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Author Topic: How are Dominant and Recessive Genes different ?  (Read 7020 times)

Offline medhavika

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How are Dominant and Recessive Genes different ?
« on: 11/03/2004 16:10:10 »
i want to know that what makes some genes dominant and some recessive.how do cells know which genes they have to inherit.is there any protien which suppresses the recessive gene.

i m a freshman in biology.I dont know much about these concepts . can anyone explain me this.


 

Offline cuso4

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Re: How are Dominant and Recessive Genes different ?
« Reply #1 on: 12/03/2004 12:33:17 »
The cells don't know which gene they will inherit. We cannot be certain which cell will have which gene, we only know the probability of a cell having a certain gene.

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Offline Ylide

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Re: How are Dominant and Recessive Genes different ?
« Reply #2 on: 12/03/2004 17:35:03 »
Angel, I think what the original poster is asking is how cells that make up parts of the body that express certain phenotypes know how to do so...what is it about the dominant gene that makes it express preferentially over the recessive gene.  

You must understand that your DNA does not actively participate in the day to day manufacturing that goes on in the cell...it translates RNA which is a template if the info coded on your DNA.  My understanding from this point is that the RNA interacts with your ribosomes in such a way that only the dominant alelle of a gene is able to code its protein sequence.  (or in the case of incomplete or co-dominant, both alelles are able to)  Bear in mind that many traits are affected by more than one gene.



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Offline cuso4

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Re: How are Dominant and Recessive Genes different ?
« Reply #3 on: 12/03/2004 19:32:24 »
Oh right....and thanks Jay for the explanation.

Angel
 

Offline chris

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Re: How are Dominant and Recessive Genes different ?
« Reply #4 on: 14/03/2004 03:26:01 »
This is a very confusing issue and the use of the terminology "dominant" and "recessive" is partly to blame because these terms give the impression of a 'dominant' gene being somehow stronger and shutting off, or suppressing, the action of its counterpart.

As a general rule of thumb, both pairs of alleles (the recessive and the dominant) are expressed simultaneously, but you only see the effect of the dominant gene because it masks the effect of the recessive one.

Dominant and recessive refer to the observed phenotype - not to the expressed proteins.

You can demonstrate this using eye colour as an example.

Put simply, there are 2 genes for eye colour - B BROWN and b BLUE. Each person carries 2 eye colour genes - 1 inherited from their mother and 1 from their father. The B (brown) gene makes the iris become pigmented, whilst the b (blue) gene does not.

Therefore, for someone to have blue eyes they must have 2 copies of the b (blue) gene so that their irises contain no pigment. The presence of any number of B (brown) genes would add pigment to the irises and make the eyes look brown. So a person with one blue (b) gene and one brown (B) gene will still have brown eyes - even though the blue gene is still switched on. But the blue gene is not being suppressed or switched off by the brown gene, its effect is merely being masked.

A nice definition of a recessive trait is that a recessive gene is one which is only clinically (phenotypically) manifest in the homozygous state.

An entirely different mechanism of gene regulation is the fascinating process of imprinting - where the person you inherit a gene from dictates whether or not it is switched on. See this article about genetic imprinting for more information :

http://www.thenakedscientists.com/HTML/articles/article/katarneycolumn7.htm

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Offline MayoFlyFarmer

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Re: How are Dominant and Recessive Genes different ?
« Reply #5 on: 19/03/2004 03:38:40 »
Just remember that while they teach you "dominant vs. rcessive" in early biol classes, very few genes (especially in upper order organisms such as humans) are rarely that simple.  There are LOTS of ways that genes combine to give a phenotype.  The simplified model is very good a demonstrationg the basics of how genetics work though.

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Offline MayoFlyFarmer

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Re: How are Dominant and Recessive Genes different ?
« Reply #6 on: 19/03/2004 03:54:16 »
Also, I'm not quite sure if this is what you meant in your question about how do cells know which genes they have to inherit? but if you don't its good for someonen of your inquizitive type to hear about anyway.  If you were asking how an eye cell knows to become an eye cell, while a butt fat cell knows to become a butt fat cell, its pretty straight foreward, they become whatever the cell they divided from.  The complicated part comes during early developmental stages.  As you know all organisms start as one cell, so if you end up eventually having more than one type of cells how do they ever know what to become?  Its a very complicated process, and the very early stages of it are still some of the main tings researched by developmental biologists today, but the quick story is that that one cel divides several times into a clump of reasonable identical cells. (You've probably heard of "stem cells" but might not have know what they are Then just randomly depending on where  a cell is located in the clump it starts to become a certain type of specialized cell.  This is where some of the things that are still fuzy to me (and even the experst) happen.  But once you have even a few specialized cells they start to secrete chemicals to their neighbors that tell them "I've already decided to become a fat cell, you should become a liver cell too or else you're going to look pretty damn rediculus next to me" .  and you end up with groups of similar cells that eventually form organs.
You might ask why these cells are different from one another since they all have the same DNA.  (I posted on this earlier in a thread in the cell bio forum, but I'll give another quick explanation).  While every cell in your body has the instructions to make any protienb that you have, they have things called transcription factors that tell the cell which of those protiens to make and which not to make.  Otherwise if every cell made every protien it was capable of making, every cell would be identical.  The exciting thing about this is that as we learn more about how these work we will soon be able (and can to some degree now) to tell cells to make protiens that their TF's tell them not to (or turn off protiens that their TF's tell them to make).  For example (my fav example)  Someday (soon in my estimation) if you want a blue butt you can have one.  Why?  Because the protien that makes your eyes blue is also encoded in your butt its just turned off (repressed).  You doctor will be able to go in and simply turn that gene on, telling your butt fat cells to make blue pigment.  God I lovce this stuff!!  Good luck with your studies

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Re: How are Dominant and Recessive Genes different ?
« Reply #6 on: 19/03/2004 03:54:16 »

 

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