Tutor profile: Alex Y.
A 70-year-old white male presents to his primary care physician with a complaint of rectal bleeding. He describes blood mixed in with the stool, which is associated with a change in his normal bowel habit such that he is going more frequently than normal. He has also experienced some crampy left-sided abdominal pain and weight loss. He has previously been fit and well and there was no family history of GI disease. It is later found with a colonoscopy that he has a malignant colon cancer. Which of the following cell defects would NOT be expected to result in possible malignant (cancerous) cells? A) A mutation preventing DNA replication B) A blockade in apoptosis C) A decrease efficacy of DNA polymerase fixing errors of replication D) Inactivation of several tumor suppressor genes
This is more of a hybrid between a medical school question and an MCAT question, but those of you preparing for the MCAT can also benefit from this type of question. A good general strategy is to read the PRIMARY QUESTION to figure out what is the important part of the question. Because this is asking you how cancers come about at a cellular level, the rest of the story, which is just telling you that our unfortunate gentleman has cancer, doesn't really matter. So now, we have to remember all of our things about cancer. Cancer happens when we have problems within our DNA. Our DNA usually has an ability to fix itself before replicating. If there is an unfixable problem, the cell will either kill itself (apoptosis), or have checkpoints of (tumor suppressors) that stop the cell from dividing, stopping growth of a tumor. At least one, and usually multiple, of these mechanisms will be defective in cancer. This rules out B (stopping cell from sacrificing itself), C (lost ability to fix itself), and D (stoppage tumor suppressors), as these WILL be found in cancer. Mutation preventing DNA replication is actually good for preventing cancer. Why? Cancer is massive division of cells. If we can stop that from happening, that essentially stops cancer at the beginning. If only we could figure out a drug or therapy that could fix that...
If brown eyes are co-dominant with blue eyes, and make hazel, what is the likelihood that someone with brown eyes and blue eyes will have a child with brown eyes? Blue eyes? Hazel eyes?
Hazel eyes...what a rarity! If only we could figure out how to get people to have specific eye colors in real life... But to answer this question, we need to first figure out what CO-DOMINANCE means. Going back to basics, we need to first know other terms. GENES are part of your DNA that will determine what your body will become. Each of your genes have two ALLELES, one from mom, and one from dad. DOMINANT alleles will mask out other traits and RECESSIVE ones will be hidden unless both are the same. CO-DOMINANT alleles are when mom and dad's genes mix together to have something in between. This is why brown and blue mix to make hazel (at least in our example). So we need to see what our probabilities are by making a PUNNETT square, which is kind of like a multiplication table. B = brown b = blue Bb = hazel We know that our parents here are BB (fully brown) and bb (fully blue) and that they can't be a different combination (Bb) or else they'd have hazel eyes. B B b Bb Bb b Bb Bb After "multiplying", we end up having Bb for all of our children. Meaning we would have everyone with hazel eyes! Maybe then it wouldn't be so rare. Too bad eye color is so much more complicated than just these one genes, like so many of our other genetics are.
In a graph, find the distance between the two points (3,0) and (6, -4)
The typical formula for the distance between two points (x1, y1) and (x2, y2) is the square root of ((x2-x1)^2)) + ((y2-y1)^2). This formula is usually difficult for some people to remember because it's so many numbers and letters. So I think it's usually easier to come up with WHY or HOW this formula came to be. It makes it a little bit easier for me to remember. If you draw a line between the two points, it will usually be diagonal. By using your graph, you can make this into a right triangle using a horizontal and vertical line to connect the dots. The distance you are trying to measure now becomes the hypotenuse for your triangle. The way we figured out this distance was a^2 + b^2 = c^2, which is essentially what we are doing here. Simply speaking, "a" can be your horizontal difference (x2-x1) and b is your vertical difference (y2-y1). By plugging in these numbers, and putting a square root on each side, that is how we get the very first formula. I find that this is easier to remember than some random x's and y's put together because it paints a picture that we are more familiar with. Now, we've made it so that our distance will be 3^2 + 4^2 = 9 + 16 = 25 = c^2 This makes C = 5, which is the distance between our points.
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