Talk:Mendelian inheritance

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Older discussion[edit]

Could somebody with a better knowledge of genetics correct this sentence?

Mendel based theory on they could be both cross-pollinated between two plants or self-pollenated with just one.

silsor 04:49, Jan 23, 2004 (UTC)

Done, I think this what the author meant to say. --Lexor|Talk 10:30, 23 Feb 2004 (UTC)

Moved this from the article, I think most of this is already covered in the article and other didn't realize that this kind of information belongs in Talk, but I haven't checked closely. --Lexor|Talk 10:25, 23 Feb 2004 (UTC)

The parts of the previous version I didn't merge. Someone please have another look.

Mendel's First Law: Each adult pea plant has two genes - a gene pair - for each characteristic. The two members of each gene pair separate (segregate) randomly into the eggs or sperm of the plant, so that each egg or sperm contains only one member of each gene pair. The offspring therefore inherits one randomly selected gene from each parent for each characteristic.

The first law of Mendelian Genetics was easily illustrated due to the phenomenon of dominance. Certain characteristics, such as yellow seeds, were found to be "dominant" over other "recessive" characteristics, in this case over green seeds. A yellow-seeded plant crossed with a green-seeded plant produced offspring that were entirely yellow-seeded. However, when these yellow-seeded offspring were crossed with the original green-seeded parent strain (a procedure known as back-crossing), half of the plants in the second offspring generation bore yellow seeds and half bore green seeds. The following diagram illustrates these crossesdominant yellow characteristic and a lower-case y to indicate the recessive green characteristic. These two variants are called alleles of the gene.

YY X yy Parental generation (P)

| V Yy First generation of offspring (F1) All seeds are yellow (Y allele is dominant)

Yy X yy Second cross, F1 with green P | V Yy and yy Second generation of offspring (F2), with an equal proportion of Yy and yy

Mendel's Second Law: During the formation of sperm and egg, the segregation of alleles for one gene is independent of the segregation of alleles for another gene. This law was slightly more complex to demonstrate, requiring the statistical analysis of offspring of plants that differed in two separate characteristics. typing hands getting tired, put this demo in later


A simpler figure of a dihybrid cross can be found at Dihybrid_cross. neffk 16:24, 18 August 2006 (UTC)

Order of article?[edit]

When I came across this article, I found it rather counter-intuitive, in that Mendel's second law comes before the law of segregation, which I believe is his first. Is there a reason I'm missing for this order? The one I can think of is that the law of independent assortment (the second law) is linked to metaphase I, which comes before anaphase I in meiosis. But in my AP Biology textbook, Biology, the law of segregation precedes the law of independent assortment. Auricfuzz 01:19, Jan 19, 2005 (UTC)

I too was confused by that, and I support the reordering of these parts of the article so that Mendel's First Law comes before his Second Law. — Brim 02:36, Jan 19, 2005 (UTC)
Have changed it. AndyZ 16:26, 19 November 2005 (UTC)

Scrambled text[edit]

If the two alleles differ, then one, the dominant allele, is fully expressed in the organism's appearance; the other, the segregate during gamete production.

The above sentence doesn't make sense. I looked through the article's history and found this old version which shows that the sentence was created by splicing two pre-existing sentences and leaving out the bit in the middle. Sorry I can't fix it myself, but I don't understand the subject well enough (that's why I'm reading the article) and would probably make it worse. --Heron 19:24, 28 May 2005 (UTC)

I have fixed it; it might have been an accidental deletion. AndyZ 16:24, 19 November 2005 (UTC)

Symbols for Recessive and Dominant?[edit]

I was taught that the symbols for a recessive and a dominant trait are always the same letter, except one is capitol and one is lower case. I.e. a red flower would be symbolised as 'R', while the white flower it was being breeded with would be 'r'. Here, they are each being represented by thier individual letters. Is this correct? Was I taught wrong, or are both accepted? Thanks Poisonouslizzie 02:38, 18 November 2005 (UTC)

