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Category: Evolution

SELFISH GENE – selfish to persist

What is a selfish gene? A selfish gene is not a gene that makes an individual selfish. In fact, it may even be involved in the demonstration of a selfless act, a mark of altruism. Selfish gene elements (or selfish DNA) are nucleotide sequences that make copies of itself within the genome. They are regarded as unhelpful as they are of no use since they do not make a protein product. Sometimes, they may even cause harm. However, selfish genes have a vital impact on the survival of the species as a whole.

 

 

 

Selfish gene as a concept in evolution

Richard Dawkin coined the term selfish gene. He also proposed a gene-centric view of evolution in his book “The Selfish Gene”, which he wrote and published in 1976. An excerpt of his book states: “Genes are competing directly with their alleles for survival, since their alleles in the gene pool are rivals for their slot on the chromosomes of future generations. Any gene that behaves in such a way as to increase its own survival chances in the gene pool at the expense of its alleles will, by definition, tautologously, tend to survive. The gene is the basic unit of selfishness.” 1

 

Selfish gene, defined

Selfish gene - illustrated by vix maria
Selfish gene has a vital impact on the survival of the species as a whole. [Illustrator: Vix Maria]

 

Dawkin defined gene as a piece of chromosome that is sufficiently short to live and function long enough. A gene, he delineates, “functions as a significant unit of natural selection”.1 Based on this notion, genes tend to be selfish in a way that they would compete for their survival. They spread by forming replicas that ought to be passed on across generations. And we, as living beings, are only their vessel and an ephemeral vehicle that conveys them to the next vessel.

 

The genes are the immortals…. They are the replicators and we are the survival machines. When we have served our purpose we are cast aside. But genes are denizens of geological time: genes are forever. – Robert Dawkin1

 

Accordingly, a selfish gene would compete for its seat (loci) on the organism’s genome. Those that efficiently make copies of themselves would likely increase in number and survive in the gene pool whereas those that are less effective in the competition would tend to decrease in number.

 

 

Selfish gene and altruism

In spite of its reputation as egoistic, a selfish gene favours altruism, especially, if the act would help its replicas in other members of its species survive. Many animals – from mere ants to the more intricate humans – display altruism, which refers to a set of acts depicting a seemingly selfless behavior for the benefit or well-being of others. Hence, even if the altruistic act would eventually harm an individual, it would still prove beneficial to a selfish gene since more of its replicas in other members could wind up persisting.

 

 

 

Selfish gene elements

Selfish gene elements (sometimes referred to as selfish DNA) are nucleotide sequences that make copies of itself within the genome. They do not necessarily add up to the reproductive success of or confer significant advantage to the organism. Sometimes, they may even cause harm.

 

Recently, researchers have sequenced for the first time two selfish genes from the fungus Neurospora intermedia. A fungal spore that carries the selfish gene known as the “spore killer” would kill the sibling spores lacking the gene. 2

 

Another example of a selfish gene element is that found by the UCLA researchers in a strain of the roundworm Caenorhabditis elegans. They found a pair of selfish genes, one that encodes for a poison and the other that encodes for its antidote. The offspring that does not inherit the gene for the antidote dies while still an embryo because it fails to protect itself from the poison (toxin) produced by the mother. 3

 

 

 

Implications

These studies on selfish genes implicate that there might be many more of them and are probably just hiding in plain sight. Discovering them could one day lead to important uses. For instance, selfish genes could be used as genetic control that would deter the development of pesky parasites at the molecular level.

 

 

— written by Maria Victoria Gonzaga

 

 

 

References:
1 Dawkins, R. (2016). The Selfish Gene: 40th Anniversary edition (4th ed). Oxford University Press. ISBN 0191093076.
2 Uppsala University. (2018, October 15). Unravelling the genetics of fungal fratricide. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2018/10/181015113524.htm
3 University of California – Los Angeles Health Sciences. (2017, May 11). Study of worms reveals ‘selfish genes’ that encode a toxin, and its antidote: Discovery could suggest new ways to stop the spread of disease. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2017/05/170511141937.htm

Evolutionary History of Endemic Gastropod Assemblage in Lake Malawi

Evolutionary evidence showcases the importance of ancient species that evolved through million years ago and still existed at present time. Environmental changes, geographic movement and plate tectonic changes can affect the evolutionary process of a certain species morphologically for survival. The paper signifies the lineage of certain endemic gastropod species in Lake Malawi. The authors try to trace the evolutionary origin of this particular species predicting that this is an endemic species of the certain lake.

 

Evolutionary history of gastropod species in Lake Malawi

Environmental conditions are one of the contributory factors that affect the morphology of the gastropod Lanistes. Two species are said to be endemic of Malawi Lake these are the Lanistes ovum and Lanistes ellipticus.  Phylogenetic analysis shows that these two species did not cluster to any species found at the vicinity of Lake Malawi. The spatial vicinity of the nearby lakes was also examined for the presence of this gastropod, through morphological analysis. And it shows similarity but not genetically using mitochondrial COI gene as a biomarker.

