Objectives:
1) Generate interest and curiosity regarding heredity
2) Engage students in re-enacting Mendel's pea plant  experiments to: a) appreciate the scientific process;
b) be aware of his contribution to genetics; c) understand how simple traits are inherited and  are able to use genetic notation

Point A - Generate interest and curiosity regarding heredity.

The plan:  Using resource 1, students will be introduced to the nature vs. nurture debate     

Resource 1 - Nature vs. Nurture:  Are humans the product of the genes they inherit, or are they moulded by the environment in which they live? Many  studies have been made on the expression of specific traits in identical twins compared with the expression of those traits in fraternal twins. Have students discuss how these studies are  expected to tell something about genes versus the environment. Make an overhead of the following table.                 

___________________________________________________________________
     
Discuss whether the class thinks the trait is mostly the result of genetics or the environment or both.  In addition,  intelligence is one trait about which people have argued a lot.  People have observed that smart parents tend to have smart  children and not-so-smart parents have not-so-smart children.  To some people this means that intelligence must be genetic.  Do you agree?

Evidence of understanding:  Students will form opinions and debate amongst themselves, taking into account the given data and their own experiences.  Students should be able to refer to the data and defend their beliefs.
LINK:  Our focus in this unit is genetics -- the study of  how characteristics are inherited. But always keep in mind that the environment plays a role. That is why outcomes don't always match our expectations.  Interesting tidbit: The characteristics of offspring are determined by the parents, right?  The ancient Greeks believed that the man was responsible for the child (the "seed") and the woman served as a carrying place (the "garden").  She had no contribution to the child whatsoever.
Point B - Students know and appreciate the scientific method.

The plan:  Read worksheet section Mendel's Experiment - Part 1 and answer question #1.  This activity takes cognitive overload into account.       It emphasizes understanding before terminology and notation.

Mendel's Experiment - PART 1 : Students read the short reading and answer the related question.  This can be done in groups or individually. The teacher leads a class discussion on the topic.

Evidence of understanding:  Students are able to identify the components of good scientific processes in Mendel's experiment.     

Point C - Students know and apply good scientific methods.

The plan:  Work through worksheet section Part 2 which involves making predictions, observations from data cards and conclusions.

Mendel's Experiment - PART 2 :
1) In groups of 4, students choose a pea plant characteristic on which   they wish to focus.  
2) They work through Part 2 of the handout.
3) To make an observation, the group receives an envelope of 30 data  cards from the teacher.  On the front of each card is a picture of a pea plant exhibiting a certain characteristic (e.g. tall).  On the back, the card is marked with the generation (F1 or F2).  Students tally the number of plants that express the two possible forms of the trait for the F1 and F2 generations.  Hypotheses are to be made before observations.
4) After completing the section, students receive the actual F2 results  from Mendel's experiment.  They attempt to explain their results.
     
Mendel's Actual F2 Results:

 

Source: Raven, P.H. and G.B. Johnson. Understanding Biology. Times Mirror/Mosby College Publishing, Toronto, 1988. (p.209)

Evidence of understanding:  Students are able to complete the worksheet to the teacher's satisfaction. Discussion about the conclusion to the experiment will take place after genetic notation is taught.

Point D - Students understand a) how simple traits are inherited and b) are able to use genetic notation (genotypes).

The plan: Mendel's Experiment - Parts 3 & 4
GENETIC NOTATION (Part 4)
1) Introduce terms: genotype, allele, dominant, recessive and redefine  purebred and hybrid in terms of genetic notation.
2) Practice writing the genotype for an example.
Example: On the planet Ylogoib, blue antennae are dominant over yellow  antennae. The dominant allele is represented by the capital letter  of the dominant trait.  The recessive allele is represented by the
llower-case letter of the dominant trait.  
Let B represent blue antennae.
Let b represent yellow antennae.
BB = purebred blue
Bb = hybrid blue
bb = purebred yellow

Evidence of understanding:  Students complete the genotypes for their chosen trait, after being told which trait is dominant. (Mendel's experiment, Part 4)
CONCLUSION (Part 3)
3)  A suggested line of questioning to help students reach the same conclusions as Mendel is as follows:
a) Compare the phenotypes of the F1 generation with the F2 generation.  What do you notice?  What is the phenotypic ratio in F2?  (F1 = all same, F2 = some of each,  F2 is 3:1)
b) What are the genotypes of the P generation?  What are the genotypes of the F1 generation? (This should be written already, with knowledge of what is purebred and hybrid)
c) Compare the F1 genotype with its parents. (Has one of each: can expand and draw out Conclusion #1)
d) What is the source of each allele in the F1? (each parent)
e) What happens to the parents' alleles when they cross?  (they separate - introduce the term "gamete")
f) How are the parents' alleles distributed? (each parent gives one allele - Conclusion #2)
Conclusion #3 is given to the students.