The normal convention is to use the same letter for both, with the dominant being represented by the capital, and the recessive by the lower case.Humpelfluch
I was also taught to write it that way; it is generally easier to use upper and lower case letters just because it is easier to see which is dominant and recessive. However, it can also be written w/ different letters, as in used in the image. This becomes important after dealing with traits that can have more than 2 alleles, for example see Blood type. AndyZ 01:19, 3 January 2006 (UTC)
The convention is to use a capital for dominant and the lowercase for recessive, both with the same letter. The letter, however, represents the recessive characteristic i.e. a flower that has a dominant red gene and a recessive white gene: the heterozygous genotype would be Ww not Rr. Dallas 06:56, 16 August 2006 (UTC)
The only time you are going to have two different letters will be when there is codominance and you have two traits being shown at once.


This article needs a lot of work. While all the information is there, it is repetitive and disorganized. In addition, some of what is describes is non-Mendelian. Let's see if we can get this thing worked up to a great article!

Parts to Mendelian inheritance[edit]

The first problem is the organization of the material. It seems to list Three "Laws." I quickly used "Mendel's Second Law" in a google search and came up with several different answers. Unfortunately, this means that the numbering for Mendel's Laws are quite suspect. However we want to organize it, there are five parts to Mendel's Laws, and each one was an important divergence from the common theories for inheritance at the time:

  1. Characters are unitary. That is, they are discrete (purple vs. white, tall vs. dwarf).
  2. Genetic characteristics have alternate forms, each inherited from the two parents. Today, we call these alleles.
  3. One allele is dominant over the other (Concept of Dominance). The phenotype reflects the dominant allele.
  4. Gametes are created by random segregation. Heterozygotic individuals produce gametes with an equal frequency of the two alleles.
  5. Different traits have independent assortment. In modern terms, genes are unlinked.

Now, how do we want these? I've seen them call Mendel's Laws, Mendel's Hypotheses, and Mendelian Principles. There are probably others. Some of the google results combined the first three principles into Mendel's First Law; Others combined the first four into Mendel's First Law.

I'm inclined to use Mendel's Five Principles or Mendel's Five Laws, and spell it out in gory detail.

Is there any preference? Or discussion of where we should go? Ted 03:38, 19 May 2006 (UTC) (Signing late)

After thinking about this and looking at various sources, I think the best way to proceed is to talk about Mendel's Five Principles, and correlate them with "Mendel's Laws" in all their messy glory. Are there really no comments? That's hard to believe after all the "discussion" on the various other genetics articles. Ted 07:29, 19 May 2006 (UTC)

Figure numbers[edit]

Figures start with fig. 3 and after that fig. 1

I moved the figures into a table so that they would be together and in order. They're a little too big to be put on separate lines. Regarding Figure 2, I'm not that happy with it since the 'short hair' trait seems to be represented by a variation in the color of the bunny. I made a different version of this that I uploaded (Image:Dihybrid cross.png). Unless anyone objects I'll use it to replace Fig. 2. Tocharianne 22:18, 21 December 2006 (UTC)
Well, no one protested so I went ahead and replaced it. (Manx cats rule!) Tocharianne 20:41, 27 December 2006 (UTC)

new section: Mendelian mutations[edit]

I added a new section to the article. I would appreciate it if someone else looked over it and makes sure it's okay. Tocharianne 16:55, 21 December 2006 (UTC)

Suggest merge from "Independent assortment"[edit]

Perhaps the Independent assortment page should be merged into this page. Segregation already redirects here and I think these topics are best covered together. Dr d12 17:23, 25 February 2007 (UTC)

I agree. -Madeleine 01:16, 28 March 2007 (UTC)
I'm starting to feel ambivalent about this, realizing that "independent assortment" exists in contrast to "genetic linkage". The article includes descriptions of the molecular basis of independent assortment that should not be placed within the mendelian genetics article -- since mendelian genetics was developed and used before a molecular basis was found. (Indeed, it contributed to the discovery of that molecular basis.) - Madeleine 15:34, 22 April 2007 (UTC)
I agree Tocharianne 01:24, 31 March 2007 (UTC)
I agree merge

