I would add that most of the bones in the skeleton of the jawed vertebrates (other than cartilaginous fishes) forms as endochondral bone. That means that the bone is formed inside of preexisting cartilage tissue. So if you don't mind classifying cartilage as 'meat' then you could make the argument that meat comes first.

(posted in Genes, Genetics and DNA)

It depends on what you mix them in. If you are just mixing two different types of blood in a vial or a petri dish, then nothing much will happen. If you mix them together inside an organism, however (if you injected lizard blood into a rat, for example), the 'recipient' immune system would probably react to the 'donor' blood which would either kill the recipient or make it very sick.

(posted in Genes, Genetics and DNA)

Introns are spliced out of the transcript before it leaves the nucleus and before translation (protein synthesis) begins. So we consider them 'non-coding' because they are (normally) never seen by the ribosomes and tRNAs. I say "normally" because there can be mutations at the intron/exon borders that can prevent splicing. In this case, the codons within the intron would indeed get translated into amino acids. The resulting protein would be non-functional because all of the amino acids after the mutation would be wrong. Also, many genes exhibit something called "alternative splicing" in which the same gene can be translated into more than one amino acid sequence by being spliced at different locations. For these genes, the splice variant that is expressed depends on things like, the cell type, the developmental period, environmental conditions, etc... In this case, the actual introns still do not get translated, but some sequences that would otherwise be treated as exons do get spliced out.

My guess would be "no". The concentration of sugar in blood is much lower than in, let's say, a grape; so I don't think it would support fermentation. I guess you could make wine with fruit the normal way and then add blood to it, but why would you want to?

Hi Elie,
Our mitochondira are indeed descended from ancient prokaryote ancestors that formed a symbiotic relationship with our eukaryote ancestors and they have the ability to replicate independently inside our cells. So in a sense we are all hybrids of a sort. However, modern eukaryotic cells and their mitochondria are so dependent on one another that one simply could not survive without the other. So it makes more sense to consider them part of the same organism. In other words, your mitochondrial DNA is just as much a part of you as your nuclear DNA. These categories do get tricky though when you mix DNA from different species in situations such as the nuclear transfer procedure you described. Rabbit mitochondrial DNA is different from human DNA (although they must be similar enough that a rabbit mitochondrion can survive and funciton in a cell with a human nucleus and vice-versa). Wo it would not be unreasonable to say that such a hybrid cell is not completely human.

I suppose it depends on your definition of diversity. I would argue that the living synapsids (mammals) are actually more diverse than the living sauropsids. There are mammalian species in pretty much every form including flying (bats), aquatic (cetaceans), arboreal (primates), and so on.

Hi Mairi,
The kinds of mutations you mentioned are called 'point mutations' because they affect only a single nucleotide (or point) on the gene. Point mutations can occur anywhere on a gene so, theoretically, a gene can have as many point mutations as it has nucleotides. However, the number of mutations ina gene is not as important as the type and location. Insertions and deletions usually have a greater impact than substitutions becuase they lead to frame-shift mutations (all of the amino acids down stream of the mutation are either changed or truncated). Substitution mutations have the greatest impact if they occur within the coding part of a gene but genes also have regulatory elements (promoters, etc.) that can be drastically affected by mutations. Also, just for the record, there are other typse of mutations besides point mutations. Inversions, duplications and translocations are chromosomal rearrangements which basically means they are mutations that involve longer sequences of DNA.

Hi Nithya,
When an amino acid is described as polar/nonpoloar or basic/acidic the description only applies to the R group of that amino acid. The amino and carboxyl groups do indeed polarity and acid/base properties to an individual amino acid but when it is incoporated into a protein these groups form the peptide bonds that link the amino acids to each other. The properties of the R groups in a protein are more important for determining the structure and function of a protein.

First of all, not all amphibians have long fingers. Salamander fingers are quite short and caecillians have no fingers at all (or limbs for that matter). Even within frogs, digit length is variable. Having longer hind digits (toes) is likely an adaptation for improved swimming and jumping.