Define Mendel's Law of Segregation and Law of Independent Assortment

Conclusion of Mendel's Experiment:
A 3:1 ratio among F2 offspring was possible if:
1. F1 contained two separate copies of each hereditary factor, one of  these being recessive.
2. The factors separated when the gametes were formed and each gamete  nly carried one copy of each factor.  The factors separate independently of one another and this is known as the Law of Independent Assortment.
3. Random fusion of gametes occurs at fertilization.

Evidence of understanding: Students can answer the oral questions and  post-lab questions. Ask students to write down something they do not understand; collect the papers to get an idea. Address the questions to the whole class.           

HANDOUT FOR STUDENTS                                                         

Mendel's Experiment

PART 1

Title: Heredity in Pea Plants (Pisum sativum)     
Purpose: To observe whether blending was the true method of inheritance
Method:
Mendel did preliminary studies with animals and plants before he chose the pea plant to test heredity.  Peas were a good choice because they normally self-pollinate which means that they are true breeding (or purebred) and the offspring are identical to the parents.  Mendel prevented self-pollination by tying bags over the stamens of the plants.  Peas may also be cross-pollinated which reveals the effect of combining two purebreds to make a hybrid.  In addition, pea plants are easy to cultivate and have a short generation time.
Mendel selected 22 varieties of the Pisum - the edible pea.  He grew and tended these plants himself in the Monastery gardens where he was a priest.  By simply observing the objective facts, Mendel was able to record results independent of any personal beliefs that he had.  Altogether, Mendel studied the inheritance of seven simple and easily distinguishable traits.  They were: seed colour, flower colour, pod colour, pod shape, seed shape, stem length and flower position.  For each experiment, he observed as many offspring as possible.  For one characteristic he counted up to 8023 peas!  Due to his mathematical background, Mendel´s breeding experiments had a statistical basis.  He used probability to interpret his results.
The initial experiments involved crosses between two purebred strains which only different in one trait.  These were called monohybrid crosses.  The original parents are denoted as the P (parental) generation.  The first generation of offspring is denoted as the F1 (filial) generation, and the second generation of offspring as F2.  

Question: Defend Mendel's experiment as an example of good scientific processes.  What makes his results dependable?

PART 2

Choose the pea plant trait that you are going to study.

Trait: 

Mendel's first step was to cross (or "mate") two purebred plants with the two different characteristics of the trait.

P generation (cross #1)
Write the two traits:  purebred                x   purebred                 
What do you think the phenotype of the offspring will be?  Phenotype is the appearance of the organism --what trait they exhibit.  Will they all show one trait or the other?  Or some of each?

     Hypothesis: ...............................................................................................................................
................................................................................................................................................................
................................................................................................................................................................
     Observations: ...........................................................................................................................
...............................................................................................................................................................
..............................................................................................................................................................
..............................................................................................................................................................


The offspring are the F1 generation and they are hybrids.
Next, Mendel took two hybrids and crossed them.

F1 generation (cross #2)

            hybrid                  x   hybrid                  

     Hypothesis of offspring phenotype (F2 generation): ......................................................................
......................................................................................................................................................................
.....................................................................................................................................................................
     Observations:.................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
What was Mendel's actual data for the F2 generation?




Does it match yours?  Look at the ratios.  Explain why this occurs.






PART 3

Conclusions:

1.                                                                          

                                          

2.                                                                          

                                                                          

3.                                                                            

                                          

PART 4

Genetic Notation

Look at the trait you studied.  Which one is dominant?

Dominant:                          

Recessive:                         

Write the representation statements for the alleles:

     Let          represent                  .


Write the genotypes for both parents, and for the F1 generation. (remember the F1 generation is hybrid)

POST LAB QUESTIONS

          1.On the planet Xorbat, purple skin is dominant over green skin.
           Write the genotype for an individual who is:
          a) purebred purple skin  b) hybrid purple skin c) purebred green skin
          d) Is it possible to have an individual who is hybrid for green skin?  Why or why not?

2. In dogs, wire hair is dominant to smooth hair.  If a purebred wire-haired dog is bred to a smooth-haired dog, what will be the hair condition in F1?  Show the phenotypes and genotypes of all individuals.

     3. In tigers, orange fur is dominant over white fur.  A white cub has orange-furred parents.  What is the genotype of each parent?

          4. What kinds of gametes will be produced by the following genotypes?      a) Aa       b) EE  c) kk  d) Tt

Solutions:
1. a) PP  b) Pp  c) pp  d) No, a hybrid individual has 2 different alleles (Pp).  Since purple is dominant, only that trait would   be expressed.  Only 2 recessive alleles (pp) would allow the expression of the green colour.

2. Let W represent wire hair.  Let w represent smooth hair.  The purebred wire haired dog would be WW, the purebred smooth-haired dog would be ww.  The F1 offspring would be wire haired, Ww.

3. Let O represent orange fur.  Let o represent white fur.  The cub is white, therefore it must be oo.  Since the parents are orange,  neither of them can be oo.  They each must have an O.  So the parents are  both Oo, giving one "o" allele each to the cub.

4. a) A and a  b) E  c) k  d) T and t