Homeobox genes? Watch

twelve
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I just really don't get it.

Have I got this right?

They are genes which control body plan. In these genes is a segment called a homeobox, which is 180 bases long and codes for a protein which is 60 amino acids long. These proteins bind to DNA and switch on or off the process of transcription, which will determine the growth and development of that cell (so either apoptosis or specialisation). All animals have similiar homeobox genes, and so do plants, which is why our body plans are similiar.

Very confused - that doesn't quite match up with my notes or the textbook, but its the only way it makes sense to me :/ Can anyone help?
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sweety0471
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I think its how genes are aligned on a strand of DNA that codes for the positioning of different parts of the body. The numbers above are about right I duno the exact values
We always get an insect (cannot remember the name) as an example. If there is a mutation in one particular homeobox gene, then they often have a leg instead of an antennae
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Ro27
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This is my understanding..........

Homeobox genes: control the development of the body plan
Consist of 180base pairs (the homeobox) which code for polypeps of 60amino acids
SOME are transcription factors, which bind to DNA upstream and initiate transcription, thus regulating expression of other genes

They're arranged in Hox clusters, the more complicated the organism, the more clusters
They're activated and expressed from anterior to posterior
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Ro27
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(Original post by sweety0471)
I think its how genes are aligned on a strand of DNA that codes for the positioning of different parts of the body. The numbers above are about right I duno the exact values
We always get an insect (cannot remember the name) as an example. If there is a mutation in one particular homeobox gene, then they often have a leg instead of an antennae
Fruit fly
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twelve
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(Original post by sweety0471)
I think its how genes are aligned on a strand of DNA that codes for the positioning of different parts of the body. The numbers above are about right I duno the exact values
We always get an insect (cannot remember the name) as an example. If there is a mutation in one particular homeobox gene, then they often have a leg instead of an antennae
Yeah I've got that picture in my textbook, and a picture of a length of DNA and one end matches the head and one is for the tail end, but I just don't see how they actually work.


(Original post by Ro27)
This is my understanding..........

Homeobox genes: control the development of the body plan
Consist of 180base pairs (the homeobox) which code for polypeps of 60amino acids
SOME are transcription factors, which bind to DNA upstream and initiate transcription, thus regulating expression of other genes

They're arranged in Hox clusters, the more complicated the organism, the more clusters
They're activated and expressed from anterior to posterior
So you've got your DNA, and there's a section of DNA called the homeobox gene - is it within the homeobox gene that you've got the 180 base long homeobox, or is the whole thing 180 bases long? Wwhats the difference between a homeobox, and a homeobox gene?

When you say some, do you mean there are lots of homeoboxes within a homeobox gene, or there are lots of homeobox genes spread out over different chromosomes? And are the Hox clusters groups of homeobox genes, next to eachother on DNA or what?


Thank you both for your help - its probably quite simple, I just can't seem to get my head round it!
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sweety0471
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thats the one sorry if I wasn't much help
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Crazydavy
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(Original post by twelve)
....
I haven't read the other answers but this is my knowledge of it:

1. Every organism contains genes which are classed as 'homeotic genes' or you might see them called 'hox genes' OR 'homeobox genes' (these last two genes (which are the same gene but are different names for it!) only control body plan development for specific organisms like the fruit fly and most animals I'm aware of so they are the most common type of homeotic gene); I will refer to them as homeotic genes. One of these genes, like any other gene, is a section of DNA and so it would coded for by a particular series of bases.

2. The homeotic genes have regions called homeobox sequences (made up of 180 nucleotides/ bases), so there is one homeobox sequence coded for by each homeotic gene.

3. This homeobox sequence codes for a 60 amino acid long protein domain known as the homeodomain. An amino acid is made up of 3 bases (or one triplet/codon for use of other words) and so you can see that this adds up to the original 180 base section of DNA that codes for the homeobox sequence which is ultimately coding for the homeodomain.

4. This homeodomain binds to different sites on the DNA (at the start of developmental genes) so this protein acts as a transcription factor - it either activates or represses transcription on certain sites of the DNA and so alters the production of proteins which are involved in the development of the body plan.


This is all about body plans so I included that last bit to try and help you understand.

I hope this helps you get your head around it - ask if you need further help no matter how trivial it seems - I'm well aware of the amount I need to ask in order to get my head around things!

I should probably mention that I got one bit wrong. Homeotic genes are the collective name for genes that determine body plans. However you get different types of genes that code for body plans in different organisms such as the homeobox genes you mention (which are a group of related genes that specify the anterior-posterior axis and segment identity of metazoan organisms (animals i think) during early embryonic development), or others like the ParaHox gene. It shouldn't make any difference to my explanation but keep it in mind.
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twelve
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(Original post by Crazydavy)
I haven't read the other answers but this is my knowledge of it:

1. Every organism contains genes which are classed as 'homeotic genes' or you might see them called 'hox genes' OR 'homeobox genes'; I will refer to them as homeotic genes. One of these genes, like any other gene, is a section of DNA and so it would coded for by a particular series of bases.

