Take the 2-minute tour ×
Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. It's 100% free, no registration required.

I know that species have been classified on basis of reproduction , DNA similarity , niche, etc.

Has there been a classification based on locus of genes ? What are the drawbacks/shortcomings of classifying this way ?

Isn't it simple to classify on this basis as - a species can have variation at a locus but the position of that locus with respect to a chromosome is fixed in every individual of that species. This fact can eliminate the subjective criteria of DNA similarity.

But I think this isn't valid for bacteria as there is so much recombination going on.

share|improve this question
3  
The position of gene is not always fixed within a species. There are Copy Number Variant within species for examples. A great part of the variation within humans is due to CNV. I agree that it is important to consider other genetic variations than only the alleles. CNV, position of genes, regulatory sequences and other stuff are important too. The concept of species is a poor concept which is old as Aristotle and important in the christian culture but we have to accept that this concept is not a natural category. You won't find the perfect objective definition of what is a species. –  Remi.b Dec 8 '13 at 10:19
    
@Remi.b Yes , but are CNVs genes ? Are there variation in no. of genes in population ? –  biogirl Dec 8 '13 at 15:15
1  
CNV's are DNA sequences of any length that are present at several different number of copies along individual in a population or along species. THese sequences can contain one or several genes. So the answer to your question is yes! There are variation in number of genes within a species. Here are two references that might interest you: adsabs.harvard.edu/abs/2006Natur.444..444R and genome.cshlp.org/content/16/8/949. You will as well find some information about CNV on the [wikipedia page] especially under "identification". (en.wikipedia.org/wiki/Copy-number_variation) –  Remi.b Dec 8 '13 at 15:26
    
@remi.b Alright.Thanks! –  biogirl Dec 8 '13 at 18:29
    
@Remi.b Hello! I think you have answered my question in the comments. Would you like to write an "answer" ? –  biogirl Apr 29 at 15:40

3 Answers 3

up vote 5 down vote accepted

The position of a gene is not always fixed neither within nor between species. There are Copy Number Variation for example. A great part of the variation within humans is due to CNV. I agree that it is important to consider other genetic variations than only the alleles though. CNV, position of genes, regulatory sequences and other stuff are important too in the description and the functionality of a lineage.

The concept of species is a poor concept which is old as Aristotle and important in the christian culture but we have to accept that this concept is not a natural category. For french speaker people this podcast(Follow: Biodiversité: Plus qu'une simple histoire de conservation/Pierre-Henry Gouyon) is of interest. You won't find the perfect objective definition of what is a species. Here and here are posts that discuss the definition of species.

share|improve this answer

As Remi points out you are generally incorrect but the locality idea is specifically ok. The positions and types of mutations and divergence for specialization in certain genes regardless of their place in the genome is key in determining homology which is used for species determination at the molecular level. The drawback is: its rather expensive when most species differences are obvious at the phenotypic level.

share|improve this answer

I would add:

Most categories in sciencie (species, order, living, planets, moons, stars, organs, fruits, etc.) are not "real". We (humans) create categories and attach objets to them in order to make general assumptions, so we can say things like "Most objects of category X have Y property."

Then, the way we define categories it's mainly the most practical way. And sometimes we addapt definitions, when there are practical motivations.

I think the motivation to define species related to the usual intra reproduction hability (and usual inter reproduction inhability) it's because that mantains certain homogeinity. Maybe a better definition would be something like "two groups of individuals belongs to the same specie if the rate of fertility among their individuals is > x %".

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.