(posted in Mammals)

I'm not sure what you mean by "breathe reflex". Whales, like all mammals including humans, must breathe air and can do so without conscious effort (i.e. reflexively). Whales and other aquatic mammals can hold their breath for much longer than humans which allows them to stay underwater for long periods of time but eventually they must return to the surface to take another breath.

(posted in Fossils)

Hi Jordan,
My first guess is a dog but I am not qualified to say for sure. I suggest that you post more pictures if you still have the skull. A view of the under side would be especially helpful. Also, it is hard to guage the size of the skull so put something in the picture for reference; a ruler or a coin for example.

Meat has a higher density of nutrients than most plants which is what makes it a good food source. The human brain requires a lot of energy to grow and maintain, so the hypothesis you mentinoed suggests that eating meat allowed humans to evlove larger brains because of the increased availibitiy of energy. There are other competing ideas about human brain evolution and the reality is probably that many different factors contributed. It's hard to predict what the evolutionary effect would be if humans went back to a vegan or vegetarian diet. I would not expect much of a change. Modern humans have access to a much better variety and quality of plant-based food than our earlier ancestors did thanks to thousands of years of advances in agriculture.

There could have been some moisture in the mattress before you bought it. If not, then you may just need better ventilation or a way to reduce humidity, in which case you need a HVAC technician and not a biologist.

There are many factors that can prevent members of closely related species from interbreeding. Sometimes it is simple geography: members of the two species are technically able to interbreed but they just never encounter one another. It can also be timing: if two species have different breeding seasons then they will be unlikely to interbreed. Similarly, one species might be nocturnal while the other is diurnal. There are also genetic factors: closely related species can have major differences in their genome including differences in chromosome number. For example, this is what prevents horses and donkeys from interbreeding. A mule is sterile because it has a mismatched set of chromosomes from its parents. Natural selection tends to favor individuals that choose mates from the same species because mating with a member of a different species is less likely to successfully produce fertile offspring and so is usually a waste of time and energy. You and I might have a hard time spotting the difference between a coot and a moorhen, but members of those species can instinctively spot very subtle visual, chemical, or auditory cues that identify other members as potential mates.

(posted in Human Biology and Evolution)

Hi Najwa,
Groups of neuronal cell bodies in the peripheral nervous system are called ganglia. Nervers are bundles of axons in the peripheral nervous sytem that originate (mostly) from the neurons within the ganglia. Axons that don't originate in peripheral ganglia come from the motor neurons in the brain and spinal cord. The sciatic nerve (as well as other nerves) does not contain synapses. Instead, axons within the nerve form synapses with other things in the body such as muscles.

Hi Parsa,
Chemicals like formaldehyde will kill almost anything including healthy human cells. Using formaldehyde to kill HIV would also kill the patient which makes it pretty ineffective as a cure!

Hi Ursula,
Your photo did not come through. Please post again.

Hi Pedram,
You ask a good question, and the answer is a bit complicated. The short answer is that a signal traveling through a neuronal circuit does not know which way to go and does not really choose its path. When a neuron generates an action potential (the electrical signal that carries information along an axon) it travels to all of the synapses that connect that neuron to other neurons. Whether or not a signal is transmitted across a synapse and whether or not the neuron on the other end of the synapse responds depends on the "strength" of the synapse. Synaptic strength depends on a lot of factors that are too complicated to go into here (the Wikipedia page on synapses is a good place to start if you want more details). The bottom line is that, for something like the auditory pathway which includes all of the connections betwen the hair cells of the innear ear and the auditory cortex, all of the neurons involved are connected by synapses with a high synaptic strength. Meanwhile, pathways that might take the signal to the wrong part of the brain (the visual cortex for example) are either not connected by synapses at all or have connections with very low synaptic strength.

