What causes dominance?

[lennon]

I'd like to know what are the motives for certain genes beeign dominant?

 

 

[some people seem to believe that "beacuse they get expressed

over those that are ressesive" is an answer, I don't (I understand why they are called

dominant and what's the concept behind, what I want to know

is what's the reason for this dominance). ]

 

 

 

Is the real cause known at the present time?

[Marat]

That seems to be a good question, given that dominant genes often have negative health consequences, such as the dominant gene for Huntington's Disease.

[alpha2cen]

On the gene inheritance step we transfer some genes to the descendant.

Usually one step down descendant succeeds 1/2 of the one parents gene.

When the descendant is succeeded the gene, if the gene is dominant, the character manifestation phenomena will occur.

There are some exceptions.

One of them is the mitochondria related disease.

This gene is always succeeded from mother to child.

The percentage of succession is 100%, but the character manifestation is very small difference.

So mitochondria related gene is dominant gene.

We can decide gene dominance by using these factor , i.c., inheritance property and character manifestation property.

[lennon]

Thanks for the replys guys, alpha2cen: you clearly didn't understand my question (if you read all of it you'll see), I already knew what "dominance" means (that is, that it gets expressed).

What I asked was what's the reason for this; in other words: why does one get expressed over the other. Why does this happen. What is the physical particularity of this genes over the others, and what is the evolutionary purpose.

In reality you'll see that your answer is not really an answer at all, you just gave a definition of what the word "dominance" stand for, but not its motives.

[lemur]

Didn't you learn how to do Mendel squares in school? Dominant traits are dominant because they get expressed even when hybridized with a different gene. Recessive traits are called recessive because they do not get expressed unless both parents have them. Are you asking what causes some genes to be dominant and some to be recessive? E.g. if blue eyes is recessive and brown eyes dominant, why? It is probably because brown results from the mixing of the blue with some other pigment (I'm guessing). It probably depends on the specific trait in question what causes one expression to be dominant and another to be recessive.

[CharonY]

I believe there may be some confusion in the use of the word expressed in the context of gene expression, vs phenotype. Dominance has little to do with being expressed or not (i.e. acting on the transcriptional level) per se. However, in some cases it could be.

Both alleles can, and often are, expressed similarly. Dominance is a description on the phenotype level. For instance, an organisms has to allele of a certain enyzme. One of the alleles produces an active enzyme, the other a non-functional one (at least non-functional in terms of the specific activity we are looking for). Thus, an organism possessing both allele would be positive in enzyme activity and the the functional allele would be dominant, as it will always confer the activity, regardless of the presence of the other allele.

[alpha2cen]

I only described the dominant property from DNA level to character manifast level.

It is some different from the Mendel'method which he descrived the gene expression only one character, i.e., sphere or irregular sphere, color difference...(I think these characters are combined gen expression result), he luckly this character related to one gen expression. So he could obtain sufficient macroscopic character manifast results he desired.

[lennon]

Thanks for the replies, I appreciate that you've taken the time. It's a pitty that I didn't found what I was looking for.

-Lemur: If you read the FULL question and the comment I made to alpha2cen, you will see that is extremly clear that the second thing that you answer is what I was asking. But, your answer is completly unsatisfactory since you're guessing; wich is not even close to what I'm looking for (would it be ok for you an answer like that? I don't think so, you probably want accurate cientific data). In any case, I take it as an "I don't know". Thanks anyway.

-Charon Y: "Dominance in genetics is a relationship between two variant forms (allels) of a single gene, in which one allele masks the expression of the other in influencing some trait" (wikipedia). I tottaly understand wich expression means, understand this: the phenotype only manifests if the gene is expressed first and gets transported by the messenger RNA so that the protein can get maid (I'm not some woman that wants to know if their kids could be blond if that's what you were thinking). If you check in all of my posts, the term is used perfectly.... plus, you didn't gave any answer to my question. If you can, I would be very grateful, since I really want to know.

 

 

LET'S REPHRASE THE QUESTION:

--What is the physical particularity of this genes (the dominant ones) over the others, and what is the evolutionary purpose?

Don't tell me what dominance does or is, tell me what produces the dominance not its effects.

 

If I ask you what causes rain, you should say something like "the collition of clouds", and not "the fact that water is falling from the sky".

Edited January 17, 2011 by lennon

[CharonY]

As it is implied in my post, there is not a singular property that makes an allele dominant. It all depends on how the respective allele interacts with the organism. If it confers a trait, regardless of other alleles it is dominant. It can be because of its own activity, as in my example or due to interactions with other genes that other alleles may not be able to do. Or they fulfill certain regulatory roles differently. In other words, for each group of alleles, the mechanism will be different. Or, in other words, dominance is caused by the different mode of interplay of the respective alleles within the organism. If all are similar, no dominance is observed.

 

Asking the purpose of it is akin to asking for the purpose of rain.

Edited January 17, 2011 by CharonY

[lennon]

Well, for what you tell it seems that lemur's guess was right then.

I'll keep investigating. Thanks for the replys, everyone.