Discuss the role of hox genes in animal development.

Segmentation is a key process in animal development defined as the serial repetition of tissue pattern along the axis of the body and allows differentiation of the developing organism. This differentiation in particular is mediated through Hox Genes. This essay will discuss their role and possible mechanisms for how they work.
What are the hox genes?
The hox genes are a set of genes that determine a segments identity. In the human there are 4 sets of 13 genes. These contain a homeobox domain which allows them to trigger the expression of various genes throughout the tissue. The exact nature of their expression is unknown however their role in patterning can be shown throughout various experiments.
Experiments in flies
The hox genes were originally discovered in the drosophila by Edward B lewis when he noticed that in some mutant drosphila some segments took the identity of segments above them. For example the drosophila expressed a pair of wings where it should have expressed a pair of legs.
The nature of the expression.
Draw expression with 3’ genes expressed anteriorly and 5’ and 3’ genes being expressed posteriorly. The identity of the segment appears to be determined by the most caudal segment and knock out will anteriorise it.
Furthermore inappropriate expression of the hox gene will cause a caudal phenotype.
Experiments in rats would cause the production sacral ribs etc.
Consider in somite formation. Do mechanism for molecular segmentation clock. The hox expression is what differentiates each somite. How is this determined. There is a retinoic acid gradient (opposite to the FGF gradient). The Hox genes have a retinoic acid response element and hence can be affected by them. This also means they are sensitive to this and hence retinoic acid is a teratogen for humans.
What other evidence for hox genes are there?
Hox genes seem to control the formation of limb buds. This is through the expression of hox genes causing tbx4/5 causing FGF8 which induces limb bud formation. Furthermore in limb formation the patterning of the cartilage is determined by hox genes. However in this case the activator of it is well studied. AER, ZPA, ectoderm activate the hox genes via FGF8, shh, and wnt. Differential expressions of each cause differential hox expression.


Popular posts from this blog

The inspector calls and how it relates to biblical parables.

The Parable of the Sower, The Good Samaritan, The Prodigal Son The Parable Of The Sower There was a farmer who went to sow some corn. He scattered the seeds in the field and the seeds fell in various places. Some of the seed fell on the path where it was eaten by birds and stepped on. Some of the seed fell on rocky ground, and the plants sprouted but dried up because the soil had no moisture. Some of the seed fell in a thorn bush and grew up but were choked by the thorns. Lastly some seed fell on good soil and the plants grew and produced lots of grains. Jesus then explains the parable and says: The seeds that fell on the path represent those who hear, but the devil comes and takes the message from the hearts and stops them from being saved. The seeds that fell on the rocky ground represent the people who except gods message gladly but it doesn’t sink in and when there faith is on the line they fade away The seeds that fall among thorn
Read more

How does Priestley convey his message in An Inspector Calls?

Being a co-founder of the Socialist Commonwealth Party, Priestley felt that his political views on socialism were very important and these views are displayed prominently throughout An Inspector Calls. Priestley uses characters to represent the different generations and also uses the Inspector as a mouthpiece to distribute his views; several critics describe the Inspector as Priestley’s alter ego. The Inspector conveys Priestley’s most important message, that a change in society’s attitude is required. Through Sheila’s words, “of course he knows. And I hate to think how much he knows that we don’t already know yet” we can see that the Inspector is believed to be an omniscient presence. He speaks as if he is divine by referring to the people as men and during his last speech he says, “If men will not learn that lesson, they will be taught it in fire and blood and anguish.” These words are influenced by Priestley’s own experiences fighting in the First World War. Portraying the Inspec
Read more

Tybalt is to blame for this tragedy - Romeo and Juliet Essay

“Tybalt is to blame for this tragedy” discuss with reference to Act 3 Scene 1 On one hand, Tybalt is heavily involved in the build up to the tragedy in Romeo and Juliet; Shakespeare portrays him as a villainous character who is the cause of several deaths and misfortune. Throughout the play Shakespeare exposes Tybalt’s violent nature and his anger is particularly shown, when Tybalt confronts Romeo and insults him in Act 3 Scene 1 saying, ‘thou art a villain’. This, in the Elizabethan period was very insulting and shows how quick Tybalt is to start fights, proving that he is hot-tempered. Critics argue that Tybalt caused the tragedy as he encourages a brawl by inviting Romeo to ‘turn and draw’. Had Tybalt not said this, Mercutio would probably not have been provoked to fight and consequently die. As a result of Mercutio’s death, Romeo killed Tybalt, forcing Romeo to leave. This led to a chain of disastrous events resulting in Romeo’s, Juliet’s and Paris’ deaths. It can also be argu
Read more

The Mayor of Casterbridge - Why is the ring at Casterbridge a suitable place for Henchard to meet Susan?

Why is the ring at Casterbridge a suitable place for Henchard to meet Susan? There are a number of reasons why the Ring could be considered a suitable place for Henchard to meet Susan. Firstly, Hardy makes it clear the Ring is not a place of happiness. It is described as a Roman amphitheatre in the heart of Casterbridge where no joy can be found, even for boys who tried to play cricket in it. He even accounts the story of a woman who murdered her husband being put at the stake in the Ring. This could suggest the Ring was a suitable place for the meeting as just as an evil woman was put to rest in the Ring, so will Henchard’s terrible and disgraceful mistake. As the Mayor of Casterbridge, Henchard is considered as a very respectable man and it would greatly damage his reputation if people discovered he had sold his wife and child. This is another reason the Ring was such a suitable place for the couple to meet as it is the “spot as being safest from observation which he cou
Read more

How does a river change along its course?

Image
Geography essay: how does a river change along its course? A river through the time that it exists changes its course from how it first began. The two parts of the river is the upper course and the lower course. These two parts of the river have very varied properties and do opposite things. Before finding out how a river changes on its course we must first know what a river does. Rivers do three main things: ·          Erosion (when water hits rocks and makes it wear away into silt) ·          Transportion (when the current of the water takes the silt with it) ·          Deposition (when the water leaves the silt behind) These things can be shown in a simple diagram: Erosion varies in the two courses. In the upper coarse vertical erosion takes place. In the lower coarse lateral erosion takes place. Other features of the upper and lower coarse are: ·          Small streams (upper) ·          Slow current (upper) ·          Mostly straight (upper) ·        
Read more

Why George R.R. Martin Reigns Supreme Over J.R.R. Tolkien

When it comes to the world of epic fantasy literature, two names stand out: George R.R. Martin and J.R.R. Tolkien. Both authors have captivated readers with their immersive worlds and richly crafted characters, but when it comes to comparing the two, George R.R. Martin undeniably takes the throne as the superior storyteller. One of the reasons why Martin surpasses Tolkien is his realistic and complex portrayal of human nature. Martin's characters are flawed, multi-dimensional, and morally ambiguous, making them relatable and compelling. He doesn't shy away from depicting the darker aspects of human behavior, such as political intrigue, betrayal, and the consequences of power struggles. In contrast, Tolkien's characters tend to be more archetypal, with clear-cut divisions between good and evil, and less depth in their motivations and actions. Furthermore, Martin's world-building is unparalleled in its intricacy and detail. The fictional realm of Westeros in his "A S
Read more