Get out the data table you recorded from the Part 1 of the activity.  Tally the number of times you get for each genotype (RR, Rr, and rr) and record these numbers on the bottom of your data table.  Next, calculate the percentage of each genotype that occurred during this activity.  For instance, if you had 7 RR out of 15 trials, you will need to do division and multiply by 100 to get the percentage.
Again, record these figures on the bottom of your data table.

You should have all the percentage calculated for each genotype at this point.  Before we go any further, I would like you to think about the following questions and record your answer on the back of your data table:
1.  What is the dominant trait in your M&M activity?  Red or white?
2.  What is the recessive trait in your M&M activity?  Red or white?
3.  What are the genotypes of the parents in this activity?
4.  What are the phenotypes of the parents in this activity?
5.  Do a Punnett square based on your answer from #3.
6.  Calculate the percentage of homozygous recessive, homozygous dominant, and heterozygous genotype. 

Finally, how are these percentages similar or different from what you obtained in the M&M activity?  Write your response under the "comments" section of the post.



This activity is designed for you to understand how probability plays a factor when it comes to heredity.  As I mentioned earlier in the previous post, Punnett square allows scientists to make predictions about various genetic problems.  It shows the probability of what might occur.  If you recall from your math class, probability is the chance of something occurring.  For instance, if you flip a coin 100 times, you would expect to get 50 heads and 50 tails.  However, after tossing your coin for 100 times, you actually ended up getting 40 heads and 60 tails instead.  Therefore, Punnett square is only a prediction of the chance.

If you have a sibling, invite your sibling to join you for this activity because you will need someone to record data for this activity.  Here is what you needs: a bag of M&M chocolates and two paper bags.  Pick two colors of M&M from your bag of chocolate.  For example, red and white.  Put 15 red M&M and 15 white M&M into one paper bag and label this paper bag as "Female".  Get another paper bag and put 15 red and white M&M into this bag again.  Label this bag "Male".  These two paper bags with red and white M&M chocolates will represent your heterozygous parents (Rr X Rr).

Have your sibling and yourself reach into each paper bag at the same time and pull out one of the M&M chocolates from the bag.  Remember, the only possibilities that can be made from this selection are: RR (homozygous red), Rr (heterozygous red), or rr (homozygous white). Record genotype and phenotype in the data table then return the chocolate back into the bag.  Repeat the drawing process for another 14 times with a total of 15 trials.

Your data table should look like this:
Trial                  Offspring's genotype                      Offspring's phenotype
1                        RR                                                      Red

Keep your data table for now and we will wrap up this activity in the next blog post.

P.S: You may now eat your chocolates after you record all the data!


We briefly talked about the concept of the Punnett square during class today.  Before I start the activity for today's blog post, I would like to review some basic terms that we went over in class.

So what's a Punnett square?  A Punnett square is a graphic representation that shows and predicts all possible gene combinations in a cross of parents whose genes are known.  When the organism is said to be homozygous for that trait, both the alleles of a gene pair are the same.  There are two possible ways for the organism to be homozygous.  The organism can be homozygous dominant (BB) or homozygous recessive (bb).  However, when the two alleles in the gene pair are not the same, we refer the organism as heterozygous (Bb) for that trait.  Finally, we use the term "genotype" to refer the genetic properties of the allele combinations of an organism while the term "phenotype" is used to describe the physical outlook of the trait.


Let's look at the picture above to understand how the Punnett square is used to predict the results of a monohybrid cross between the homozygous dominant gray-bodied male bunny with the homozygous recessive brown-bodied female bunny.  First, draw a square and divide it into four parts.  Represent the homozygous dominant gray-bodied male bunny with the genotype "BB" and the homozygous recessive brown-bodied female bunny with the genotype "bb".  These letters represent the alleles donated by the Parent (P) generation. Each square then represents the possible zygote allelic combination. This generation the first (F1) generation.

Fill in each box of the Punnett square by transferring the letter above and in front of each box into each appropriate box. As a general rule, the capital letter goes first and a lowercase letter follows.  Based on the Punnett square above, what will be the genotype for the F1 offspring in this monohybrid cross?  Now predict the phenotypic ratios of the offspring. (Remember that phenotype is the physical appearance of a trait.)

