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Genes for the Whole Family - Mendelian Genetics

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About this Unit

Before performing the activity in this unit students should be familiar with the following concepts.

  • Basic Mendelian genetics and the concept of dominant and recessive traits.
  • Punnett squares (to predict possible genetic outcomes).
  • The difference between heterozygous and homozygous genotypes.

Teacher's Notes

This activity is surprisingly challenging. It generally takes several tries to produce the desired result.
Keep track of how many attempts you make in order to produce a homozygous BB pair of rabbits.

Of course because of the probability nature of selective breeding some students will, by pure chance, produce a suitable result after a few generations on their first try. Repeat the process and see if the results are the same.

The emphasis here is two-fold:

  1. Simple Mendelian genetics.
  2. The difficulty (and inefficiency) of selective breeding.

Activity: To Explore Genetic Inheritance ("Brainy Bunnies")

Materials Needed

  1. A single die (from a pair of dice).
  2. A styrofoam cup, in which to shake the die.
  3. The Genetic Game card (included in this activity).
  4. Coloured pencils.
  5. Lots of paper.

The Genetic Challenge

Two isolated Pacific islands are discovered to have indigenous rabbits, (a very rare species), which are on the verge of extinction. One island has only male bunnies left, the other island has only female bunnies surviving.

The problem is that the males, (dumb bunnies), are not smart enough to survive on their own and females need males in order to reproduce and save the species.
You are given one of each gender. Your task is to attempt, by selective breeding, to create a generation of truly "smart" bunnies.

The bunnies, (the rabbit kind!), come in two genotypes, female bunnies which are incredibly smart, (brainy - a dominant trait BB), whereas, the male bunnies are... ummmm... well let's say, not quite as smart - a recessive trait bb).
Each is homozygous, the male has genotype bb and the female has genotype BB.

Bunnies 1

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Your First Generation

To help you on your quest to save the species, the first generation of offspring has been provided. All offspring of your pair of rabbits will be heterozygous, that is, Bb or equivalently bB.

The question is, will it be possible to inbreed several generations of offspring until only homozygous BB pairs remain?

Your challenge will be to try and create a breeding pair without any recessive genes whatsoever using the toss of a die to simulate the "laws of chance".

You begin with a male and female heterozygous pair of rabbits.

Bunnies2

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The Genetic Simulation Card

Nature often acts in ways that seem to be governed by the Laws of Chance and Probability. To simulate this effect we will roll a six-sided die to determine some of the genetic outcomes of our breeding challenge.

You will need to print out a copy of the Genetic Simulation card.
The die scoring has been set up to provide a 50/50 chance of selecting either a dominant or recessive allele.

The default means that in the case of a homozygous parent you must apply the appropriate allele since there is really no choice involved.

Dice

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Here's How It Works

Rule Number One:

You can only have 3 (three) offspring per breeding pair.

Rule Number Two:

Use the die and the Genetic Simulation card to determine the genotype of each offspring. To "roll" the die, drop it in the styrofoam cup, cover the open top with the palm of your hand and shake the cup vigorously then look inside to determine the outcome. Keep the die in the cup at all times... don't let it fall on your desk or on the floor.

Rule Number Three:

Refer to the Genetic Simulation card to determine the genotype of the offspring according to the following:

  • First shake of the die determines the allele from the MALE parent.
  • Second shake of the die determines the allele from the FEMALE parent.
  • Third shake of the die determine the gender of the offspring.
  • Fourth shake of the die determines the breeding success.

Roll the die four times to determine the breeding outcome for each offspring.

Rule Number Four:

If you produce a breeding pair then you may continue the
process for successive generations.

Rule Number Five:

Continue until your species becomes extinct or you succeed in
producing a homozygous breeding BB pair. Note: remember a
homozygous breeding pair bb is doomed. They will become
extinct.

Rule Number Six:

Conditions

  1. A given pair of bunnies can only breed once.
  2. Breeding between generations is not permitted.
  3. Female bunnies may have multiple litters of offspring, subject to condition number 1.

Example

The example shown here is taken from the students' worksheets, shown here.

Every group's worksheets will be slightly different barring an unusual statistical coincidence.

Usually several tries are required before success is achieved.

Example1

In this example, the genotype chart begins with the 1st generation breeding pair.

