genetic witches in evo devo

Genetics as it applies to evolution, molecular biology, and medical aspects.

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joneall
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genetic witches in evo devo

Post by joneall » Wed May 04, 2016 2:24 pm

I am reading Sean Carroll's "Endless forms most beautiful" and trying to understand genetic switches. I have trouble seeing the big picture -- how to put it all together.

I will explain my current perception of the process in the hope you can either correct my errors or add the pieces I am missing -- or both!

It seems to me we start with three objects.

(1) a gene in the DNA of an organism (e.g., a fly or a frog)

(2) an operator or switch (in Carroll's terminology) for the gene

Q1: Is the operator just upstream from the gene on the DNA? If not, how does the switch know which gene it is regulating?

(3) a tool kit (TK) gene, say Pax-6 (for making eyes), which exists somewhere else in the object's DNA

The process then goes like this (I think...):

(a) First, the TK gene expresses a protein domain which is a DNA-binding protein and a transcription factor for an eye.

Q2: What regulates the expression of the TK gene?

(b) Next, the t-factor binds to the switch, or operator (pick your terminology).

(c) The switch then activates (or not, depending on the example) the production of an eye. This will correspond somehow to the gene (number 1).

Q3: What indicates the type of organism (fly or frog)?

Q4: What says where to put the eye? It clearly has something to do with the 1st gene.

Hope my problem is clear. Thanks in advance for any and all assistance.

claudepa
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Re: genetic witches in evo devo

Post by claudepa » Thu May 05, 2016 6:04 pm

I have some answers not all.
I am reading Sean Carroll's "Endless forms most beautiful" and trying to understand genetic switches. I have trouble seeing the big picture -- how to put it all together.

I will explain my current perception of the process in the hope you can either correct my errors or add the pieces I am missing -- or both!

It seems to me we start with three objects.

(1) a gene in the DNA of an organism (e.g., a fly or a frog)

(2) an operator or switch (in Carroll's terminology) for the gene

Q1: Is the operator just upstream from the gene on the DNA? If not, how does the switch know which gene it is regulating?
In biology the operator is a DNA sequence, generally located before the gene itself, and called a promotor. The transcription factors bind on this promotor on specific sequences. The contact between these transcription factors and the RNA polymerase 2 complex activates the RNA polymerase 2 with then synthetizes the gene mRNA by adding complementary nucléotides to the Template strand of the gene DNA.
(3) a tool kit (TK) gene, say Pax-6 (for making eyes), which exists somewhere else in the object's DNA

The process then goes like this (I think...):

(a) First, the TK gene expresses a protein domain which is a DNA-binding protein and a transcription factor for an eye.

Q2: What regulates the expression of the TK gene?
There is a cascade(from the begining of development) of transcrition factors activating other transcription factor. The real question is how is activated the first one ?
(b) Next, the t-factor binds to the switch, or operator (pick your terminology).

(c) The switch then activates (or not, depending on the example) the production of an eye. This will correspond somehow to the gene (number 1).
All the genes coding for the eye are next to each other on DNA and can be activated like if it was only one gene. In fact our tridimensionnal body is already coded in one dimension in our DNA !!
Q3: What indicates the type of organism (fly or frog)?
The DNA of a fly and of a frog are completely different. Your DNA and my DNA are similar at 99.9 %

Q4: What says where to put the eye? It clearly has something to do with the 1st gene.
In the embryo cells which will form the different organs migrate in their future location.

Hope my problem is clear. Thanks in advance for any and all assistance.
I hope this bring some answers but I am a cell biologist and not a specialist of embryology and development.

joneall

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