Law of Dominance?[edit]

I've never heard of any law of dominance, and from reading it it just paraphrases part 3 of Mendel's First Law..I suggest we remove it, it's too redundant Out slide 03:40, 13 May 2007 (UTC)

This "law" is also known as "Law of Uniformity". While the "Law of Independent Assortment" refers to the independence of different genes on different loci and how those can be recombined in the offspring (especially in the grandchildren and downwards), the law of uniformity treats the inheritance of a single trait from different homozygotic individuals to their offspring. That some of the writeup is ambiguous may not be an argument for removing the entry... please check your books on elementary biology. (talk) 22:43, 19 January 2008 (UTC)
There is a law of Dominance that states that "in a heterozygous condition when the dominant and recessive alleles are present simultaneously, the phenotype of the organism is determined by the dominant allele and the recessive character is hidden." I am not aware of this being Mendel's own law, but this needs to be included. The other laws are "Law of Segregation" and "Law of Independant Assortmrent". The Law of Dominance is a very important law in genetics. Proquence (talk) 08:40, 26 November 2008 (UTC)
The Law of Dominance is indeed a very important law in genetics. As the Merriam-Webster states, it "proved subsequently to be subject to many limitations: because one of each pair of hereditary units dominates [emphasis added] the other in expression, characters are inherited alternatively on an all-or-nothing basis..." It is also sometimes called Mendel's Third Law, although that could be a subject of debate. This law, however, should not be thrown to the side, but should be at least mentioned in the main article. -Ano-User (talk) 00:41, 20 January 2010 (UTC)
Whaa... who removed the law of dominance?! It's a very important law! Just because we're Wikipedia doesn't mean we can change what is scientifically accepted! Kingsocarso (talk) 17:49, 7 February 2014 (UTC)

Initial acceptance (or not)[edit]

The article on Mendel says, "At first Mendel's work was rejected (and it was not widely accepted until after he died)". This article says, "Mendel's results were largely accepted". AFAIK this article is wrong, but I'll leave some time for comment before I change it. Rjm at sleepers 10:30, 14 July 2007 (UTC)

Yeah, that's weird. My understanding is that his original work wasn't accepted or rejected, rather it was ignored because people didn't understand the significance at the time (and because it had a lot of math which biologists weren't used to). The opening paragraph of this article says that when his work was rediscovered it was controversial, but then finally accepted. The History section is a little unclear as to whether his work was accepted or controversial--it probably needs to be clarified. Tocharianne 12:55, 14 July 2007 (UTC)
The strange wording appeared on 10th June, probably as vandalism. I've taken the text back to an earlier version. Rjm at sleepers 10:50, 17 July 2007 (UTC)

PROBLEM WITH ARTICLE: The history section alludes to many details of Mendel's theory/theories that have not been explained up to that point. Could someone please make this article accessible to the lay reader, who is, after all, the reader to whom this article is supposed to be addressed? This is a common problem in science articles. I have seen articles on craters of the moon which do not tell you where the crater is to be found through a telescope, and I have often seen articles on animals that include detailed taxonomies but neglect to mention in what parts of the earth the particular animal in question is to be taxonomized. The root problem here I fear is a certain vanity inherent in swottiness - authors are more concerned with looking clever in front of experts than offering their knowledge to the wider public. They care more about displaying their knowledge to those who already know the material than giving it to those who do not. —Preceding unsigned comment added by (talk) 22:53, 5 September 2008 (UTC)

Vandalization? and other issues.[edit]

Someone edited this and put some immature rude stuff in, which amused me because what loser could possibly have a beef with dear old Gregor Mendel? But anyways, this article has some animal-centric language (such as characterizing gametes as specifically egg and sperm, which they are not necessarily, or identifying parents as specifically male or female) which could be done away with. And in some places, this article seems to be more from simple english than regular english, and appears directed at small children. I think it would serve this article well the be completely rewritten by someone extraordinarily knowledgeable about Mendel (with some of the better parts salvaged), instead of some 14 year old kid who heard of him in his biology class. —Preceding unsigned comment added by (talk) 00:54, 1 April 2009 (UTC)