The die and Genetic Simulation card have been used to generate the genotypes and genders of the 2nd generation offspring. The results are shown.

Squares denote males and circles denote females.

The result was two viable breeding pairs. These two pairs have been set up to show that there are six possible third generation offspring.

To continue the simulation, the die will need to be cast to determine the possible genotypes and genders of each of the six offspring. Breeding pairs will be identified and the process will continue until the goal of producing a homozygous BB breeding pair has been attained.

Sample Generation

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Your Turn

  • Begin by drawing or printing a copy of the Starter Chart. This is your initial breeding pair. Their genotypes are shown.
  • Use the die and the Genetic Simulation card to create genotypes for their offspring.
  • If you succeed in producing a breeding pair(s) then draw or print copies of the Generation Chart and continue to create successive generations of rabbits until the object is reached.
Starter Chart Generation Chart

Starter Chart

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Generation Chart

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  • Work in teams of two or three students.
    One student can act as the die shaker, another can decode the results from the Game Simulation card, and the third student can fill in the genotype charts for each generation.
  • Each group's worksheets will be slightly different barring an unusual statistical coincidence.
  • You must restart at the beginning if your family tree expires.
  • Keep track of how many tries (restarts) and how many generations it takes to produce a homozygous BB breeding pair.

Example2

Observations and Conclusion

Were you successful? If not try again. How many generations were required to achieve a homozygous BB breeding pair?
Compare your results with others.

Discussion

  1. What would be the effect of having only two offspring per breeding pair? What about four offspring per breeding pair? Set up a simulation and try it.
  2. Rabbits mature rapidly and have fairly short gestation periods. They breed and multiply rapidly. Some animals take many years to reach reproductive maturity and have relatively long gestation periods. Comment on the potential impact of genetic engineering and cloning.

Read the following articles. Mapping the Future of Halibut Culture. Discover how scientists at the National Research Council of Canada Institute for Marine Biosciences are investigating genetic mapping as the key to improving the productivity of Atlantic halibut.

Plant Biotechnology - Crops for Enhanced Human Health. Read about research being done at the NRC Plant Biotechnology Institute.

Extended Activity: Genetically Transferred Traits

  1. Use salt substitute (sold in grocery stores). Put a dab of salt substitute on your tongues. Keep glasses of water on hand! How many students have a very bitter taste in their mouths (the "tasters")? How many don't (the "non-tasters")? About three out of four people have a dominant gene that makes them tasters. How does your class compare? Does age make a difference? Boys versus girls?
  2. Use the charts below as a guide. Do a family survey of inherited dominant and recessive traits that you have learned about in class.

Genetic Sample (Mom's Side of the Family)

RELATION
Mother's side
of the family
Tongue rolling
(Y or N)
Earlobe attachment
(Y or N)
Hitchhiker's thumb
(Y or N)
Widow's peak
(Y or N)
ME        
My Brother        
My Sister        
My Mother        
Uncle        
Aunt        
Grandmother        
Grandfather        

Genetic Sample (Dad's Side of the Family)

RELATION
Father's side
of the family
Tongue rolling
(Y or N)
Earlobe attachment
(Y or N)
Hitchhiker's thumb
(Y or N)
Widow's peak
(Y or N)
ME        
My Brother        
My Sister        
My Mother        
Uncle        
Aunt        
Grandmother        
Grandfather        

Supplementary

Gregor Mendel (1822-1884)

Mendel's experimentation involved pea plants. He studied flower characteristics such as height variation, colour of the flowers, and the different textures of the seeds. From this, he further studied inheritance, which is the process of passing characteristics to the further generation.

His research lead to several conclusions:

  1. The characteristics of any organism are passed from parent to child by pieces of information called genes. Every gene represents a single bit of information containing one characteristic.
  2. Alleles are two or more genes that carry a piece of information about a single characteristic. One of the allele pair may be for smooth cheeks, and the other may be for dimples. Alleles are usually found in pairs, one of which is dominant, or overpowering, and one of the alleles recessive, which is masked by the dominant.
  3. In reproduction, each gamete, or reproductive cell, (sperm or egg) has only one of the allele pair present.
  4. If a dominant and a recessive allele are both present, the
    individual will be affected by the dominant allele.

T. H. Morgan, an American scientist later showed that Mendel's rules of genetic inheritance applied to all plants and animals (including humans).