Hi,
my question is, can you predict by examining the DNA of two "species" if they can breed or not? I guess it has something to do with the number and size of chromosomes, is that correct? There must be other factors as well I think.
Not sure what you're trying to ask here.
Species cannot interbreed and produce fertile offspring.
If you're asking if you can examine the DNA of two individuals of the same species and determine if they can breed, not really. You would need a number of functional tests to determine whether each of the individuals is fertile.
Short answer no, or at least I don't think so. The genomics of speciation is an up and coming field of research, but one which is not fully characterised as yet.
The number and size of chromosomes is an easy place to start, however while chromosome number disparity means hybridisation is unlikely, it may not be impossible, and First generation sterile offspring are produced in a number of chromosome mismatched hybridisations. For plants, even this is not much of a barrier.
However even if the number of chromosomes appeared to match perfectly, without a full genome sequence you don't know what genes they are carrying (or whether there have been any gene translocation events, chromosomal inversions that prevent genes aligning etc). Producing a whole genome sequence is no easy task, and most organisms are still unsequenced. Even if you have a full genome, the function of each gene will likely be unknown without characterisation studies. At this point you will have no idea whicg genes may be important to reproduction.
Barriers to hybridisation can pop up at any point along the route towards reproduction and while the ultimate cause of these is usually genetic they can work at different stages, animals not recognising each other as mates, genitals which do not fit together, changes to the chemical cues such that sperm do not recognise egg or vice versa.
Speciation is a fascinating area of research by looking at partially fertile hybridisations we can look at speciation in action, but at the moment we are very much at the stage of trying to understand how barriers to hybridisation occur and what they might look like at the genetic level, only when we understand these processes can we start to make accurate predictions
Firstly, it's probably worth pointing out that you can't really just look at the DNA of two individuals. The number of species for which we have complete, assembled genomes is tiny, and each new assembly costs too much money for people to do it just for the sake of curiosity (more's the pity...)
Supposing that we did have the entire DNA sequence of two individuals, and a reference sequence that told us about normal sources of variation (so e.g. saying 'yes parent A and parent B have different bases at position 297 of gene XYZ, but so do lots of individuals' as opposed to 'all of the individuals like parent A have T and all of the individuals like parent B have G, so maybe that's an important functional base') then we still couldn't conclusively say that two individuals could breed.
It's possible to spot a number of scenarios where they couldn't breed because of molecular barriers: Phil has mentioned the chromosome number issue. Humans have 23 pairs of chromosomes; chimps have 24. Therefore we'd never be able to produce fertile offspring, because they would have 47 chromosomes.
There is also a system called the Mismatch Repair system that, amongst other things, spots similar-but-not-close-enough sequences during crossing over (the process that mixes up your parents genes when you produce gametes) and shuts down the process if they try to recombine.
But like many things there is a lot of variation between species. For instance polyploids have to keep their own genomes separate from one another (so that their 'A' genomes don't recombine with their 'B' genomes) so they have more stringent conditions for what they can and cannot breed with than some diploid species.
I would like to add just because it is often not known that plants are far more relaxed about this topic than animals. And I think I cannot give you now a real good answer why and if and where is the limit but just at the side, there exists a small army of excellent scientists in free institutes and breeding companies just working on this question and mainly trying to break the intercrossing barriers. In case for solanaceous species, potato can interbreed with a huge number of wild potato species and their relatives with different ploidy levels. As it seems the only important factor is that the ploidy is even. On the other hand it cannot interbreed with tomato which on a genetical level is very similar to potato (sometimes more similar than these wild potatoes). And one should just imagine how nice it would be to have a pomato. One can eat the berries in a bolognese sauce and the tubers in the gnocchi.
Last edited by Gabor Gyetvai (9th Sep 2012 21:07:34)
Experts: login to post a reply
Dave Warburton
Alistair McGowan
Graeme Lloyd