Hi Went,
Coelocanths, like other bony fish, have a rigid flap covering their gill opening called an operculum. This prevents water from flowing backwards through the gills which allows them to use their mouth like a pump to push water over their gills even when they are not actively swimming.

Hi Carrie,
Most mammalian embryos start out with either two X chromosomes or one X chromosome and one Y chromosome. This is because each embryo gets half of its chromosomes from each parent. A female embryo will inherit one X chromosome from its mother and one X chromosome from its father. A male embryo gets one X chromosome from its mother and one Y chromosome from its father. A gene on the Y chromosome causes the embryo to develop into a male. There are rare cases where the gene (called SRY) malfunctions and the embryo develops female sexual characteristics despite carrying a Y chromosome. That is why some people say that female is the "default" gender for mammalian embryos.
As for birds, they do have ZW sex chromosomes instead of the XY system of mammals. However, the mechanism for sex determination is not as well studied as it is in birds so it's not clear if it's the presence of the W chromosome that triggers female development or the presence of two Z chromosomes that leads to male development.

Hi Michael,
The reason that curry and other spicy foods leave a burning sensation when you're eating them and sometimes when they are leaving is that the capsaicin receptor (the Trpv1 channel that David mentioned) is found in the epithelial tissue at both ends of the digetive system. Capsaicin is broken down by stomach acid but if you eat a lot of spicy food in one meal, some capsaicin is going to make it through and activate those receptors on their way out.

Hi Anna,
It looks like the caterpillar of some kind of bagworm moth, although they are usually bigger and found outdoors. That's my best guess.

This is a phenomenon called parthenogenesis. It has been observed in many animals including some snakes. You can read more about it here: http://en.wikipedia.org/wiki/Parthenogenesis.
Usually when this happens, the female produces an egg that develops into an embryo without being fertilized by sperm. Because the embryo does not possess any chromosomes from a male parent, it will usually be a genetic clone of the mother.

(posted in Fossils)

Hi Brian,
I don't think that is an actual fish fossil. It is probably a digitally created geometric pattern that happens to resemble a fish skeleton.

Hi Eva,
The closest living relatives to brachiosaurus (as well as all the other dinosaurs) are modern birds.

Try a mixing a cup full of apple cider vinegar with a few drops of liquid dish soap. Set it out uncovered near the place where you see the flies. They should fall into the liquid and drown.

That is almost certainly a rotifer. They are very common animals in ponds and streams. They are in a phylum all their own and are more closely related to things like flatworms than they are to insects.

Hi Krai,
The question of how much the two hemispheres of the brain contribute to a given task (also known as lateralization) depends a lot on what function you are talking about and what part of the brain you are talking about. First, when you refer to the two brain hemispheres, you are probably referring to the two halves of the cerebral cortex and some of the underlying structures. The rest of the brain (usually referred to the brainstem) is not very lateralized for most functions. For some of the sensory systems, the cerebral cortex is very lateralized and usually crossed. Sensations of touch from the left side of the body are processed by the right side of the brain and vice versa for example. The same is true of the parts of the brain that control the body muscles. Some sensation is processed bilaterally though; sounds from either side of the body are processed by both sides of the brain for example. Some higher level functions are laterlized also. Language is the best example: for most people language production and comprehension both occur in the left cerebral cortex only. As far as I know, emotional responses like fear (the example you asked about) are processed bilaterally, meaning that both sides of the brain contribute equally. However, there could be subtle differences between the two sides for these kinds of functions that could only be elucidated from very careful experiments.

(posted in Fishes (Including Sharks))

Hi Evan,
As you suggested, bony fishes do have multiple gill slits, but they are covered by an operculum. So your real question is "why did the elasmobranchs (sharks and rays) lose their operculum". I'm not sure if anyone knows the real answer, but it could have something to do with the transition from a bony skeleton to a cartilaginous skeleton. Perhaps an operculum made of flexible cartilage just would not be as effective as one made of rigid bone. Another possibility is that the operculum had to be lost in elasmobranchs because of their unique jaw structure. I'll admit that I'm not a fish expert, so someone else with more knowledge might have some better ideas.

