple flowers): dominant trait

The trait that disappeared or faded (white flowers): recessive trait

MENDEL’S 2ND EXPERIMENTS:

For every 3 plants with purple flowers, there was 1 plant with white flowers

RATIOS IN MENDEL’S EXPERIMENTS:

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

Mendel decided to calculate the ratio of dominant-to-recessive for each characteristic

Turn to page 118, Table 1 in your textbook…

Results: 705 purple to 224 white (3.15:1) or 3:1

CALCULATE THE RATIOS IN THE REST OF THE TABLE:

GREGOR MENDEL – GONE BUT NOT FORGOTTEN…

In 1865 Mendel published his findings

It wasn’t until 20 years later that his ideas were recognized and accepted

This opened the door to modern day genetics

QUICK QUIZ:

What did Mendel call the trait that appeared in all of his first-generation plants?

What is the probability of getting heads in a coin toss?

REFERENCE:

Holt Science and Technology: Life Science. Austin: Holt Rinehart & Winston, 2007. Print.