SUBTOPIC: Mendelian Inheritance in the Mechanisms of Evolution

OBJECTIVES:

The students will:

1) understand the mechanism of Mendelian Inheritance

2) explain the frequent differences between the theoretical phenotypic ratio and the actual results from a breeding in which several offspring result

3) understand the importance of Mendelian Inheritance in the mechanism of evolution

Many people believed that Charles Darwin was the man who originated the idea of evolution. In fact, others before Darwin had discussed the idea of a descent of species. No one, however, was successful in providing a persuasive account of heredity. 

After Darwin's death Gregor Mendel attempted to study the mechanism of heredity through experimentation. He explained that inheritance was like beads on a string which combined in definite mathematical ratios. Mendel succeeded where others had failed to reach conclusions about the inheritance of traits. Mendel first experimented with the cross breeding of mice. He knew from his farm background that crossbreeding stock animals resulted in the appearance or disappearance of various traits, and he attempted to find any common ground that existed in these breedings. Due to the theological climate in his area, people did not look favorably upon experimentation with animals; hence Mendel chose the garden pea for his experimentation.

Mendel was an astute observer. He began to detect patterns of inheritance in the garden pea having to do with flower color, internodal stem length, pod color and pea shape. He noticed that when he crossed a certain red flowered plant with a white flowered plant, the offspring were all red. Mendel wondered what had become of the trait for white flowers, so he crossed two of his second generation red flowered plants. The results of this cross were in a ratio of 3:1 (red:white). His conclusions were: 1) the factors of inheritance occurred in pairs 2) the factors become separated in reproduction 3) the factors for various traits can be inherited independent of any other factor. For example, the traits causing a plant to be tall or short might have no effect on whether its seeds are smooth or wrinkled.

Mendel died in 1882, never realizing the importance of his work. Eighteen years later in 1900, three other scientists, Hugo De Vries in Holland, Karl Correns in Germany, and Erick von Tschermak in Austria all reached conclusions similar to Mendel. In researching past scientific literature, Mendel's papers were found and he received credit for his life long work.

ACTIVITY #1:

MATERIALS: TWO PENNIES PER STUDENT, MASKING TAPE

PROCEDURE:

1) Have students fix a piece of masking tape on each side of each coin.

2) Label the pennies with a "B" on one side and "b" on the other.

3) Provide the students with handout containing the table (see attachment A).

4) Have students toss the two pennies 50 times and tabulate by slash marks the number of times each combination appears. Tabulate the results of the class at the end of the session and save for Activity #2.

ACTIVITY #2:

MATERIALS: MARKED COINS FROM ACTIVITY #1, TWO NICKELS PER STUDENT, MASKING TAPE

PROCEDURE:

1) Have students mark nickels "T" on one side and "t" on the other side.

2) Provide students with a handout of the following chart (see attachment).

3) Have students toss all four coins and tabulate the results on the chart (see attachment B).

4) Tabulate the totals of the entire class. Evaluate the results in relationship to the sample size and predictability.

ACTIVITY #3:

PROCEDURE:

Students may prepare reports on Mendel's life, including his educational failures, the controversy surrounding his data, and reasons why his work was not recognized.

Kormondy, Edward J. and Bernice E. Essenfeld. Biology: A Systems Approach. Mewnio Park, CA: Addison-Wesley Co, 1988.

Kottler, Malcolm. "Hugo Devries and the Rediscovery of Mendel's Laws." Annals of Science 36 (1979), Pp. 517-538.

Mclaren, James E. and Lissa Rotundo. Biology. D.C. Heath, 1985.

Orel, Viteslav. Mendel Oxford: Oxford University Press, 1984.

Rostand, Jean. Human Heredity. New York: Philosophical Library, 1961. 87092.

Schraer, William D. and Herbert J. Stoltze. Biology: The Study of Life. Allyn and Bacon, 1983.

Toole and Otto. Modern Biology. "Principles of Heredity." New York: Holt, Rhinehart and Winston, 1985. 

Name:___________________________________ Class: __________________________________________
 

Key
 

B = dominate trait--Unattached earlobe, or, ability to roll tongue

b = recessive trait--Attached earlobe, or , inability to roll tongue
 

OBSERVED RESULTS
 

Genotype Phenotype TalliesTotals
 

BB Can roll ________ _________
 

Bb Can roll ________ _________
 
 
 

bb Can't roll ________ _________
 

Class Totals ________ _________
 

Attachment B
 

Di-hybrid Cross (two traits)
 

Key

B = Dominate unattached earlobe

b = Recessive attached earlobe

T = Dominate rolled tongue

t = Recessive unrolled tongue
 

Observed Results
 

Genotypes Phenotypes TalliesTotal
 

BBTT Unattached/can roll ________ ________
 

BBTt Unattached/can roll ________ ________
 

BBtt Unattached/can't roll ________ ________
 

BbTT Unattached/can roll ________ ________
 

BbTt Unattached/can roll ________ ________
 

Bbtt Unattached/can't roll ________ ________
 

bbTT Attached/can roll ________ ________
 

bbTt Attached/can roll ________ ________
 

bbtt Attached/can't roll ________ ________
 

Class Totals ________ ________
 

# of Unattached/can't roll ________
 

# of Unattached/can roll ________
 

# of Attached/can't roll ________
 

# of Unattached/can roll ________