Hi Jagger,
It's hard to tell much from your picture. It might help if you told us where you took the picture.

Hi Timothy,
I think it is some kind of roach; probably a juvenile.

The first picture does not look like any kind of embryo that I have ever seen, but if it is, my first guess would actually be a bird with the tail and hindlimbs missing. As for the second picture, my guess is a dog based on the shape of the face and forelimbs.

(posted in Genes, Genetics and DNA)

Hi Sara,
The normal gestation period for cats is a little over two months, so if the mother cat has not been out of the house in five months, then you are probably looking at a case of inbreeding. The good news is that inbreeding by itself does not cause health problems in offspring. The problem with inbreeding is that two closely related cats are more likely to be carriers for the same recessive genetic traits than two cats that are not closely related. Therefore, inbred cats are more likely to have genetic diseases or other rare genetic traits than outbred cats. It looks like four kittens is a normal litter size, but the stillborn kitten could have been the result of a genetic disease. Your veterinarian can do a genetic test to determine whether or not your male cat is the father of the kittens. She could also do genetic testing to determine if the kittens have certain genetic diseases. These tests can be expensive though and if they do not show any symptoms of disease, then there is probably not much to worry about. My suggestion is to have all of your pets spayed or neutered to prevent this from happening again.

(posted in Mammals)

Hi Fabio,
My best guess is that dogs and cats have to drink by lapping instead of sipping because of the shape of their jaws and the fact that they don't have cheeks. Dogs and cats and other carnivores have jaws that evolved to be able to catch moving prey which means they need to be able to open their mouths as wide as possible. Cheeks, which are necessary for sucking, get in the way if you need a large bite profile.

(posted in Human Biology and Evolution)

Hi Tottionna,
The short answer is 'yes': you brain can store many memories that are difficult or impossible to bring to concious recollection (remember). The reason for this can have to do with the nature of the memory such as how long ago the memory was initially stored, what other memories it is connected to, etc. Memory recollection can also be impaired by damage to the brain or due to conditions such as Alzheimer's Disease.

Hi Ali,
I'm not sure I understand your question. Humans have always reproduced sexually as did our ancestors. In fact, sexual reproduction has been around for more than 500 million years. So it does not make sense to ask when human sexual reproduction "began". If that does not answer your question, please feel free to post another.

Chromosome duplications and deletions occur as a result of crossover errors between homologous chromosomes. This can only happen during the first prophase of meiosis because this the only time that homologous chromosome pairs line up to form crossovers.

My guess is: probaby not. Hair is a pretty good insulator so, if anything, a beard would actually cause blood going to the brain to be warmer by preventing heat from escaping from the neck but the effect is probably negligible. Your skin temperature can vary quite a bit from place to place for a lot of reasons such as the amount of blood flow to the region, the amount of subcutaneous fat, etc. but your body temperature below your skin is mostly uniform throughout your body. That is why checking someone's skin temperature is not a good way to tell if they have a fever. Therefore, any heat gained or lost from the skin of the neck would be distributed around the body and would not have any specific impact on the brain.

Hi May,

To answer the first part of your first question: for most genes, both the maternal and paternal copies are used for protein synthesis. There are important exceptions to this such as X chromosome inactivation and DNA methylation but those are pretty complicated subjects for this space.

The answer to the second part of your fist question ("wouldn't two different chromosomes make slightly different genes?") is 'sometimes'. Different versions of a gene are called alleles. If you inherit two different alleles for a gene from your parents, you are called heterozygous for that gene. When the two alleles are the same, you are homozygous. Whether you are homozygous or heterozygous for a gene, both alleles can be expressed at the same time even if they code for slightly different proteins.

