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Avinash E.
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Biology
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Question:

Question: A 38-year-old mother has two different alleles for the X chromosome, A1 and A2; the father's X has allele A3.Answer the following questions: A) Their son is found to have a single bar body in the nucleus of his cells. He was genetically tested and found to have both the A1 allele and the A3 allele. Describe in detail the defect in meiosis that would make this possible. B) Their doctor was surprised that the A3 allele is found in the son's cells, why would this be the case? C) What genotype/s was the doctor expecting to find based on his knowledge of when non-disjunction is most common? A narrative or a diagram is an acceptable answer. D) Extra or fewer chromosomes are one of the more common abnormalities that are observed in a fetus, but most of them are not viable or lead to a stillborn child. This child is healthy and relatively normal. Why, in this case, is the extra dose of genes less of a problem for the child's health? E) An extreme example of aneuploidy is XXXXY. How many Barr bodies would be present in the cells of this person?

Avinash E.
Answer:

A) solution: Ideal meiosis possibilities for a boy child are shown below case a: Xf1Xf2 + XmY = Xf1Y + Xf2Xm case b: Xf1Xf2 + XmY = Xf2Y + Xf1Xm But in our case, the son is found with both A1 and A3 alleles. So there is a non- disjunction during recombination resulting in aneuploidy. case 1: Xf1Xf2 + XmY = Xm O+ Xf2Xf1 Y (chance of happening) case 2: Xf1Xf2 + XmY = Xf1 O+ Xf2Xm Y (Highly uncommon) case 3: Xf1Xf2 + XmY = Xf2 O+ Xf1Xm Y (Highly uncommon) As it is mentioned that A1 and A3 are present we can say the case 3 is viable option of aneuploidy. Defect in meiosis: Sex-specific differences in meiosis Surveys of cases of human aneuploidy syndromes have shown that most of them are maternally derived. This raises the question: Why is female meiosis more error-prone? The most obvious difference between female oogenesis and male spermatogenesis is the prolonged arrest of oocytes in late stages of prophase I for many years up to several decades. Male gametes on the other hand quickly go through all stages of meiosis I and II. Another important difference between male and female meiosis concerns the frequency of recombination between homologous chromosomes: In the male, almost all chromosome pairs are joined by at least one crossover, while more than 10% of human oocytes contain at least one bivalent without any crossover event. Failures of recombination or inappropriately located crossovers have been well documented as contributors to the occurrence of nondisjunction in humans. source : https://www.wikiwand.com/en/Nondisjunction B) Solution: When the chromosome recombination happens, X chromosome comes from the mother and Y chromosome comes from the father if the born child is a male boy. So, there should not a chance for A3 allele in the son’s cells. That’s the reason for the doctor’s surprise. Please refer to the cases 2,3 in question A. C) Solution: The doctor might be expecting a combination of A1 and A2 alleles in the X chromosomes. Please refer to cases 1, 2, 3. The reason behind this is there can be a defect in meiosis in female and separation of chromatids may not happen. No separation of XmY male chromatids is very rare. The molecular mechanisms include: 1. Central role of the spindle assembly checkpoint 2. Sex-specific differences in meiosis (most common reason for aneuploidy) 3. Age-related loss of cohesin ties D) Solution: When sex chromosomal abnormalities happen (called as aneuploidy), the results can be XO, XXY, XXX, XXXY. In this three cases, the born child will be survivable. Here in our case, the child is a boy. So, the abnormality might be XXY. The boy’s health is relatively normal because he has all the required chromosomes with an additional X from the father. Usually, in these type of situations, one of the X chromosomes in the boy’s DNA will be silent. Or a certain portion of the X’s (say X1 and X2 for the time being. some portions of X1 and some portions of X2) will be silent. It's called X-inactivation. Therefore, in general, the child’s health will be relatively normal. But there are some specific cases where problems do arise. ( out of our scope for now). E) Solution: A Barr body (named after discoverer Murray Barr) is the inactive X chromosome in a female somatic cell. So, in an ideal case we should have 3 barr bodies. For example, men with Klinefelter syndrome (47,XXY karyotype) have a single Barr body, whereas women with a 47,XXX karyotype have two Barr bodies.

Calculus
TutorMe
Question:

Can you please give me a few real-life examples where we use calculus?

