Talk:Homologous chromosome

Fall 2013 Project

Untitled

I am considering developing this page further as part of an educational assignment in Fall of 2013. If someone else is also working on this, please send me a message and let me know soon, so we donʼt duplicate initial efforts in page development. Josemags (talk) 23:17, 6 October 2013 (UTC) good god — Preceding unsigned comment added by 67.197.126.69 (talk) 22:15, 22 January 2014 (UTC)

Suggestions for Improvement

There seems to be a lot missing in terms of the origin of homologous chromosomes as well as their normal function. This is more like an expanded definition with out any application. I would advise to add in more sections outlining homologous chromosomes' effects during different portions of the life cycle. Such as including portions of this article http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3594255/ that describes Homologous Chromosomes movement and action during G₀ phase in human cells. Josemags (talk) 00:15, 7 October 2013 (UTC)

Summary of plan for development of page

This article will focus on defining homologous chromosomes and how they relate to a variety of biological processes. In particular, there will be sections focusing on the structure of homologous chromosomes, their chromosomal ends, centromeres, and interactive components. A following section will relate its structure to its function thereby describing uses of homologous chromosomes in a physiological setting. Topics of discussion for use are: homologous chromosome pairing, recombination, and inheritance. Our last section will cover other uses of homologous chromosomes, namely their involvement in repair of double-stranded breaks. Quigend (talk) 00:40, 23 October 2013 (UTC)

Working Bibliography

Here is a bibliography of relevant research to the topic of homologous chromosomes that will be used to help create this Wikipedia page:

Bibliography:

Alberts, Bruce, and A. Lewis. Molecular Biology of the Cell. 4th ed. New York: Garland Science, 2002. Print.

Gerton, Jennifer L., and R. S. Hawley. "Homologous Chromosome Interactions in Meiosis: Diversity amidst Conservation." Nature Reviews Genetics (2005): 477-87. Web. <http://www.nature.com/nrg/journal/v6/n6/abs/nrg1614.html>.

Gilbert, Scott F. Developmental Biology. 6th ed. Sunderland, MA: Sinauer Associates, 2000. Print.

Klug, William S. Concepts of Genetics. Boston, Mass.: Pearson, 2012. Print.

Moulton, Glen E. The Complete Idiot's Guide to Biology. Indianapolis, IN: Alpha, 2004. Print.

Sargent R. G., Brenneman M.A., Wilson J.H. (1997) Repair of site-specific double-bond breaks in a mammalian chromosome by homologous and illegitimate recombination. Mol. Cell Bio., 17(1):267.

Tissot, Robert, and Elliot Kaufman. "Chromosomal Inheritance." Human Genetics. University of Illinois at Chicago, n.d. Web. 14 Oct. 2013. <http://www.uic.edu/classes/bms/bms655/lesson9.html>.

Zickler D. and Kleckner N (1999) Meiotic Chromosomes: Integrating Structure and Function. Annual Review of Genetics, 33: 603-754.

Austin, TX: Landes Bioscience, 2000. Madame Curie Bioscience Database. Web. 8 Oct. 2013.

"Homologous Chromosomes." - Glossary Entry. U.S. National Library of Medicine, 23 Sept. 2013. Web. 14 Oct. 2013. <http://ghr.nlm.nih.gov/glossary%3Dhomologouschromosomes>.

More sources will be added as references as the article is being written. Stack0711 (talk) 23:45, 14 October 2013 (UTC)

Comment on the additions to the page

Thus far, we have added a brief history on the subject of homologous chromosomes, a brief section about the structure of homologous chromosomes, their role in meiosis and mitosis, problems that arise with incorrect segregation in meiosis, as well as a short section discussing the use of these chromosomes in double-strand break repairs. In comparison with the earliest edition of this article, the information presented now is more up-to-date and will allow users to gain deeper insight and knowledge into homologous chromosomes. Additional information can certainly be added, ideally in the history and problem subsections. Stack0711 (talk) 02:03, 16 November 2013 (UTC) Josemags (talk) 02:35, 16 November 2013 (UTC) Quigend (talk) 02:42, 17 November 2013 (UTC)

Thank you very much for these additions! They have improved the article immensely -- compare how things looked before to how they look now.

