Is the y-chromosome in humans destined to disappear?

I think there are probably few matters that men tend to worry more about than their masculinity. When years ago I saw the announcement of a public talk on “The Disappearance of the y-Chromosome”, I simply needed to hear what that was all about. Since I listened to that talk at that time, a great deal more research data are available on that topic. Fact is that all “maleness” is conferred by the y-chromosome and “femaleness” by the X-chromosome, both being termed “sex chromosomes”. But while women have two X-chromosomes (= XX), men only possess one X and a much smaller y-chromosome about one fourth the size of the X (=yX). Chromosomes (of which all humans have 46  -not counting chromosome number anomalies) occur in identical pairs and that holds true also for the two X-chromosomes in a woman. However, a man’s single y-chromosome’s partner is an X and because of their much different sizes the two chromosomes cannot recombine and repair each other if some bad mutation has occurred on one of them. Think of heaemophilia, which is due to a bad gene on the X-chromosome, but doesn’t make a female ill if she has another “healthy” X. Men do not have that luxury and develop the sickness.

Now assume a bad mutation occurs on the y-chromosome and there is no chance to repair or compensate for it? The only way to weed out the bad gene is to lose it, to delete it and by having to do this repeatedly over millions of years, the y-chromosome is bound to get smaller and smaller. It now contains no more than perhaps 50 genes, while the X-chromosome contains about 20 times that many. According to some researchers, like world famous Australian geneticist Dr Jennifer Ann Graves, about 300 million years ago sex-chromosomes were not yet terribly different from the other chromosomes known as autosomes, but with one of them (the one carrying the gene for maleness) beginning to lose genes, the fateful decline in genes took its course and from about 200 million years ago saw the development of differently sized X and y-chromosomes plus a loss of about 10 genes every one million years. With only 45-50 genes left on present day human y-chromosomes, one can expect the y-chromosome to have disappeared in 4-5 million years. Not so, according to Dr Jenn Hughes, who argues that gene loss affecting the y-chromosome in humans is not constant as only one gene disappeared in the last 25 million years.

However, even she has to admit that ultimately there is the possibility that in many, many millions of years to come, human males (if humans are still around) could be without their little “y”, but not necessarily without the organ many men are usually so worried about. There are, after all, already a few species of mammals, for instance the famed but endangered spiny rats of Amami and Oshima islands in Japan, in which males have no y-chromosome at all. Since the offspring of these rats is not hermaphroditic, but differentiates into male and female individuals (in which the brain of male rats expresses genes to produce hormones that are involved in seminal vesicle protein 5 [Svs5] and cytochrome P450 1B1 [Cyp1b19] syntheses, but the brain of female rats upregulates serine or cysteine peptidase inhibitor and other molecules typical for females), some chromosome other than the “y” must have taken over its function. Yet, what, when, and how exactly that happened is still uncertain.

Virtually all of the few genes still present on the y-chromosome are “maleness”-genes and the SRY-gene is the most important one, as it causes the development of external and internal male genitals. Other genes are involved in regulating sperm and seminal fluid production. How important the y-chromosome is, one can see in cases of people with a multiple X and one single y-chromosome: even XXXy individuals have male genitalia! And one more important aspect of the y-chromosome: because of mutations on it, it allowed researchers to track people’s migration routes out of Africa from 100,000 years ago to now.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content. 

Facilitation, Inhibition and Rebound-Effects

Involved in how cells respond

During the time I worked for my PhD in Neurobiology at the Australian National University 40  years ago under the guidance of Professor G.A. Horridge F.R.S., I really enjoyed electrophysiology. One needed a lot of patience, sophisticated, equipment and a certain amount of skill to successfully penetrate a photoreceptive cell or a neuron in the brain of an insect and to place the tip of an electrode in it to record the cell’s response to a brief flash of light. Of course it depended very much on the species one experimented with and because it was not exactly easy to achieve to get into the cells of the carcass beetle or sawfly larvae that I worked with (and there could be several days when I got no result at all), the moments I did manage to hold a cell long enough to check all kinds of parameters like absolute, spectral and polarization sensitivities, were always “eureka” events and gave me great satisfaction.

The photoreceptive cells of the insect’s retina always responded with a depolarization to a flash of light: a small depolarization if the light was either dim or if it was of a colour that the insect possessed no visual pigment for. However, bigger depolarizations occurred if the stimulating light consisted of a brighter flash or a colour that the insect eye could perceive. I was surprised that sometimes I recorded from cells in which the second flash of the stimulating light gave a larger response than the one that had occurred in response to the preceding (earlier) flash. Of course, this could have been an artefact with the electrode being somewhat better positioned during the second flash. But it could also have been ‘facilitation’, in which the first flash made it easier for the cell to respond the second time it was stimulated. An initial stimulus causing a follow up stimulus to be responded to more promptly, faster, or stronger can physiologically be explained in several ways (involving membrane properties, ion transfers, intracellular cellular messengers, etc.)  For whole organisms one could argue that facilitation means that one organism’s survival can profit from the presence or actions of another organism. A large number of salmon in a small holding tank, for example, will facilitate the spread of fish lice from fish to fish.

