Talk:Chromosomal crossover

Disambiguation

Someone needs to disambiguate this. KirbyMeister 01:36, 10 May 2004 (UTC)

F. A. Jannsens

The Idea of crossing over was first proposed by F.A. Janssens. Does anybody know anything more about him? Fawcett5 18:17, 17 January 2006 (UTC)

Yes, that needs to be changed. The cytological basis of crossing over (and even the term "crossing-over") was first described by F.A. Janssens. TH Morgan just used that knowledge to help him expain gene linkage. Morgan postulated that the crossing over (that Janssens had already discovered) created new chromosomal types in a few gametes. — Preceding unsigned comment added by 132.170.160.178 (talk • contribs) 23:32, 27 January 2007 (UTC)

Merge Proposal

This article should probably be merged with / redirect to genetic recombination. Gringer 03:02, 7 July 2006 (UTC)

• Sorry, after reading Genetic recombination, it makes sense to keep this. The pictures, at least, should be changed to reflect the breakage and rejoining mentioned in the first paragraph, rather than physical twisting of chromosomes. --Gringer 03:12, 7 July 2006 (UTC)

significance of crossing over

what is its significance can naybody tell me please —The preceding unsigned comment was added by 203.101.182.58 (talk) 11:28, 27 February 2007 (UTC).

Requested move

Chromosomal crossover → Homologous recombination — Chromosomal crossover is a naturally occurring type of homologous recombination, but homologous recombination also refers to an artificial technique for introducing different DNA sequences into an organism. "Homologous recombination" has been redirecting to "Chromosomal crossover"; rather than create a different page at "Homologous recombination" (which I started to do), I think "Chromosomal crossover" should change name as it is a significant subset homologous recombination. Madeleine 01:17, 18 April 2007 (UTC)

If you really add more information, I think it will be fine to move the page. As it stands, though, the article is only about the natural version, so I can't really support the move at the moment. Dekimasuよ! 03:41, 23 April 2007 (UTC)

Well, I wasn't comfortable starting to add any information about artificial homologous recombination until this article stood as "homologous recombination", because right now that information does not belong here. But, if that's what is needed to get the move to happen, then I can go ahead and do that. -- Madeleine 04:07, 23 April 2007 (UTC)

It was requested that this article be renamed but there was no consensus for it be moved. --Stemonitis 07:09, 23 April 2007 (UTC)

I strongly feel that homologous recombination should be a separate article. Chromosomal crossover, as described in the first sentence of the current article, occurs during prophase of meiosis. However, as mentioned above, chromosomal crossover is only one type of homologous recombination. There are also other types of natural homologous recombination that would not fit into an article on "chromosomal crossover." For example, homologous recombination is necessary for certain types of DNA repair in eukaryotes and prokaryotes. Another example that could not be included in the current article is the homologous recombination that occurs following introduction of homologous DNA into a bacterium by conjugation, transduction, or natural transformation. If you look at textbooks and research articles, all of these examples are said to occur by homologous recombination, not chromosomal crossover. Therefore, a separate article entitled "homologous recombination" is necessary so that these examples can be described somewhere. At the very least, the current article should be renamed "homologous recombination" so that these other examples can be added. NighthawkJ 18:41, 23 May 2007 (UTC)

I should have mentioned other types of naturally occurring homologous recombination as well ... I've been intending to create an article for homologous recombination. I had an exchange with User:Jasu, who had created the article Gene_targeting, and he had a draft suggestion you can see if you look at the history for Homologous recombination... but then I never got around do following through. (He felt HR should be a separate article that can mention Chromosomal crossover as a main article, among others).

Your suggestion here is adding more reasons to do this. I'll try to get it done asap. Madeleine 18:57, 23 May 2007 (UTC)

? isn't this the same as synapsis? 70.246.127.92 20:23, 1 July 2007 (UTC)

I think it is best to give chromosomal crossover its own page, if not for its scientific significance then for its significance as a phenomena of the history of genetics. I do not have citable or certain examples of this, but I suggest that this be looked into. In Mendelian genetics, an allele (consisting of a "homologous pair of chromosomes" per modern genetic theory) was an unchanging factor in the phenotypes of the following generations. However, there is a phenomena, the observation and/or observer of which I do not know, that disproves this principle: the spectrum of dominance (Biology Seventh Edition, Campbell and Reece, 250-60). I am not certain about this, but I believe that chromosomal crossover is a factor of the spectrum of dominance. The spectrum of dominance also was the basis for the earlier theories of inheritance, which held that inheritance was a process of blending. I think it is worth a mention, and it would not be practical to mention it in the page for homologous recombination. Quintus Twig (talk) 01:19, 14 December 2009 (UTC)

Frequency

The article does not mention how frequently crossover occurs. Not even extreme values are given. Does it happen once in a million times? All the time? Albmont 13:23, 16 November 2007 (UTC) It happens in every cell undergoing meiosis I. —Preceding unsigned comment added by 76.226.94.200 (talk) 20:50, 28 November 2007 (UTC)