 

Theoretically, a possible potential transition since at Lake Kazuni at around 50 km from Lake Malawi has Lanistes ovum complexes. Fossil record will always admit the origin of the certain species through time. The authors give importance on lineages as basis for taxonomic purposes and evolutionary processes. In which molecular time is relevant in shifting the morphogenetic properties of a certain species.

 

Indeed, Lake Malawi consists of endemic species to the entire Malawi rift rather than endemic to the lake proper.  It also signifies phylogenetic relationship within genus through parallel evolution.  And provides evidence that gastropod Lanistes species are not restricted in certain area but are present throughout Malawi rift.

 

Source: Prepared by Joan Tura from Proceedings Biology Science 

2009 Aug 7; 276(1668): 2837–2846

 

 

 

Why Non-Human Primates Don’t Speak Like Humans

Summary: Why are non-human primates unable to speak like humans? A widely-accepted theory associated it with their lack of vocal anatomy to produce human-like sounds. This was debunked, though, by recent studies upon recognizing vocal muscles similar to ours. It appears that non-human primates are speech-ready and yet do not speak still the way we do.

 

 

 

Perhaps, you have already seen one of those viral videos of pet dogs that seemingly muttered “I wuv (love) you”. Those dogs seemed to make a garbled speech, but still, they unfailingly fascinated people with their apparent “sweet talking“. Thus, one can truly wonder. If these dogs seem to be able to mutter a few, then, how come our closely-related apes and other primates are unable to do so? Even the more evolutionary-distant bird species, such as parakeets, mockingbirds, cockatoos, and other parrots possess the skills to mimic human language and yet our closely-related non-human primates were limited to merely grunts and hoots.

Non-human primates are believed to have no ability to speak or mimic human vocal sounds because of their vocal anatomy. However, a recent study debunked this widely-known theory.

 

 

 

Is it because of the non-human primates’ lack of vocal anatomy?

Why non-human primates are unable to speak has long been blamed on their vocal anatomy. A long-held theory explicates that monkeys and apes are incapable of, at least, imitating human speech sounds because their vocal tract is not that intricately flexible. In a paper published in “Science” in 1969, Philip H. Lieberman and others posited that non-human primates, particularly Rhesus (or macaque) monkeys (Macaca mulatta), were unable to speak like us because of vocal tract limitations. They went as far as to say that the ability for speech as we know it is a “… linguistic endowment …” exclusive to humans.1

A recent study debunked this widely-known theory. In the article, Muscles of the Apes, it referred to the study published in Frontiers in Ecology and Evolution wherein their findings refuted such long-held theory about apes lacking the muscles associated with the vocal communication (as well as bipedalism and facial expressions). These muscles were thought of as exclusive to humans. However, with the availability of more specimens to work on to, they found that certain apes did possess these muscles yet they did not put them to use as humans did. Apparently, the apes were likely speech-ready because they, too, possess the anatomy essential for generating human speech sounds.

 

 

 

Is it because of the non-human primates’ lack of exposure to humans?

Is human language nature- or nurture-driven? We are aware that our language is something that we learned and acquired as we grow. Perhaps, primates would be able to acquire it as well if they could be exposed profoundly to it, thus, came the Project Nim in 1973.

Project Nim was a controversial research. It was a Columbia University psychology experiment on a chimpanzee, named Nim Chimpsky. He was taken as a child from the wild to be raised in a common human household. The research aimed to see if the chimp would be able to acquire human-like behavior and language through nurture. The chimp did learn to convey through sign language but was not successful at speaking even a single word.2

 

 

 

Is it because of the non-human primate’s lack of the necessary brain wiring?

Another theory surfaces to explain why non-human primates are incapable of human speech and it has to do with brain wiring. Accordingly, while non-human primates (particularly, macaques) appear to be well equipped with a speech-ready vocal tract, they do not have the adequate brain wiring that regulates the vocal tract muscles to generate human-like speech sounds. They seem to lack the proper neural control on muscles on their vocal tract and as such are not able to configure them for speech.3

It is also postulated that there might be a molecular predisposition involved, for instance, the FOXP2 (forkhead box protein 2) gene.4 FOXP2 was the first gene identified to play a role in human speech and language development, thus, was called the “language gene“. It is located in chromosome 7 and is expressed in certain cells, including the brain. Mutation of this gene causes speech and language disorder in humans.

Non-human primates do not have the gift for human-like speech because they probably do not need one. Based on recent findings, they have the anatomical features similar to ours yet they produce vocal sounds different from ours. They do have a communication prowess that they use amongst them. It may be far different from ours but it is just as remarkable. Nevertheless, exploring the intricacies of language development could help us learn more about how humans diverged from our non-primate relatives and eventually acquired one of our own.