Unfortunately, there is a basic problem with the article -- it gives conflicting definitions of the subject. The lead sentence says "Homologous chromosomes are pairs of chromosomes which contain a paternal and maternal copy". However, the beginning of the section Structure says "Homologous chromosomes are chromosomes which contain the same genes in the same order on their chromosomal arms." Using the first definition, humans have 23 pairs of homologous chromosomes: this definition would consider chromosomes X and Y to be homologous because one sex chromosome is a paternal copy and one is a maternal copy. However, using the second definition, X and Y are not homologous -- so females have 23 pairs of homologous chromosomes and males have 22 homologous pairs and one non-homologous pair.

This problem is explored in more detail in the 23 pairs section above. I think it's something important to fix, since it implies two contradictory but valid answers to the question "How many pairs of homologous chromosomes to humans have?" -- a question that seems very likely in a high school or college biology assignment or exam. Can you please address that problem? Emw (talk) 15:03, 17 November 2013 (UTC)

23 pairs

I don't think its accurate, where it says "it refers to ... or alternatively it refers to ...". There are 23 pairs of homologous chromosomes in the human. I think there is a contradiction with other related pages, like chromatid, chromosome, etc... I don't think they are all being consist with one another

From "Structure", subsection "In humans": "Humans have 46 chromosomes, which make up 23 pairs of homologous chromosomes." I don't think that statement is correct. The X and Y chromosomes do not have the same genes, thus are not homologous. Women, with two X chromosomes, do indeed have 23 pairs. However men do not. (I am not sure if the two X chromosomes in women are normally considered homologous.) Axl ¤ [Talk] 12:25, 7 November 2013 (UTC)

Here are a few relevant definitions:

1. homologous chromosomes: "The two chromosomes from a particular pair, normally one inherited from the mother and one from the father, containing the same genetic loci in the same order". GeneReviews Illustrated Glossary, http://www.ncbi.nlm.nih.gov/books/NBK5191/#homologous-chromosomes. This is a peer-reviewed resource authored by subject experts for genetic counseling and testing terms.
2. homologous pair of chromosomes: "Two chromosomes that are alike in structure and size and that carry genetic information for the same set of hereditary characteristics." Genetics: A Conceptual Approach, 2nd edition; page G-9. This is an undergraduate genetics textbook.
3. homologous: "term used to refer to chromosomes in which one set comes from the male parent and one set comes from the female parent." Miller & Levine Biology, 2010 Student edition, page G-17. This is a popular US high school biology textbook.

So according to the first two definitions, about half of all humans have 23 homologous pairs of chromosomes (females, XX), while the other half has 22 homologous pairs, with the 23rd pair being non-homologous (males, XY).

Gene Reviews is unambiguous in this diagram; XX is a homologous pair, XY is not.

Genetics: A Conceptual Approach is slightly less committal because of some seeming internal inconsistency with its glossary's definition above. It says "The two chromosomes of a homologous pair are usually alike in structure and size, and each carries genetic information for the same set of hereditary characteristics. (An exception is the sex chromosomes, which will be discussed in Chapter 4.)" (page 22, emphasis mine.) This seems to suggest that a homologous pair can have members that are not alike in structure and size. Chapter 4 goes on to say: "Although the X and Y chromosomes are not generally homologous, they do pair and segregate into different cells in meiosis. They can pair because these chromosomes are homologous at small regions called the pseudoautosomal regions (see Figure 4.5), in which they carry the same genes." (page 79, emphasis mine.)

