I believe adamantly that science is well taught only if there is a careful pairing of labs with theory. Sometimes it is difficult to think of labs to pair with the theory. Thinking of a lab to pair with the theory for how the reproductive system works in a middle school textbook was definitely one of those cases. I was so proud of myself when I thought of this lab to use in RSO Biology 2. I was pretty disappointed when neither Kate, my publisher, nor Sean liked this lab. (It is actually interesting to me how often these two agree.)
I love this lab. You should know though, before I was a science nerd, I was a math nerd. The fact that I love this lab and did not realize how difficult it was going to be for people who don’t love math as much as I do highlights this like nothing else can. Seriously, in my college math classes, I used to work ahead in my textbooks before the semester started. To this day, if I really need to unwind Ken Ken does the trick.
I am very busy writing Astronomy and Earth Science 2 right now, but I like to post weekly on my blog. So I decided to begin releasing some of the labs and lessons that didn’t make it into my books. A gift from me to you! If you have a high school student studying biology, this is a great lab. If you have a middle school student who is crazy about math they might like this too. Or maybe you’re an adult and you just find this an interesting topic. If so, why don’t you give this lab a try. I will be posting the answer key with colored photos tomorrow.
The illustration was made for this lab. It is such a great illustration that it did still find its way into Biology 2. I am working with a different illustrator for Astronomy and Earth Science who is equally as talented. I have been very lucky with the illustrators who have worked on all my books. (I will be posting a lab and lesson that did not make it into RSO Chemistry 1, a lesson that did not make it into RSO Biology 2, and another Biology lab that I thought of and wrote too late for it to make it into the book over the next couple of months.)
People come in all shapes and sizes. We have different hair color, eye color, and skin color. We are all so different. Unless you have an identical twin, you do not even look exactly like your siblings. How does that happen?
Humans are diploid. They have 2 x 23 chromosomes equaling 46 chromosomes total, 2n = 46. That is two sets of 23 chromosomes. One set comes from the mother’s egg and one set from the father’s sperm.
You are going to determine how many genetically different gametes a male and female organism could make with 3 chromosomes in each set, 2n = 6. That means that the gametes of this organism each have 3 chromosomes. Remember the gametes of diploid organisms are haploid, n. That way when the male and female gametes fuse during fertilization their offspring have 2n chromosomes, the same as their parents have. After you have determined all the possible gametes these two parents can make you are going to look at all the possible combinations that could occur during fertilization.
It is random chance, which chromosomes are in a gamete. Your mother and father got half their chromosomes from their mother and half from their father. That means you have chromosomes from your grandparents in you. Each of the two gametes that made you might have had only chromosomes from your grandmother, only those from your grandfather, or each gamete might have chromosomes from both your grandmother and your grandfather.
- Four different colors of markers, pencils, or pens
- Lab Sheets, 3 pages, two of the lab sheet are attached at the end of this post as Adobe pdf files (if you need them in a different format, email me at email@example.com and I will send them to you in the format you request.)
- Select two colors to use on the female gamete worksheet. One color represents the grandmother’s chromosomes and one color represents the grandfather’s chromosomes. Using the numbers 1, 2, 3, list all the possible combinations of chromosomes for meiosis Metaphase I, this is the first column of circles on the sheet. For example, the first gamete might have all the numbers in one color on one side and all the numbers of the other color on the other side. In that case, the resulting gametes will only get chromosomes from each grandparent. Three sets of homologous chromosomes can line up four different ways. Remember 1 can only pair with 1, 2 with 2, and 3 with 3. It is the color pairings that will vary.
- The chromosomes will separate, forming two gametes. Each will have only the chromosomes that were on their side. Under the two columns titled Gametes, write the number of the chromosomes, 1, 2, 3. Make sure you get the correct colors in each gamete.
- Do the same thing for the Male Gametes Lab Sheet using two different colored pens.
- Cut out all 16 gametes. What are all the possible combinations of genetically distinct zygotes that could form from these gametes?
- Make a pile with the female gametes. Lay the male gametes out like cards so you can see all eight of them. Take one female and make all the possible different combinations with the eight male gametes. Do this with each female gamete. Remember, only one female and one male gamete can combine.
- Complete the questions on Page 3 of the lab sheets.
*This lab does not go through the entire process of meiosis. The two gametes that form from each of the two cells after cytokinesis II have the same complement of chromosomes as those from cytokinesis I. From a statistical standpoint, these duplicate gametes are not significant.
Why Are We All so Different? Lab Sheet, page 1
- Assuming no mutations, how many genetically different offspring can two parents with 2n = 6, 3 pairs, of chromosomes have?
- Humans have 23 pairs of chromosomes. Do you think two human parents can have more, less, or the same number of genetically different offspring as an organism with 3 pairs of chromosomes? Defend your answer.
- There is a process called crossing over. During meiosis, parts of homologous chromosomes can cross over each other, break off, and each reattach to the other chromosome. How do you think this affects variability in an organism’s gametes?
Bonus: There is a mathematical rule for how many different types of gametes an organism can produce. Think about this lab and how many different gametes were formed. Can you figure out what the rule is? Hint: The rule involves an exponent.
Using the rule, you can peek at the answer if you need to, how many different types of gametes can one human make. Aren’t you glad we didn’t use two humans for this lab?
Fraternal twins often look very different. Explain why based on the results of this lab.
Lab Sheet, page 2 female gametes variability lab
Lab Sheet, page 3 male gametes variability lab