Control of developmental genes and bio questions help

PAT30DAT30 said:

i do not know why, topics regarding the control of developmental gene is just something that does not stick in my head, no matter how many time i read the information over and over again.

so can some help me and give me a easy and short explanation for the DAT.
I'm guessing that by developmental genes you're referring to the HOX genes. These are genes that control the development of specific body segments. For example, if you watch a time lap movie of Drosophila development, you'll realize that early on during development the embryo starts getting segmented. This segmentation is the result of expression of different Hox genes at different regions of the body. This expression determines what each segment of the body should become. Furthermore, after this general plan is laid out, other Hox genes within each segment are expressed, allowing the details of that segment to get developed. For example, if Hox gene#1 (Hypothetical gene) get's expressed in specific region of the body, it causes that region to develop into the head of the animal. Next, Hox gene#1 promotes the expression of Hox gene#2 in the head region. This 2nd gene allows the development of the antenas in the head region. Notice that if gene#1 doesn't get expressed, then gene#2 won't be expressed either, since Hox genes control each other's expression. The reason why we're confident that Hox genes control body segmentation and specialization is that if you expressed gene#2 in the abdomenal region of the body, then antenas start developing in that region, indicating that gene#2 is indeed in control of antena development. Interestingly, Hox genes' loci are arranged in the same order that they are expressed, on the DNA.
also i do not understand the following, so please help me with those if you could.

BIG THANKS.

pecking order>>refers to the social hierarchy within various groups of organisms. For example, you have the dominant alpha male at the top of the pecking order and more submissive males that fall underneath the alpha male.
DNA vectors (bacterial vs viral)>>DNA vectors are plasmids that are used to transfect a particular cell. Plasmids are essentially circular DNAs. Using restriction enzymes one can insert a particular gene into these plasmids. Once this is done, the plasmid can be forced into bacterial cells (via electrical shock and/or heat shock). Once inside, the cell's machinery will transcribe the gene located on that plasmid and produce the product. Viral vectors are essentially segments of viral DNA. Remember that viruses can have RNA as their genetic material as well (Retroviruse). Unlike plasmids that are transcribed independent of the host cells genome, viral vectros become incorporated into the host's genome. Then, they can either get transcribed along with the host's genome, or they can remain in a dormant state for long periods of time.
disruptive selection>>It's a form of selection that favores the two extreme genotypes within the population. Consider a population of rabbits. These animals can be White, Black, or anything in between. If the environment's background colors is comrprised of very bright and very dark colors, then individuals with white and black colors survive much better due to their superior camuflauge capabilities. Subsequently, the gene frequency corresponding to these two extremes rises within the population, while the frequency of the genes corresponding to the intermediate phenotypes drops significantly (rabbits with intermediate genotypes simply cannot camoflauge as well in such environment).
and impulse transmission.

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PAT30DAT30 said:

by control of development gene i mean how these are relate: operon, promoter, operator, lac operon and trp operson.

Lac Operon is an example of inducible system. By definition, inducible systems are systems that produce a particular product only when required. Lack operon is comprised of a cluster of 3 genes (Y, Z, and A) that collectively produce an enzyme that aids with lactose digestion. Now, there's no need to produce this enzyme if lactose is not present. So, in the absence of lactose, the Repressor (coded for by the regulatory gene) binds to the promoter (Sequence close to the operon, that contaisn the TATA box. The TATA box is simply a particular sequence that is recognized by RNA polymerase). When the promoter region is occupied by the repressor, RNA polymerase can't bind to the promoter. Subsequently, the operon is not transcribed and the enzyme is not produced. However, when lactose is present, we need the enzyme that facilitates its digestion. Subsequently, lactose (AKA Inducer) binds to the repressor. This causes the repressor to undergo a conformation change. This change causes the repressor to leave the promoter. At this point, the promoter becomes available for RNA polymerase to attach to and derive the expression of LacY, Z, A genes. Upon complete digestion of lactose (Inducer) the repressor can reattach to the promoter region and stop transcription (This makes sense, because since there is no lactose around, we don't need to produce the enzyme for it's digestion). As you can see this is a highly efficient system that only produces a particular compound when needed. Operator is simply the sequence upstream to the promoter that helps RNA polymerase to bind to the promoter more effectively.

Tryp Operon is an example of a repressible system. Trip operon is comprised of a cluster of genes that produce Triptophan. By default, this system is always turned on (unlike the inducible system that is turned off, unless we need it to produce a product) contineously producing triptophan [By turned on we mean that the repressor is not bound to the promoter, so RNA polymerase can attach and derive the expression of the genes that code for triptophan]. But why is this the case?
Well, the regulatory gene codes for the repressor just as it does in the above system. However, the repressor is initially inactive, so it cannot bind to the promoter and block transcription. This is why the system is turned on by default.
However, cells can acquire Triptophan from their environment too. Under such circumstances there's no need to produce triptophan (If you can use your neighbors wireless, you wouldn't go out an get a service for which you have to pay). So, when triptophan (AKA Corepressor) is abundant in the environment, it's taken up by the cell and it binds to the inactive repressor. The Repressor-Corepressor complex can now bind to the promoter and block transcription, so that the cell doesn't waste energy producing a molecule that it can acquire from it's surroundings for free.

another question about sex - link lethal gene from topscore

A woman carries a sex-linked lethal gene that causes spontaneous abortions, she has six children. how many of her children would you expect to be boys?
Look at the answer here:
http://forums.studentdoctor.net/showthread.php?t=646778
and finally something else, i read this somewhere but a while ago and i can not find it anymore and it is about
how the rate of having sick child will decrease as the parent start producing more children.
something like the if the parent carries the trait and the first child will be x% and the second child will be less x/2%. something like that. i do not remember the topic.
BIG THANKS

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PAT30DAT30 said:

COOL, last question (for now)

autosomal dominant inheritance vs recessive inheritance. example would be nice.

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