Miller & Levine Biology indicates that X and Y are homologous, since it defines homologous chromosomes as pairs where one member comes from the father and one member comes from the mother. (See also pages 323-325, where "homologous pair" is defined in terms of meiosis / ploidy.)

So it's not unequivocally clear whether the statement in question is completely correct or not, since sources differ in important ways about the definition of "homologous chromosomes". Specifically, it's unclear whether the facts that X and Y A) share a small region of homology (in their pseudoautosomal regions) and B) pair in meiosis are enough to make them "homologous chromosomes", or if their drastically different size and genetic content disqualify them from being homologous.

However, the sources at least agree that females have 23 pairs of homologous chromosomes (chr1-22, XX). The grey area is whether the preponderance of reliable soureces would classify males' XY chromosomes pair to be homologous or non-homologous. Emw (talk) 23:17, 16 November 2013 (UTC)

Article title, singular or plural

The lead sentence of the article is:

Homologous chromosomes are pairs of chromosomes which contain a paternal and maternal copy. These copies have the same genes in the same locations, or loci, as one another.

WP:SINGULAR says:

Use the singular form: Article titles are generally singular in form, e.g. Horse, not Horses. Exceptions include nouns that are always in a plural form in English (e.g. scissors or trousers) and the names of classes of objects (e.g. Arabic numerals or Bantu languages). For more guidance, see Naming conventions (plurals).

WP:PLURAL says:

In general only create page titles that are in the singular, unless that term is always in a plural form in English (such as scissors) or is among the exceptions such as those listed below.

So, the lead sentence defines this as a concept that only occurs in the plural (pairs), as in scissors. Is the term homologous chromosome ever used in the singular? If not, this article needs to be moved to the plural. SandyGeorgia (Talk) 16:56, 16 November 2013 (UTC)

Yes. "Homologous chromosomes" is used more often, but "homologous chromosome" is also sometimes used. Compare http://scholar.google.com/scholar?hl=en&q=%22homologous+chromosome%22, http://scholar.google.com/scholar?hl=en&q=%22homologous+chromosomes%22. (As a side note, the "class" exception for WP:SINGULAR seems rather imprecise. Protein and amino acid are certainly classes of things, but those articles' titles use the singular form.) Emw (talk) 20:45, 16 November 2013 (UTC)

Article Review

This is a relatively comprehensive article, especially the sections applying to meiosis. I especially found interesting the section on homologous chromosome functionality in DNA repair. There are a number of ways I think this article could be improved:

• "Intro": A clearer outline of the article's structure would be helpful to let readers know what is to come. Also, adding details regarding homologous chromosome activity throughout the cell cycle would be good. Adding some kind of interesting hook would help to compel readers to continue reading the rest of the article. In general, the intro should be fleshed out a little more.
• "Structure": If you can find one, I would suggest adding a picture depicting the centromere locations you mentioned to help clarify the different positions.
• "In humans": In order to rid the article of any kind of bias, the words "our" and "we" ought to be discarded from the last part of the section.
• "In meiosis": remove duplicate reference to Creighton and McClintock's work with corn chromosomes.
• "Prophase I": There seems to be too much information about the synaptoneural complex, which itself might be more applicable to the anaphase section of the article. Clearer sentences describing the steps of this process would help the section be more understandable to the average reader. Again, removing the unnecessary duplicate reference to Creighton and McClintock's work would improve the section.
• "Anaphase I": Remove the duplicate reference.
• "Nondisjunction": Trisomy and monosomy are not defined as the presence of either three or one chromosome(s) in the zygote, as if the zygote only has three or one chromosome(s). Instead, trisomy and monosomy refer to an additional two chromosomes or one less chromosome in the zygote compared to the normal zygote.
• "Embryonic death": Including this section in the Nondisjunction section would be appropriate given the overlap of information.
• "Other uses": I found this to be the most intriguing section of the article. The paragraph could be written more clearly though, especially regarding the steps involved in homologous chromosome repair of DNA.