Deeper in the insect’s head, further away from the eye towards the brain, some cells I recorded from reacted differently. These cells were producing regular spikes of a specific height that would not change at all even if the stimulus intensity was changed. It was the number of the spikes (i.e. the frequency) that increased in response to a bigger stimulus or decreased when the stimulating light was made dimmer. However, I also came across some cells that totally stopped producing spikes for the duration of the stimulating flash of light hitting the eye. Obviously, the flash of light was inhibiting the cells’ production of neuronal spikes. When the light was off and it became dark again, the train of spikes re-appeared. But not only that: for a short while following the inhibition period, the number of spikes drastically exceeded the normal rate of spikes. It was as if the cell ‘knew’ it had to ‘catch up’ what it had missed during the inhibition period. The effect to compensate for what had been missing during the inhibition period is called the “rebound effect”.

This so-called rebound can of course also be observed in whole animals and is not restricted to cells responding to light.  If, for example, you always sleep for 7 hours and then for whatever reason are forced to only sleep 4 hours one night, you will sleep more than your normal quota the next day. Or, another example, if your dog gets a regular bowl of dog food every evening, but you forget to feed it one day, then the doggie will eat a lot more the day after it had to starve. A response increases when it had paused for a while. Rebound can also mean that symptoms re-emerge after they seemed to have disappeared and this is particularly important (and annoying) when it comes to certain diseases, allergies, etc. However, when after a sad phase in life, happiness returns the rebound effect can be wonderful and does not need a physiological explanation   –  although there is one!

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content. 

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Why are there honey bees on Heligoland

When there shouldn’t really be any?

The small 1.4 km2 large German North Sea rock island of “Heligoland” (in German “Helgoland” and in the local Frisian language “DeatLun”) is a fascinating place. By 1400 the island had been one of the hideouts of the pirate Klaus Störtebeker (meaning “emptying one mug of beer in one gulp”). In 1890 the island was given to Germany from England for the German colony of Zanzibar (which then became British), but before it became British in 1814, Helgoland had been claimed by Danish, Swedish and Dutch rulers. After World War II, when the island (after it had been made into a fortress by Hitler and ‘survived’ attempts by the British 1947 to bomb it into oblivion), it became a famous taxfree haven and tourist resort. I love this unique place and have followed its growth and recovery ever since I had first visited Heligoland in 1955.

When the sun shines and there is no wind (which is rare) this small island can be a magically beautiful place and when in the summer of 2019, I went there with my wife, we were in luck: fantastic weather the whole week. The sun was shining, blue skies, colourful flowers everywhere, bees humming from one inflorescence to the next….But, hey, honey bees? Real honey bees?  There shouldn’t be any, was my immediate thought. It was impossible they could have reached this oceanic island 60 km from the German mainland; bees do not fly across water  – even a small lake is an obstacle for them. I was puzzled. Besides the small area of the island and consequently limited pollen and nectar source would certainly have precluded any bee culture on the island. It annoyed my wife a bit that suddenly I seemed to be more interested in the island’s bees than her (at least until I had solved the puzzle).

The solution was this: successful beekeeping all over the world is associated with conserving the best possible genetic make-up of the queen with target characteristics such as the capacity of honey collection or disease resistance of her and her offspring. For the conservation and improvement of the genetic diversity of the bee, artificial insemination with selected drone bees or having a remote island mating location are the methods of choice. Heligoland is an ideal place to conduct controlled matings to produce honey bee queens with desired characteristics without genetic contamination or mix-up. That is why in one summer season between May and July approximately 80 virgin queens, each with about 600 worker bees, are taken to Heligoland from several locations in northern Germany by ship.

To ensure that high quality drones are present prior to the arrival of the virgin queens, drone hives are placed a fair distance away from the queen mating apiaries. A full frame of drone brood will produce around 700 mature drones, which may live up to 60 days but exhibit declines in fertility after 28 days. It’s been calculated that for 200 virgin queens one needs to have 8 drone mother colonies and for 80 virgin queens one would require perhaps 2,000 high quality drones. A single queen on her nuptial flight (or three or four flights) may mate with several drones and once successfully inseminated queens will be returned to its owner about 3 weeks after the excursion to the honey bee’s “Love Island”. Stray drones (other than the selected high quality ones) can simply not be present there and I learned that annually around 150 virgin queens are taken to Heligoland. One can imagine how happy the bachelor drones must be when the virgin queens arrive! Alas, all drones lose their genitals after mating once and die.

I also learned that not every virgin queen is equally attractive to drones and that queen bees that had already mated with several males were of particular interest to other males. That reminded me of what had been termed the “wedding ring effect” by researchers who had noticed the preference of young human females for men that were married, apparently because such men signified “quality”. But perhaps there was also some competitive element or maybe even ‘envy’ involved. Anyway, I didn’t share this snippet of information with my wife, lest she’d get worried about her husband.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.