Gregor Mendel

It is clear that Mendel's success where others had failed was not just the result of good luck. The introduction to his published report shows that he was familiar with the work of other scientists and recognized what mistakes they had made:

"Whoever surveys the work in this field will come to the conviction that among the numerous experiments not one has been carried out to an extent or in a manner that would make it possible to determine the number of different forms in which hybrid offspring appear, permit classification of these forms in each generation with certainty, and ascertain their numerical relationships."

Mendel correcty recognized that the experiment needed to answer two essential questions: How many different kinds of offspring result? and How many are produced of each kind? He also recognized that the choice of the plant group for the experiments was an important one. He wrote:

1. The experimental plants must necessarily possess constant differing traits.
2. The hybrids must be protected from the influence of all foreign pollen during the flowering period or easily lend themselves to such protection.
3. There should be no marked disturbance in the fertility of the hybrids and their offspring in successive generations.

Mendel knew that peas had a flower structure that inhibited cross-pollination. The reproductive parts of the pea flower are completely enclosed by the petals. Before the flower even opens, the anthers (male organs) burst and dust pollen all over the stigma (female organ). Thus unless an insect (or a scientist) interferes, self-pollination is virtually certain.

Pea flowers are always either purple or white; there is no blending of these traits, which are clearly hereditary. A given plant produces only purple flowers or only white flowers. (It happens that this trait can be recognized in the seed before it is even planted. If the semitransparent seed coat is gray, the plant it produces will have only purple flowers. If the seed coat is white, only white flowers will be produced.) Mendel chose the other traits for his experiments to have the same sharp differences. On any given plant, all the flowers are axial (growing out of the axil, the junction where a leaf grows from the side of a stem) or terminal (growing out of the end of a stem). In height, pea plants are always either tall (over 2 meters) or dwarf (less than 1 meter). Medium-tall or semi-dwarf pea plants never occur. Seeds are either green or yellow and either smooth or angular. The pods in which the seeds grow are either green or yellow and either inflated or deflated. Each of these traits is distinct from its opposite, and there is never an in-between state.

After reading the above information about Mendel and his peas, circle the LETTER of the best answer for each of the following questions:

Mendel's Peas Reading Assignment       Name ______________________

1. What do many great scientists emphasize as the most important step in a scientific investigation?
    
   1. Perform an organized experiment.
   2. Form a clear hypothesis.
   3. Make a clear statement of the experimental question.
   
    
2. What two essential questions were answered in Mendel's experiment?
    
   1. Will all offspring look alike? & Why do they look different?
   2. How many kinds of offspring are produced? & How many of each kind?
   3. How many chromosomes are in plant? & Are the chromosomes different?
   
    
3. Why did Mendel only use seven pairs of traits in his experiment?
    
   1. Pea plants only have seven traits.
   2. These traits were always one or the other, never "more or less".
   3. His plants were bothered by insects.
   
    
4. Why does the structure of pea flowers inhibit cross-pollination?
    
   1. Some pea flowers don't have reproductive structures.
   2. The reproductive parts are enclosed by the petals.
   3. Different plants have different sex flowers
   
    
5. Which of these are male flower organs?
    
   1. Stigmas
   2. Sepals
   3. Anthers
   
    
6. Which of these are female flower organs?
    
   1. Stigmas
   2. Sepals
   3. Anthers
   
    

    
   

7. Pea flowers are always one of two colors. What are they?
    
   1. Pink and White
   2. Yellow and Purple
   3. Purple and White
   
    
8. What characteristic of a pea seed can be used to determine what color of flowers the plant will produce?
    
   1. seed shape
   2. seed size
   3. seed color
   
    
9. What is a flower called that grows from the side of a plant stem?
    
   1. axial
   2. terminal
   3. lateral
   
    
10. How tall is a "tall" pea plant?
     
    1. less than 1 meter
    2. over 2 meters
    3. neither of these