Finally, after you have answered the questions above under the "Comments" section.  I would like for you to find out what seems wrong in the picture above.


"Like father like son" is a common phrase that we hear when a boy looks a lot like his father.  Have you ever wonder why?  Up to this point, we have discussed about nucleus, chromosome, and DNA.  As you recalled from the previous entry, DNA is the genetic make-up of your body.  Specifically, there are sections on the DNA called genes that determine your traits.  For instance, there is a particular section on your DNA that determines your eye color, hair color, and you name it.

In this activity, I want you to take a close look at some of your traits.  Record your results on another sheet of paper.

1.  Can you roll your tongue?

2.  Can you make a Vulcan hand sign?

3.  Are you right- or left-thumbed?  Put your hands together, interlocking your fingers.  Which thumb is on top?  Write “right” or “left.”

4.  Do you have dimples?  Look into a mirror and smile.  Do you see any?


Go to your mom and dad.  Ask them these questions and record the result from both of them.  Compare your result to your parent's.  Can you tell who passes on the trait to you?  Reply your conclusion under the "Comments" section.


Look at the pictures below and determine which of the following is of an organism that contains DNA.


What can you conclude from the activity above?  Write your conclusion under the "Comments" section.

Hint:  Based on what we learned earlier, DNA is found inside a special area of the cell called the nucleus.  Therefore, there are only two types of cells that contain nucleus. 


Did you get the question correct from the previous entry?  If yes, then you are definitely rolling.  If not, that's okay. 

Let's begin by reviewing the DNA structure.


First, the double helix structure in DNA is composed of the "sugar phosphate backbone".  DNA is consisted of 4 different nucleotides (chemical building blocks).  They are Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).  However, why are they called base pairs?  As the picture suggests, Adenine pairs with Thymine while Guanine pairs with Cytosine.  Therefore, Adenine and Thymine are one of the base pairs.  Another base pair will be Guanine pairs with Cytosine.  If you are having trouble remember the names for each nucleotides, then try to remember the shorthand for each one.  A pairs with T and G pairs with C (Aunt Tina is Going to Circus).  Can you believe it?  The DNA in your cells have information for your whole body!!! 

Where can you find DNA?  DNA is found inside a special area of the cell called the nucleus.  Due to the size of the cell, each DNA molecule must be tightly packed and condensed because there are many DNA molecules in a cell.  Therefore, the condensed form of the DNA is called a chromosome.  Humans have 23 pairs of chromosomes in each cell.  22 of these pairs are called autosomes which are the same for both male and female.  However, the last pair of chromosome is called the sex chromosome which is different for both female and male.  Do you know the difference between a female and a male sex chromosome?  It's okay If you don't know the answer to this question.  We will discuss this more in details during class.  If you do know the answer, please reply under the "Comments" section.


Before I go into the theme for the next unit, I would like to announce that everyone did very well on the digestive system unit test.  I'm very please with the result.  :)  Keep up the good work!!!

The theme of this unit will be on Genetic and Heredity.  To begin this unit, we will first look at DNA.  What's DNA?  DNA is a long string of genetic codes in a cell.  These genetic codes are composed of chemicals building blocks called nucleotides that lined up in a specific order.  It looks something like this:


What do you notice about the structure of this DNA strand?  Yes, DNA is double stranded as the picture implies.  It is also known as the double helix structure.  I mentioned about chemicals building blocks in the DNA earlier in this entry.  Where do you think these chemical building blocks are located?  Reply your answer under the "Comments".



    Ms. Pan is a 7th grade Science teacher at XXX Middle School. 

    Ms. Pan is both a scientist and an educator, but she likes the role of a teacher more than anything else. 

    The purpose of this blog is to provide online learning discussion and stimulate thinking prior classroom activities.
    For students, please check this blog on a daily basis to participate in discussion.
    For parents, please check this blog on a regular basis to see what your children are learning in the classroom.


    April 2009

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