2. The homeotic genes have regions called homeobox sequences (made up of 180 nucleotides/ bases), so there is one homeobox sequence coded for by each homeotic gene.

3. This homeobox sequence codes for a 60 amino acid long protein domain known as the homeodomain. An amino acid is made up of 3 bases (or one triplet/codon for use of other words) and so you can see that this adds up to the original 180 base section of DNA that codes for the homeobox sequence which is ultimately coding for the homeodomain.

4. This homeodomain binds to different sites on the DNA (at the start of developmental genes) so this protein acts as a transcription factor - it either activates or represses transcription on certain sites of the DNA and so alters the production of proteins which are involved in the development of the body plan.


This is all about body plans so I included that last bit to try and help you understand.

I hope this helps you get your head around it - ask if you need further help no matter how trivial it seems - I'm well aware of the amount I need to ask in order to get my head around things!
Thankyou, thats been great!
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Crazydavy
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Yea I just edited it which is kind of important to see, look at the bits in bold because I read just now that homeotic genes are the collective name for genes such as the homeobox gene.
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Crazydavy
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Haha okay one last bit edited which should clear everything up in my and your mind. I'm a bit of a perfectionist so sorry for the amount of edits but I'm learning a bit too now
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hslt
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Hox genes are a highly conserved set of genes that are expressed in an anterior-posterior fashion, and responsible for much of the anterior-posterior patterning. Typically, the more posterior you go the more hox genes are expressed (this is true for segmental structures such as rhombomeres (hindbrain precursor), somites (spine precursor), and branchial arches.

Hox genes themselves are important transcriptional regulators that control vast/complex transcriptional cascades that fate restrict cells/cell lineages (with a certain amount of plasticity etc.). They do this by binding to DNA and either directly or indirectly (by recruiting other factors) affecting the speed/efficacy/efficiency of DNA transcription. They can repress OR activate to many different degrees.

They are present in clusters, first described in drosophila (fruit fly) which has a single cluster. Interestingly the clusters are expressed in an anterior-posterior pattern that is closely correlated to how they are arranged along the DNA. Mouse have 2 or 3... (can't remember sorry) and humans have 4 clusters - hoxa hoxb hoxc and hoxd.

They are important in all sorts of things, spinal cord patterning, dermatome, limb patterning, heart, brain, blah blah, you name it it's probably affected by hox genes!

That's a very simple overview, if you want more on anything specific feel free to ask!!!

The binding of hox transcription factors does not by any means have to be at the beginning of a gene, it can be within genes (in introns) or at the end, or even 1000s of bases away at either end. (just trying to clear up something someone else said above..)
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hslt
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(Original post by twelve)
Yeah I've got that picture in my textbook, and a picture of a length of DNA and one end matches the head and one is for the tail end, but I just don't see how they actually work.
This is probably just showing the hox genes in their hox cluster. In certain regions parts of this hox cluster will be expressed.

It just so happens that the pattern of expression of hox genes anterior to posterior (or head to tail) is co-linear (i.e the same) with their organisation on DNA before they are transcribed.

They are transcribed from this length of DNA, then translated to give a protein product. This protein is a trancription factor and affects many other genes.
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Crazydavy
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(Original post by hslt)
Hox genes are a highly conserved set of genes that are expressed in an anterior-posterior fashion, and responsible for much of the anterior-posterior patterning. Typically, the more posterior you go the more hox genes are expressed (this is true for segmental structures such as rhombomeres (hindbrain precursor), somites (spine precursor), and branchial arches.

Hox genes themselves are important transcriptional regulators that control vast/complex transcriptional cascades that fate restrict cells/cell lineages (with a certain amount of plasticity etc.). They do this by binding to DNA and either directly or indirectly (by recruiting other factors) affecting the speed/efficacy/efficiency of DNA transcription. They can repress OR activate to many different degrees.

They are present in clusters, first described in drosophila (fruit fly) which has a single cluster. Interestingly the clusters are expressed in an anterior-posterior pattern that is closely correlated to how they are arranged along the DNA. Mouse have 2 or 3... (can't remember sorry) and humans have 4 clusters - hoxa hoxb hoxc and hoxd.

They are important in all sorts of things, spinal cord patterning, dermatome, limb patterning, heart, brain, blah blah, you name it it's probably affected by hox genes!

That's a very simple overview, if you want more on anything specific feel free to ask!!!

The binding of hox transcription factors does not by any means have to be at the beginning of a gene, it can be within genes (in introns) or at the end, or even 1000s of bases away at either end. (just trying to clear up something someone else said above..)
You only need to know that they can activate or repress transcription at the start of developmental genes at A2
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Revd. Mike
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I hope you all find this educational:

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Kris S
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Drosophila (fruit fly) i think
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