On to quetion two: in the early days of genetics, it was believed that each gene was responsible for the expression of one trait and that each trait was the result of the action of one gene. This is the one-to-one model that you mentioned. This model is still taught to beginner biology students because it is easy to understand. The reality is that many genes (probably all) influence multiple traits and that many traits (probably all) are the result of the expression and interaction of multiple genes.

Hi Lina,
A clone, be definition, is an exact genetic copy of the individual it was cloned from. So, a clone will always be the same gender as its 'parent'.

(posted in General Biology)

Hi Sarah,
Animals are multicellular by definition. All animals develop from a single cell (the zygote) and there are some animals that can reproduce or regenerate from a single cell, but they still must spend at least part of their life cycle in a multicellular state. All cells have a cell membrane so that would not be defining feature of animal cells. Some organisms have cells with an extra layer called a cell wall, but animal cells do not posess this feature.

(posted in Evolution)

That's a good question Thuong and I'm not sure anyone really knows the answer, but we can make some guesses. Like you said, chloroplasts are a great way to convert energy from the sun into chemical energy but they have their limits. For one thing, they only work where sunlight is plentiful and for many parts of the world (the deep oceans, the poles, etc.) that is not the case. When photosynthesis is not occuring, chloroplasts are actually a liability because they require a net consumption of energy to maintain. Another problem is that independent movement (a hallmark characteristic of the animal kingdom) requires a tremendous amount of energy and photosynthesis simply cannot convert enough energy for the kind of sustained locomotion that animals are capable of. Animals, therefore have evolved the ability to get their energy from other organisms either by eating plants or other animals or by acting as parasites.

It sounds like you are asking about lice:

I am not a forensics expert, but some of the bones look like they have been cut into pieces rather cleanly. My guess would be that they are from a butchered cow or pig.

One point of clarification: the corpus callosum only connects the left and right cerebral cortex. Other lateralized parts of the brain are connected by other pathways such as the anterior and posterior commisures for example. Apparently a true corpus callosum is only found in placental mammals so it is a relatively recent addition in evolutionary terms. It probably evolved as a shortcut for communication between the left and right cortices. As the cerbral cortex became larger during mammalian evolution, the distance between neurons on the two sides became greater. The corpus callosum would have been advantageous because it would have allowed for shorter axons connecting the two cerebral hemispheres.

Currently, the technolgy to create the kinds of genetic modifications you are talking about are not possible. Also, even if the technolgoy existed, the ethical implications of genetic modification of an otherwise healthy individual to improve natural abilities are questionable at best.
But let's set that aside for the time being. A change in the binding kinetics of retial and opsin probably would not affect the sensitivity of the photoreceptors very much. If anything, you would want to slow down the rate of binding so that the receptor would remain active longer. Even then, however, other steps in the phototransduction process would prove rate-limiting. Increasing the number of rods would help, but you really would want to change the distribution of rods because in the normal eye, the center of your visual field is dominated by cones and the rods are more abundant found in the peripheral retina. Increasing the level of rhodopsin would also increase sensitiviy but again you would need to solve the problem of having the center of your visual field dominated by cones.

I can't find a reference either way, but as far as I know fish do not have an epiglottis per se. Instead, most fish that have lungs (which includes lots of kinds of fish other than lungfish) or a swim bladder that is connected to the esophagus have a ring of circular muscle that can constrict the airway and prevent food or water from getting into the lungs. Of course, fish without lungs or with a swim bladder that is not connected to the esophagus would have no need for an epiglottis.

It is possible that the birds are seeing their own reflection in the glass. Many animals, when presented with a mirror, are unable to comprehend that they are seeing themselves in the reflection and instead assume that the reflection is another individual. The pecking may be some kind of territorial display or other social behavior.

Here is another one that is a little bit closer to the one you found: http://www.scielo.br/scielo.php?pid=S16 … ci_arttext

I believe the smaller ants ride on the leaf pieces in order to protect the leaf and the worker that is carrying it from flies and other parasites or attackers.