In addition to these improvements, balancing the heavily meiosis-detailed information in the article with other material concerning mitosis would be good. Furthermore, if there is any current research going on involving homologous chromosomes that could illuminate possible discoveries, adding those experiments to the article would be beneficial. Slj758 (talk) 00:39, 23 November 2013 (UTC)

Peer Article Review

First of all, nice job on the article overall! I think the introduction provides a good general idea into the topic and adding a karyogram picture was a good idea. However, it will be better if a little more detail on Gregor Mendel’s law is added (even though it’s provided in structure section- so that readers don’t have to scroll all the way down). In the overview section, it would provide the readers with more clear understanding if some details on how chromosomes interact (crossing over, etc), not just a description that says it can be affected by crossing over. History section can be improved if some background info on how the studies were done is added (or perhaps some pictures showing experiment results). For structure section, it will provide the readers with better understanding if picture/description on four different centromere placement arrangements is added (metacentric, submetacentric, telocentric, or acrocentric – how their structure differs from each other). This is just a suggestion- for functions/ problems part, it may be great if some information on how genetic mutations can affect the segregation of homologous chromosomes during meiosis/mitosis and/or pairing of homologous chromosomes prior to separation. In addition, it would be better if more details on how homologous chromosomes work in mitosis- article is heavily based on meiosis. This is minor but- for other uses section, readers will get more clear understanding if a picture or more clear descriptions on how chromosome repair process works (such as what kind of proteins involved, etc). Great job guys, the article in general provides good details and information on homologous chromosomes. Kohw 12:04, 23 November 2013 (UTC) — Preceding unsigned comment added by Kohw (talk • contribs)

Peer article review

Nice job on the article! I think that the layout is logical and that there is a good flow of material. I especially liked the Functions sections, which I thought provided great detail on the role of chromosomes in Meiosis. I do have some suggestions: The article introduction seems brief. I think it would be appropriate to generalize some of the topics you cover later in the page, such as history of discovery of homologous chromosomes and problems (ie. nondisjuction.) The Overview paragraph is a little redundant and could be consolidated into the introduction. I also noticed that there are inline citations in the introductory paragraph. Now I’m not sure if this is an official Wikipedia rule or not, but in general article introductions do not have inline citations in their first paragraph. I think that the specific material that you cite in the introduction is general enough that you do not need to cite it. That might be something to ask Keilana or our professor about. I think it would also be helpful to write a little more on the distinction between sister chromatids and homologous chromosomes in the structure paragraph. Some molecular biology is relevant here as well too. It is not explicitly stated that chromosomes are condensed DNA. While some of this material may overlap with the chromosome Wikipedia page I think it is helpful in understanding the concepts in this page as well. Perhaps also talk about karyograms and being able to visualize condensed chromatin (homologous chromosomes) in cells. One last small comment, but for the in humans subsection, I don’t think you should use the personal plural subject (we/our) in this sentence: “So humans have two homologous chromosome sets in each of our cells, meaning we are diploid organisms.” I didn't see other personal pronouns in the article but I would avoid their usage. Overall I thought the page was appropriate in style and content to other Wikipedia articles, and I also appreciated the pictures that were included. NJSfour (talk) 23:41, 22 November 2013 (UTC)

First paragraph possible error

Is the reference to mitosis in the introductory paragraph correct? Should it refer to meiosis? — Preceding unsigned comment added by EBT111 (talk • contribs) 21:03, 14 February 2015 (UTC)

It is absolutely incorrect; homologous chromosomes do not pair during mitosis, only meiosis. Sister chromatids are paired in mitosis, but these are identical molecules, no homologous ones.173.228.119.154 (talk) 07:34, 5 March 2015 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Homologous chromosome/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 highschool/SAT biology content, part of meiosis and chromosome. - tameeria 04:53, 9 March 2007 (UTC)

Last edited at 04:53, 9 March 2007 (UTC). Substituted at 18:12, 29 April 2016 (UTC)