Dihybrid Cross

For homework tonight, we are learning about dihybrid crosses, which involve two traits. I have made an example question below.



In this example, the a homozygous dominant father (TTZZ) and a homozygous recessive mother (ttzz) breed and have offspring. All of the offspring, F1 generation, are heterozygous (TtZz). Having a tan (T) is the dominant trait and not having a tan (t) is the recessive trait. Also, having a zigzag tattoo (Z) is the dominant and having no zigzag tattoo (z) is recessive.

The genotype ratio is 1 TTZZ: 2 TTZz : 2 TtZZ : 1 TTzz: 4 TtZz : 1 ttZZ: 2 Ttzz : 2 ttZz : 1 ttzz, and the phenotype ration is 9 tan/zigzag tattoo: 3 tan/no tattoo: 3 no tan/zigzag tattoo: 1 no tan/no tattoo.

Below is a cool example of another dihybrid cross. Four different cats are produced, with the color and the length of tail changing.

Monohybrid Cross

In the last class, we learned about a monohybrid cross. For the most part, I understood how to do it. I got a 5/5 on my quiz, so that should show that I know something. I think that I have cleared up any uncertainties by now.

An example of a monohybrid cross that I will make up right now involves the breeding between a homozygous right handed father (RR) and a heterozygous right handed mother (Rr), with the dominant trait being right handed (R) and the recessive trait being left handed (r).



As shown above, this match results in a genotype ratio of 2 RR: 2 Rr and a phenotype ratio of 4 right handed : 0 left handed.

Test & Lab Report

To study for my Unit 3 Test, I re-watched all of Mr. Quick's videos, watched some other videos on youtube, and went to Mr. Quick's Sunday review session. When I took the test, I felt pretty confident about my written response, but not to confident about the first ten or so multiple choice questions. I think that I should have spent more time practicing writing DNA sequences, and the replicated or mRNA sequences that came with it. I think that I knew how to do it, I just could not get my brain to work at the time. When taking the test, I was still a little stumped on the 5' to 3' and the 3' to 5'. However, after looking at my mistakes I believe that I understand it clearly now. I also should have practiced finding the amino acids that went with the mRNA codons.


As for the lab report, this one did not take nearly as much time as the last one, but it was still pretty time consuming. I think that the reason that it still took a long time for me was that I was still a bit confused on what my results showed. Our purpose of the experiment became a lot more clear once we talked about operons, but is was still a bit confusing. After reading an explanation, it was all cleared up for me, and I was able to write my report. I think that I wrote too much, but that is because I had to cover a lot more topics than just operons. below is the link to my lab report.

https://sites.google.com/site/blakeshonorsbiologysite/hb-standards/3-dna-structure-and-function/--pglo-lab-report

Operon System

The class before the test, we learned about the Operon System. An operon can come in two different forms. It can be either repressible or inducible.


In a repressible operon, the repressor is initially inactive, and so the RNA Polymerase can go down the DNA strand and create a complementary mRNA strand (transcription). Then, it goes through RNA processing and through transcription and eventually becomes a protein. The protein can then act as the co-repressor, and activate the repressor.




In an inducible operon, the repressor is initially active, so the RNA Polymerase is blocked from going down the strand and eventually creating a protein from that gene. When an inducer, such as arabinose for the pGLO lab, is added, the repressor pops out of the operator and becomes inactive. The RNA Polymerase then goes down the DNA, and through Transcription, RNA Processing, and Translation, the a protein is made. This protein is an enzyme, arabinase, that eats the sugar, arabinose. When all of the sugar, inducer, is eaten up, the repressor becomes active again, and blocks off the RNA Polymerase.

What Do These Photos Mean?

     Using Survival of the Sickest and Your Inner Fish, we have to describe the following two photos.

     This flower has most likely developed its colors for more reasons than one. If I had to take an educated guess, I would say that it developed bright colors to attract bees, so that it can be pollinated. Another possibility is that its colors act as a warning sign, causing less animals to eat this flower for fear of being poisoned. It discussed something like this in Chapter 4 of Survival of the Sickest, when is said that when plants containing phytoestrogens are consumed by animals, the estrogen-like compound affects the reproduction of these animals, reducing the number of animals that eat that plant. 

Rewriting what I wrote in the previous blog post, "Failure of “Sonic hedgehog” to turn on properly can result in extra fingers, paddle hands. Similarly, malfunctioning ZPA results in malformation in hands". This is different than what the scientist in Chapter 3 of Your Inner Fish were doing. What the scientist were doing was moving the ZPA patch from one side of the bud, which in later development is the hand, to the other side, resulting in an exact duplication of the fingers, not like what is seen above, but rather what is seen below.

     Notice that in the experiments done in this chapter, the two ends of the arm where mirror images of each other.