When crossover occurs how many pieces from each chromosome crossover. There are illustrations for single and double crossover, are these the only possibilities, with what frequency does each occur, i.e. roughly what proportion of crossover event are single crossover compared to double crossover. Lastly (and this might be in the text but in scientific gobbledegook) does each pair of chronosomes have one crossover event only during meosis or may it experience several successive crossover events before meosis is completed? Neutrino 16:53, 9 May 2010 (UTC)

In section "Consequences of crossover", it says," Meiotic recombination allows a more independent selection between the two alleles that occupy the positions of single genes, as recombination shuffles the allele content between sister chromatids." Should it be between non-sister

chromatids ? sister chromatids have identical DNA content, so shuffling between them would produce no change ? —Preceding unsigned comment added by 63.82.71.137 (talk) 08:44, 30 November 2007 (UTC)

I agree that a discussion on the frequency of crossovers should be one of the central components of this article. Crossover frequency, and the mechanisms that govern it, are integrally connected to the term's common usage in general genetics courses and to the entire history of recombination mapping as was developed by T.H. Morgan. Also, an article (or subset of this article) is needed to address interference, which is only a portion of the discussion on recombination frequency.

There is currently a decent description of 'interference' on the disambiguation page, but it seems like it needs a more permaneant home. (I'm appending that disambiguation text below)

"Interference (genetic) is a phenomenon by which a chromosomal crossover in one interval decreases the probability that additional crossovers will occur nearby. The distribution of crossovers by interference has been postulated to ensure that every pair of homologs receives at least one. The degree of interference and the number of crossovers per meiosis varies between organisms." —Preceding unsigned comment added by 149.169.123.210 (talk) 20:23, 17 March 2009 (UTC)

Currently the article mentions frequently in the sense that crossover involves genes at the ends of the chromosome more often than those in the middle. This fact is important for evolutionary analysis. But I still see no mention, what is the average number of times that a given homologous chromosome pair will typically cross over in any single instance of meiosis? One? Many? Fractionally many, say one crossover in tens of meiosis cycles? Cesiumfrog (talk) 04:16, 31 December 2010 (UTC)

Possible inaccuracy: "Chromosomal crossover is important in DNA repair"

This article says the following at the end of its first paragraph: "Chromosomal crossovers also occur in asexual organisms and in somatic cells, since they are important in some forms of DNA repair." I think this is incorrect. The journal article being used as a reference for this statement says: "Recombination in somatic cells is rarely associated with crossovers, and crossovers have the potential to generate genomic rearrangements and large-scale loss of heterozygosity (LOH)." (See: Li X, Heyer WD (2008). "Homologous recombination in DNA repair and DNA damage tolerance". Cell Res. 18 (1): 99–113. doi:10.1038/cr.2008.1. PMID 18166982.) To my understanding, it is exclusively non-crossover (i.e. gene conversion) products of recombination that result from accurate recombinatorial DNA repair in bacteria and somatic cells in eukaryotes. I've reworked the lead to give what I think is a more accurate description of the subject; any feedback would be appreciated. Emw (talk) 15:08, 23 October 2009 (UTC)

Wouldn't it effect repair simply in the sense that the broken gene is sometimes swapped with a working equivalent, thereby allowing a mechanism for the defective gene to be selected out from the population without also affecting all the surrounding genes? (And moreover, that recombination is intimately involved with the whole concept of maintaining homologous chromosomes, which themselves are a system for surviving damage to one version of a gene?) Even in asexual reproduction, it seems like the same processes would at least have the potential to achieve the same functions. Cesiumfrog (talk) 04:07, 31 December 2010 (UTC)

It sounds like you're referring to homologous recombination that results in non-crossover products, i.e. not chromosomal crossover. Emw (talk) 14:50, 31 December 2010 (UTC)

Not ONLY "problems"!

Several of our biology articles have a somewhat confused mixture of narrowly human and more general biological view points. I think this goes for the section titled Problems in this article, which now reads:

Although crossovers typically occur between homologous regions of matching chromosomes, similarities in sequence can result in mismatched alignments. These processes are called unbalanced recombination. Unbalanced recombination is fairly rare compared to normal recombination, but severe problems can arise if a gamete containing unbalanced recombinants becomes part of a zygote. The result can be a local duplication of genes on one chromosome and a deletion of these on the other, a translocation of part of one chromosome onto a different one, or an inversion.

It is true that gene duplication, gene deletion, and gene inversion in general have negative effects for the concerned individuals, and I suppose that therefore unbalanced recombination in a human in general may be considered as a medical problem. However, in the long run, the much rarer instances when the effects are beneficial have had a rather large positive impact on the evolution of certain lines of organisms.

I think both the negative medical effects and the rare but important positive evolutionary effects should be mentioned here. I'll make a try at rewriting the section in such a manner. JoergenB (talk) 22:40, 3 December 2013 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Chromosomal crossover/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

Rated "high" as high school/SAT biology content, part of meiosis and genetic recombination. - tameeria 23:27, 18 February 2007 (UTC)

Last edited at 23:27, 18 February 2007 (UTC). Substituted at 11:43, 29 April 2016 (UTC)

Crossover and intron/exon structure

(Warning, haven't read article, this ma be a stupid question already answered) Is it known how crossover works with reference to intron/exon boundaries? Jimw338 (talk) 13:03, 26 April 2017 (UTC)

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