A tetrad is a set of four interrelated elements.
The notion of tetrad refers to a series of four elements that are related to each other . It is a group of four components that maintain a link.
Some examples
Although its meaning is easy to understand, its use is not common in popular language. For this reason, we present three examples to see the term in context and facilitate its understanding: “The ease of contagion, the lack of a vaccine , the absence of specific treatments and the lack of responsibility of many people constitute a worrying tetrad for doctors. facing COVID-19 around the world” , “The writer told the story of the detective in a tetrad of novels that must be read as a unit” , “A tetrad of melodies plays throughout the film and is repeated over and over again."
The first example tells us about a set of four elements that are fundamental for health professionals who are in the midst of the fight against the coronavirus pandemic , which took place at the beginning of 2020 and affected all aspects of the patient's life. entire planet. The term tetrad is used because the bond that exists between them is unbreakable, they are united from any perspective and the situation cannot be analyzed leaving one of them aside. Similarly, trying to solve just one of them is not feasible, since balance would be achieved only by attacking them all simultaneously and gradually.
We continue with a different sentence, in which the concept of tetrad helps us relate four literary works: it is a series of novels that make up a great story , which is why it is necessary to read them all to understand the entire plot and appreciate all the nuances that the author printed in his characters and settings. Finally, the four melodies mentioned in the third example were not composed in an isolated and independent manner, but rather are related to each other and serve to weave the story together sonically.
Four lunar eclipses
In the field of astronomy , the idea of tetrad is used to refer to a succession of four total lunar eclipses that occurs in a period of a few months . The phenomenon is usually associated, in popular beliefs, with the imminence of a great tragedy .
There are those who find supposed allusions to tetrads in the Bible . Links are also established between tetrads and major historical events, such as the tetrad of 1493 and the expulsion of the Jewish community from Castile and Aragon or the tetrad of 1949 and the Six Day War .
In this framework, there is also talk of Blood Moons , always with the idea of total eclipses that are not interspersed by other partial ones, and that take place in periods of six months. Its link to religion and tragedies is fascinating, like any other theory that cannot be completely proven or disproved. Returning to their name, they are called "blood" because of the color they acquire during the eclipse, which is usually reddish or orange, and this occurs due to the dispersion of light at the time they occur, whether it is sunset or the dawn
Four uninterrupted total lunar eclipses represent a tetrad.
Four chromatids
In the field of biology , on the other hand, the concept of tetrad appears. In this case, the set of four chromatids that, in the first division of meiosis, are found in synapses , is called a tetrad.
The tetrad arises when two homologous chromosomes, in prophase I of meiosis , replicate and pair. In this way the tetrad is made up of four chromatids, two for each chromosome.