NUR 590 Discussion: Genetic Makeup Of The Organisms
PLEASE REMEMBER THIS IS A HIGH SCHOOL ASSIGNMENT SO DON’T MAKE IT TO
COMPLICATED
Now that you’ve developed an understanding of genotypes and phenotypes, it’s time to put these skills together and learn how to use them in completing and reading punnett squares. This assignment will help you do that.
Before you complete this assignment, you should make sure you’ve watched the “Personal Tutor – Punnett Squares” video on McGraw Hill. This video does a nice job of showing how to complete punnett squares. To locate this:
- Sign into McGraw Hill
- Navigate to Unit 3 –> Module 10 –> Lesson 1
- Click on “Expand All”
- Scroll down until you see a pink square/icon titled “Personal Tutor – Punnett Squares”.
- Click on the pink icon and watch the video. If you need to, take notes as you watch.
After you’ve watched the Personal Tutor Video, click here to watch me solve one of the questions in this assignment, showing how to complete and read the punnett square.
Here are a couple things to know/keep in mind as you work:
- Genotypes are classified as either homozygous dominant, homozygous recessive, or heterozygous.
Here is an example:
- AA = homozygous dominant(homozygous, because both letters are the same case, and dominant because they are the dominant allele/uppercase letter)
- aa = homozygous recessive(homozygous because both letters are the same case, and recessive because they are the recessive allele/lowercase letter)
- Aa = heterozygous (heterozygous because one allele is dominant and the other is recessive. Also, both letters are a different case. One is uppercase, the other is lowercase).
Genotypes are considered purebred if they are homozygous and hybrid if they are heterozygous.
- Traits can skip a generation. This doesn’t mean that one parent has the gene, their kids don’t, and suddenly their grandkids do. It means that a generation can carry a trait without expressing it. Look at the punnett squares and example below to see how this works.
Here is a real example from my own life. My mom has blue eyes. The allele that codes for this is recessive. My sister has brown eyes and so does her husband.. but my niece has blue eyes. In this example, B represents the dominant allele (brown eyes), and b represents the recessive allele (blue eyes).
There are three possible genotypes: BB (brown), Bb (brown), and bb (blue). How is it possible for my niece to have blue eyes if my sister and her husband don’t? Out of the three possible genotypes (BB, Bb, and bb) we know that both my sister and her husband do not have the genotype bb, because if they did, their eyes would be blue.
This means their genotypes are either BB or Bb. I could use punnett squares to try each possibility to see what the outcomes might be:
Possibility #1 Mother = Bb, Father = Bb
| B | b | |
| B | BB | Bb |
| b | Bb | bb |
In this cross, there would be a 25% chance that their offspring would have blue eyes, because this is the outcome for 1 of the 4 possible combinations.
Possibility #2 Mother = BB, Father = Bb (or Mother = Bb, Father = BB)
| B | b | |
| B | BB | Bb |
| B | BB | Bb |
In this cross, there is a 0% probability that their offspring would have blue eyes, because this is the outcome for 0 of the 4 possible combinations.
Possibility #3 Mother = BB, Father = BB
| B | B | |
| B | BB | BB |
| B | BB | BB |
In this cross, there is a 0% probability that their offspring would have blue eyes, because this is the outcome for 0 of the 4 possible combinations.
Looking at these punnett squares, we can tell that both parents must have the Bb genotype. This means that they both inherited the recessive b allele from one of their parents, they carried it with them but did not express it, and they both passed this onto my niece who ended up with the genotype bb and blue eyes. This is how a trait, such as blue eyes, can “skip” a generation.
After you’ve had a chance to:
- Watch and listen to the Punnett Square Personal Tutor video
- Watch and listen to my explanation of how to start the assignment.
- Read through the “things you should know” (above)
Then go ahead and give this assignment a shot. You can find the PDF for it right here. As usual, port it into Notability, complete it there, and then bring it back here to turn it in.