Help in Defining[edit]

We have two parent types (of a different species), and the resulting cross is an intermediate for the most part in phenotypes. In terms of Mendelian Genetics, even after many generations, are both parent types manifest in the hybrid population? In other words, will a few rare individuals that resemble each parent be evident as a "throwback", and if so, what is that phenomenon referred to as? Thanks. Ledboots (talk) 15:12, 13 October 2009 (UTC)

Your assumptions seem to be a jumble of blending theory and early twentieth century ideas on racial hierarcies that have little or nothing to do with Mendelianism, though there is a link to the concept of atavism. Paul B (talk) 19:38, 22 October 2009 (UTC)

Cleanup Required[edit]

This gem of an excerpt from the independent assortment section:

"mendel also do a experiment.he cross different flowers and as a result 3:1 ratio is Independent assortment occurs during meiosis I in eukaryotic organisms, specifically metaphase I of meiosis, to produce a gamete with a mixture of the organism's maternal and paternal chromosomes."

Haven't had time to read the rest of the article, but clearly this needs to be cleaned up. —Preceding unsigned comment added by (talk) 21:10, 19 October 2009 (UTC)

mendel's view[edit]

mendel' —Preceding unsigned comment added by (talk) 09:53, 16 November 2009 (UTC)


In the first paragraph, the line: "They were initially derived from the work of Gregor Mendel..." would it be "They" or "It" since it is referring to Mendelian Inheritance, not "Inheritances", right? Melara... (talk) —Preceding undated comment added 23:11, 2 December 2009 (UTC).

Reference #1[edit]

In the first reference it says "The Monk in the Garden : The Lostgvnfjvkbn nhjegj g vjf grn vnr g g jkbbn qle fa fealrlb ndk vj g cm kjlkcm m blmvdlc, mlmm cs...ii based myt project on his dumb ass shit... and Found Genius of Gregor Mendel, the Father of Genetics. Houghton Mifflin"

I have a feeling that is not the title of the book. (talk) 23:02, 6 December 2009 (UTC)


To many terms used in this article are merging ideas from the sinthethic theory of inheritance or cromosomical theory of inheritance. I think that Mendel never uses terms as genetics, homozigosis or F1/F2... So Mendel never ... "summarized his findings in two laws; the Law of Segregation and the Law of Independent Assortment." as it now claims the article. Maybe Tschermak, Correns or De Vries made it or maybe in english papers from Fisher, Bateson, Punnet or Morgan, later. I don't know when the become formally and textually "Laws". So, anyone have the source?--Bestiasonica (talk) 00:10, 12 December 2009 (UTC)

I'd like a verbatim quotation of Mendel's conclusions. What did he claim and in what terms? (And source, please.) Here or in the article on Mendel himself. Tsinfandel (talk) 15:21, 16 July 2011 (UTC)

Description of chromosomal inheritance ignores crossover[edit]

Some parts of the page correctly refer to the fact that during crossover the maternal and paternal chromosomes are paired up and mixed to produce new chromosomes for the offspring, but other parts of the page are written as if maternal or paternal chromosomes are passed down unmodified. Clement Cherlin (talk) 01:22, 3 January 2011 (UTC)

Law of Dominance[edit]

Just noting that Law of Dominance redirects here, but has still not been incorporated into the text. Danger High voltage! 17:38, 10 June 2013 (UTC)

Law of Segregation[edit]

The Law of Segregation states that every individual possesses a pair of alleles (assuming diploidy) for any particular trait and that each parent passes a randomly selected copy (allele) of only one of these to its offspring. I removed "of only one of these" since you cannot randomly select more or less than one from a pair of alleles. Maniacq (talk) 10:13, 12 February 2014 (UTC)

Numbering of Laws[edit]

The Law of independent assortment is generally considered the Third law (sometimes the second), but the law of dominance is considered the first, never the third.--Miguelferig (talk) 17:12, 13 April 2014 (UTC)