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As we know, a change in allelic frequency leads to evolution, and as these changes accumulate a new species is created.

My question has two parts -

  1. A classical definition of species which is now not accepted everywhere: Two different species are the populations that has lost the ability to interbreed among themselves to produce viable offspring. I have read some of the answers on stack exchange addressing the genetic reasons for hybrid sterility. They frame faulty pairing in meiosis as the main reason, but if the genes are on the same loci in two different closely related species how does a change in allelic frequency lead to faulty meiotic pairing in the germ cells of the hybrid?

  2. In the divergence of two populations sharing a common ancestor, allelic frequencies are changing, but at what point are the populations called two different species?

acvill
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Samardeep singh
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    Does this answer your question? How is genetic speciation defined? To quote one of those answers: "It turned out that the main differences between the two genomes were clustered around regions where chromosomes were rearranged. Although indicative of the cause of speciation, it can nonetheless also be the result of it. We can never be sure." Chromosome rearrangements are of course one of the most obvious mechanisms for bad meiotic pairing and non-disjunction. – Maximilian Press Jul 07 '21 at 19:30
  • what do you mean by chromosome rearrangement can you define and elaborate the process by which it happens? – Samardeep singh Jul 07 '21 at 19:38
  • ok this answers the 2 nd part of my question that when can we say two population are no longer the same species (:In other words, when two suspected sub-species are not able to produce viable offspring, they can be considered to be two species." but i was looking into the biochemical or genetic reason and their relation with changes in allelic frequency, though its a good answer. – Samardeep singh Jul 07 '21 at 22:28
  • Chromosome rearrangement: when structure of chromosomes changes. This is a very large and complex field of inquiry, and there are many mechanisms by which it happens. That is a large question in itself, I recommend doing background research and possibly asking a separate question if the term is unfamiliar. 2. Biochemical/genetic reason for speciation: I think that the take-home message is the one in the linked answer, which is that there is no single mechanism by which species are defined. I would consult the linked answer for more information about how species are defined.
    • – Maximilian Press Jul 07 '21 at 22:41
  • Directly to your interest in allele frequencies: I don't think that changes in allele frequencies are going to tell you much about speciation. I think that they are an inexact and rather generic description of an extremely complex and context-specific process. – Maximilian Press Jul 07 '21 at 22:57
  • Please take the [tour] and then consult the [help] starting with [ask] questions effectively on this site. From this you will see that we expect questions to be focused (including one question per post), well-researched (in particular, you need to look for overlapping questions on this site), and clear. — In one sentence you wrote "if the genes are on the same loci", which doesn't seem to mean anything, and "how does a change in allelic frequency lead to faulty meiotic pairing", which assumes something that isn't true. I strongly encourage you to do some background reading/research. ... – tyersome Jul 08 '21 at 05:49
  • ... I have found Khan Academy to be very helpful for learning the basics of a subject. You can then move on to Understanding Evolution from the University of California, Berkeley. After that there are many free textbooks available at the NCBI Bookshelf and many other online resources. – tyersome Jul 08 '21 at 05:52