Hot answers tagged

17

Human female cells contain most of the genetic information required to make a male, but they do not contain a critical component: The Y chromosome. This is a relatively small chromosome. Wikipedia claims we have identified around 200 genes on it to date, compared to estimates of 20,000 - 25,000 genes overall in the human genome. Importantly for your ...


13

It has mainly to do with the embryonic origin of organs, with the heart being a typically left sided organ, it develops sharing some nerves with the left thorax and left arm. There is however high variability, typically among patients but also among coronary vessels. For instance, right coronary stenosis may lead to abdominal pain, whereas left circumflex ...


10

Generally, cold suppresses sweetness. As an example, consider soft drinks that are usually served cold: they taste sweeter when warm (like you said with your examples of drinks). Our taste receptors send a stronger signal to the brain when activated by warmer substances and so the perception of sweetness, in this case, is lessened when we consume cold food ...


5

I rather would say that the lack of North/South Symmetry in pigmentation is that we forget how quickly human beings have spread. In prehistory, people have come to populate every continent over perhaps the last 60,000 years. While in that time its clear that several mutations have popped up to influence skin color, they are pretty rare compared to the ...


5

There are only 26 letters in the English language, and more than 80% of words are under 10 letters. Yet there are over a million English words. Nonsense words don't count. Now imagine the possibilities of a 20 letter alphabet, where the average "word" length is about 375 letters, and where words of up to 800 letters are possible. And that also does not ...


5

This is not an area I know well, but I'm familiar with a couple of studies that have tried to estimate the heritable (genetic) component of homosexuality in humans. A review paper by Rice et al (2012) points out that: Pedigree and twin studies indicate that homosexuality has substantial heritability in both sexes, yet concordance between identical twins ...


5

Our pain-sensing neurons work in useful ways only when they inform about skin areas or muscles. When nettles sting your left hand, you want to retract your left hand right away. This is in part an educated reaction, because your brain ca re-learn what sensing neuron corresponds to what side of you hand when surgeons stitch together broken nerves. With ...


3

The Wikipedia page you linked says that sweat is composed of a liquid similar to blood plasma. As all DNA in humans is stored in the nucleus of a cell, it seems unlikely that the sweat itself would contain any DNA. However, when someone sweats significantly, I can't imagine that no skin cells end up in the sweat. In any case in which this occurs, then the ...


3

I think the reason is primarily, that it is more quiet (the chance is very low that other people are disturbing your sleep) in the night as well as it is also dark. Keeping in mind, that the brain "gets tired" due to some proteins (melatonin) and in contrast, being more awake during the day, it seems to be just logical that the sleep in the night is ...


3

But why does this mantra persist; where does it come from? Behind this line of inquiry is a fascinating observation about the disconnect between the laboratory and the clinic. The basic answer, from my perspective, goes like this: It is doctors who talk with people about their urine, and any testing thereof; for doctors, urine is practically1 ...


2

I found this research paper (pdf) by D. Roger Illingworth, William S. Harris, and William E. Connor (Journal of the American Heart Association, 1984) that offers some help. Its abstract says: Diets rich in omega-3 fatty acids derived from fish oils lower the plasma concentrations of low density lipoproteins (LDL) and very low density lipoproteins in ...


2

Some people do die from graft vs host disease after bone marrow transplants involving ABO incompatibility, but not usually from blood clots. Foreign red blood cells don't usually form significant clumps (or clots) as a result of an antibody interacting with a surface cell antigen. They can form tiny clumps, however, that are not life threatening, but simply ...


2

We don't get it from the sun, it's synthesized. Humans can get it... via nutrition. via synthesis in the skin, which depends on UV radiation. Sun is the major source of it (the radiation, not the vitamin), and synthesis in the skin the major source of the vitamin. However, it needs further modification in the liver or kidney to become bioactive. UV ...


2

A couple of quick google searches would tell you that the important part of sleep is the REM (Rapid Eye Movement) sleep. REM stands for rapid eye movement. During REM sleep, your eyes move quickly in different directions. That doesn't happen during non-REM sleep. Usually, REM sleep happens 90 minutes after you fall asleep. The first period of REM typically ...


2

You don't get energy from breaking chemical bonds, you only get energy from making chemical bonds, while breaking chemical bonds requires the input of energy. However, in practice chemical bonds are always broken as others are formed, and the net number of bonds is generally constant. Otherwise you would end up with free radicals, which are highly reactive ...


2

I am no expert in this but I had asked my doctor the same question the last time I fell sick and I'll try to paraphrase his explanation. "There is this protective lining on our respiratory tract called "Respiratory Mucosa" that acts as the first line of defense against pathogens. But when you consume cold food and beverages , this membrane gets congested or ...


2

My previous answer was to the original question which focused on red blood cells which do not contain DNA. Now the question has been revised to focus on tissue transplantation, where the cells do contain foreign DNA, my amended answer deals with a couple of the points raised, but only briefly with the question of identification. Incorporation of foreign DNA ...


1

I believe what you're describing is referred to as ectogenesis which is essentially developing a fertilized egg inside an artificial womb until it’s able to survive outside the controlled environment. So is this possible outside of science fiction? To answer this we have to compare the stages of human reproduction and how close today's science and technology ...


1

I found an article (1) which may help you understand what happened on your tongue: Light cooling from 37 to 21°C of beverages increases your sweet taste adaption, but not actual sweetness of your drink! Another article (2) states, that a certain receptor for sweet taste perception is heat-activated. So I guess there is no universal rule for any drink, you ...


1

Adding to @David's answer, there has been some recent work looking at Neanderthal DNA in the context of Denisovan and modern human populations. David Reich's group [Sankararaman et al. Nature 2014] found Neanderthal-derived alleles in genes that affect skin and hair (specifically keratin filaments), as well as some that confer risk of disease. Another cool ...


1

There was a very readable piece on this topic by Chris Stringer in Nature in 2012. At that time his general conclusion was: It is not yet clear whether the archaic DNA many of us carry is tied to any visible traits. Although he added: More controversially, some of the known differences in coding DNA between Neanderthals and recent humans are ...


1

Similarities Despite major overall differences, there are some basic similarities in the two processes: Light energy excites an electron to a higher energy level. A covalent bond is broken as the electron moves elsewhere. This process is called ‘photolysis’ and is purely chemical. Differences The difference is in what happens to the excited electron ...


1

The stomach linings generally secrete gastric acid (HCl, KCl and NaCl) and the native pH of the stomach is around 2. The longer you fast, gastric acid levels keep increasing until it reaches around 1-1.5. The food that you eat increases the pH levels of your stomach because the acid reacts with the food while digestion. Depending upon the type of food you ...


1

In addition to @alec_djinn's answer, viruses can also indirectly be toxic by causing lysis in cells that themselves have toxic components. The presence of bacterial endotoxins in poorly filtered solutions of early attempts at phage therapy is probably the canonical example of this.


1

I did research on whether or not silica gel was poisonous, because I wanted to use a bunch of the silica gel beads as an abrasive method to clean out a bottle that was dirty. I added a bunch of silica gel beads and a bit of water into the dirty bottle to be cleaned, I put the lid back on and tilted the bottle back and forth and used the beads as a way of ...



Only top voted, non community-wiki answers of a minimum length are eligible