 

 

— written by Maria Victoria Gonzaga

 

 

 

References:
1 Lieberman, P. H., Klatt, D. H., & Wilson, W. H. (1969). Vocal Tract Limitations on the Vowel Repertoires of Rhesus Monkey and other Nonhuman Primates. Science 164: 1185-1187. Retrieved from
http://www.haskins.yale.edu/Reprints/HL0080.pdf
2 ‘Project Nim’: A Chimp’s Very Human, Very Sad Life. (2011). National Public Radio, Inc. Retrieved from https://www.npr.org/2011/07/20/138467156/project-nim-a-chimps-very-human-very-sad-life
3 Fitch, W. T., de Boer, B., Mathur, N., & Ghazanfar, A. A. (2016). Monkey vocal tracts are speech-ready. ScienceAdvances. Retrieved from http://advances.sciencemag.org/content/2/12/e1600723.full
4 Conger, C. (n.d.).Can chimpanzees learn human language? HowStuffWorks. Retrieved from https://animals.howstuffworks.com/mammals/chimps-learn-language.htm

Prokaryotic Ancestor of Mitochondria: on the hunt

The alphaproteobacteria have been widely cited as the closest relative– and possibly the prokaryotic ancestor — of the powerhouse of the eukaryotic cell, mitochondria. A team of researchers from Uppsala University in Sweden aimed to identify its prokaryotic ancestral origin. However, their recent findings seemed to contradict this notion.1 The mitochondria may have taken an evolutionary fate that is quite different from the one previously thought. Debates on the endosymbiotic theory remain fierce.

 

 

 

Mitochondria, the cell’s powerhouse

The mitochondrion and its small circular chromosome, mitochondrial DNA.
(Credit by Darryl Leja, NHGRI)

 

The mitochondria are best known as the powerhouse of eukaryotic cells. Through cellular respiration, the mitochondrion (single form of the plural, mitochondria) is the organelle responsible for generating and supplying energy (e.g. adenosine triphosphate) needed in various metabolic activities of the cell. It is semi-autonomous as it has its own genome. Referred to as mitochondrial DNA, the genetic material contained in the mitochondrion enables the manufacturing of its own RNAs and proteins. The genome of the mitochondrion is distinct from the nuclear genome and this paved the idea that this organelle is possibly derived from a prokaryote through endosymbiosis (endosymbiotic theory).

 

 

 

Mitochondria and the endosymbiotic theory

An endosymbiosis is a form of symbiosis wherein the endosymbiont lives within the body of its host. In terms of evolution, endosymbiosis was used as a basis of the origin of semi-autonomic organelles, such as mitochondria. Referred to as the Endosymbiotic theory, this theory suggests that mitochondria within the eukaryotic cell came about as a result of early endosymbiosis between prokaryotic endosymbionts and the eukaryotic host cell. The proponents of this theory posited that the mitochondria arose from the prokaryotes (particularly, alphaproteobacteria). One of the proofs raised is based upon the ability of the mitochondria to reproduce via a process similar to the prokaryotic binary fission. Another is the mitochondrial DNA being more akin to the prokaryotic genome (as a single circular DNA) than the nuclear genome.2

 

 

 

Ancestral endosymbiont of the mitochondria

To lay further evidence to the endosymbiotic theory, the research team from Uppsala University in Sweden aimed to uncover the identity of the mitochondrial ancestor. They analyzed large amounts of environmental sequencing data from the Pacific and the Atlantic Ocean and found several species that had not yet been identified. They were able to reconstruct the genomes of over 40 alphaproteobacteria.1 These bacteria include the Rickettsiales group, which is commonly cited as the closest relative among other alphaproteobacteria based on genomic studies 3, and possibly where the mitochondria originated from. Also, the Rickettsiales is a group of parasitic prokaryotes. As such, they depend highly on their host cell to survive. However, the Uppsala University research team was unable to pinpoint the mitochondrial ancestor from their recent analyses on the present-day alphaproteobacteria, including Rickettsiales. And based on what their current data suggest, the evolutionary position of the mitochondria would lie outside of the alphaproteobacteria. This means that this group is not the closest relative, and the ancestor from where the mitochondria evolved could have also given rise to the presently-identified alphaproteobacteria.1

 

 

 

Laying a firm basis for the endosymbiotic theory remains a challenging feat at this time. Nevertheless, we cannot simply rest the case just because the new data said otherwise. Researchers should not be disheartened in finding more decisive and fully comprehensive evidence as to the ancestral origin of the mitochondria. Reaching a consensus may still be far off. However, a disparity in evidence-based viewpoints is better than a clash of unfounded words.