Avinash E.
Answer:

One of the most common uses of calculus in our daily life is the PID controller (Proportional-Integral-Derivative Controller).Let me explain in layman terms with very simple and powerful analogies. (For the time being, we will avoid derivations). The reason I am choosing this example is, PID controller is basically an integrator and differentiator which covers most of the calculus. It has a wide range of applications - Coffee Machines. Automatic Air-Conditioners. Cruise Control in Cars. Variable Valve Ignition Time (VVIT) engines for milage optimisation in most of the cars. Water Mixers. Online Advertisements. Industrial control systems, Ships, Missiles, Rockets, UAV etc. PID is a kind of continuous machine learning loop where you need to control the flow of the output without having any prior information of the input (which might be variable and highly volatile) Automatic Air-Conditioner Analogy This is by far the most common use. You set the desired room temperature at 15. Assume that the current room temperature is at 35. The air conditioner will start to cool at a small constant rate first. It then rapidly ramps up the cooling rate in a short period of time. At a certain point of time, the room temperature will overshoot 15 and reach around 12. It then decreases the cooling rate down significantly so that the room temperature can go up. The temperature might overshoot again and reach 16. It increases the cooling again and keeps oscillating around the target temperature till the error gets infinitesimally small. If you change the desired temperature to 20, it will automatically race towards the new temperature and oscillate till the error becomes infinitesimally small again. The best part of a PID Controller is that it will make sure that the temperature goes to the desired point independent of external factors. If you keep a heater in the room, it will work harder to cool the room. Water Mixer Analogy Consider a mixing instrument which is supposed to mix hot and cold water in the right proportion so that the mixture flows out at exactly 35 degrees. This is very easy if you know the exact temperature of the input water flow and other constants like the thickness of the pipe. If you don't know the input temperatures OR if the input temperatures of hot and cold waters are variable and keep changing every hour or every minute, the problem gets complex. Industrial applications face even more volatility. The PID Controller opens the hot valve slightly to measure the change in the output temperature. It will then keep changing it frequently by a constant value. If the desired temperature is far away, it automatically increases the rate of change. So it will first open at x, then 2x, 10x etc till it overshoots the desired temperature and let's say, it reaches 50 degrees. It will then turn the process back and decrease it till it reaches 35. In case it overshoots again to 30, it goes up again oscillating around the target temperature till the error goes infinitesimally small (infinitesimally close to the desired temperature). Online Advertising Analogy You launch an ad campaign on Facebook (Or any site). You target all the UK users in the age group 18 - 22 who are female. You have a spending budget of 200$ per day. There are 100 other advertisers with similar complex targeting criteria with different budgets. Whenever you load a page, the delivery system is supposed to make a decision on which ad to serve. It is at the same time supposed to make sure that budgets of all clients are spent evenly throughout the day. The usage pattern of users throughout the day is unpredictable. It becomes a very complex problem if you consider all the dynamics involved. The controller in the ad delivery system will learn and set a pacing value for every campaign. This is the rate at which that campaign is supposed to be delivered. The pacing is set at a certain value at midnight. Post that it will be adjusted every minute by the PID algorithm so that the delivery for all campaigns remain smooth. If you change your campaign's budget in the afternoon, it will automatically change the delivery pacing to meet the goal. We can go on and on explaining the application of calculus but, will stop here for now.

Electrical Engineering
TutorMe
Question:

Why AC systems are preferred over DC systems?

Avinash E.
Answer:

There are many reasons to support AC systems are preferred over DC systems. A few of them are as shown below: 1. The voltage regulation of AC electricity for transmission systems and distributed systems is less complicated than a DC voltage regulation. A small fluctuation in DC may lead to severe consequences. 2. AC transmission lines are way easier to maintain than DC lines. Plant cost for AC distribution lines (including circuit breakers and transformers) are much lower than the DC transmission and distribution systems. 3. Fault isolation and fault identification in an AC transmission network is easier than DC network. It’s because the sine wave will fall to zero Volt eventually from the fault location making it easier to indentify at some location. 4. Because of the above reasons, the power generation stations are usually AC. So, it will be better to use AC even for household purposes. Otherwise, AC to DC conversion losses will be considerably high.

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