 

 

— written by Maria Victoria Gonzaga

 

 

 

References:
1 Uppsala University. (2018, April 25). “Redefining the origin of the cellular powerhouse”. ScienceDaily. Retrieved from www.sciencedaily.com/releases/2018/04/180425131841.htm
2 “Endosymbiotic theory”. (n.d.). Biology-Online.org. Retrieved from https://biology-online.org/dictionary/Endosymbiotic_theory
3 Andersson, S. G., Zomorodipour, A., Andersson, J. O., Sicheritz-Pontén, T., Alsmark, U. C., Podowski, R. M., Näslund, A. K., Eriksson, A. S., Winkler, H. H., and Kurland, C. G. (1998). “The genome sequence of Rickettsia prowazekii and the origin of mitochondria”. Nature 396 (6707): 133–140. doi:10.1038/24094

Men could go extinct? Y chromosome is slowly disappearing

Hold on to your seats, gentlemen — the male chromosome (Y chromosome) is slowly disappearing at a relatively fast rate and it might be gone completely in the future. This presumption is based on the genetic studies on the Y chromosome. It used to be genetically the same as the X chromosome. However, it has degenerated gradually, and now, it shriveled and became less relevant.

 

 

 

Y chromosome as male-determiner

Y Chromosome and DNA illustration. (Credit: Archaeogenetics, distributed by CC BY-SA 3.0 license)

 

Humans have two types of sex chromosomes: the X chromosome and the Y chromosome. Females have two X chromosomes whereas males have only one. Nonetheless, males have the Y chromosome that is passed on across generations from fathers to sons. In the XX/XY sex-determination system, the Y chromosome is the male-determining sex chromosome. Previously, the X chromosome was regarded as the sex-determiner. This conjecture, however, was eventually proven wrong when the SRY (sex-determining region Y) gene was identified on the male chromosome.1 This gene codes for the testis-determining factor, a protein that triggers testis development. Without this gene, testis fails to develop in males. There are few other genes present on the Y chromosome. However, compared with the X chromosome, the Y chromosome is relatively gene poor and the only highly notable gene on it is the SRY gene.

 

 

 

The disappearing Y chromosome debate

Going back in time, about 166 million years ago, the first mammals had a Y chromosome (called a proto-Y chromosome) that was genetically similar to and of the same size as the X chromosome.2 However, the male chromosome diminished into the short Y chromosome that it is now. The Y chromosome degenerates as it loses genes through time. Unlike the other chromosomes, the Y chromosome does not undergo genetic recombination. Based on the current speed of degeneration, the Y chromosome would likely have 4.6 million years left, which relatively speaking is not that long, considering the 3.5 billion years that life has existed on Earth.2 Some mammals, such as certain rodent species, have already lost their entire Y chromosome. 3 Some experts (referred to as the “leavers”) infer that this event would also happen to humans in the future. This notion was opposed by others (the “remainers”) who believe that the Y chromosome would not disappear completely because it has evolved corrective mechanisms that slow down and deter gene loss. Gene amplification (the acquisition of multiple gene copies) and the presence of palindromes (a sequence that reads the same, whether backward or forward, e.g. AGTGA) help mitigate gene loss.3

 

 

 

Men without Y chromosome in the future

Will men be extinct in the future?

 

If the Y chromosome ultimately disappears in the future, what will happen to men? Will there be men in the future? Experts believe that men will get by when that time comes. Men would still be around just as women have been perfectly fine without the Y chromosome. As for the SRY gene, it could move to a different chromosome. Nonetheless, the chromosome that would take this gene would be at risk of going through the same fate as that of the Y chromosome.3 The absence of SRY gene on the male chromosome is not new, however. In Swyer syndrome, the individual has a Y chromosome lacking the SRY gene and consequently fails to develop testis and other internal male organs. A person with this genetic condition is outwardly female but with a karyotype of a male (i.e. XY karyotype) .2

 

 

 

Further research on the degenerating male chromosome is essential to monitor the rate of gene loss on Y chromosome. One possible implication of the possible complete disappearance of Y chromosome is the impending necessity for more advanced reproductive modalities that can be applied artificially not just on humans but also on other mammals as reproduction by that time would ever hardly become natural.

 

 

 

— written by Maria Victoria Gonzaga

 

 

 

References:
1 “Y chromosome”. (n.d.). Biology-Online.org Dictionary. Retrieved from [https://biology-online.org/dictionary/Y_chromosome].
2 Griffin, D. & Ellis, P. (2018). The Y chromosome is disappearing – so what will happen to men?
Retrieved from https://theconversation.com/the-y-chromosome-is-disappearing-so-what-will-happen-to-men-90125
3 Griffin, D.K. Is the Y chromosome disappearing?—Both sides of the argument. Chromosome Res (2012) 20: 35. https://doi.org/10.1007/s10577-011-9252-1