Question

1. In humans and in zebrafish, Hox genes will influence the eventual fate of somites along the anterior-posterior axis, causing them to develop into structures appropriate for their position on the body. Hox genes are arranged on chromosome(s) in the same order as the tissues which they affect (e.g., genes which if mutated will affect anterior structures are located to the “left” (5’) of genes which if mutated will affect posterior structures). (5’ to 3’ here refers to the direction of mRNA transcription of individual genes, and all Hox genes are transcribed in the same direction). Genes at the 5’, or anterior-body, end of the Hox array are activated first, followed by those more 3’ (posterior-body). Explain briefly how this is thought to happen- why this link between gene location and location in the animal?

Answer 1

Answer:                  This question i have to write pointswise,because it's easy to underdstand you....

• Hox genes encodes a family of transcriptional regulators that elicit distinct developmental programes along the head -to-tail axis of animals.
• The specificregional functions of individual Hox genes largely reflect their restricted expression patterns,the disruption of which can lead to development defects and disease.
• Here we examine the spectrum of molecular mechanisms controlling Hox gene expression in model vertebrates and invertebrates and find that a diverse range of mechanisms ,including nuclear dynamics.
• RNA processing, micro RNA nad translational regulation ,all concur to control Hox Gene outputs.Because of all reasons listed this is thought to happen -why this link between gene location and location in animal.
• .We Propose that this complex multi -tiered regulation might contribute to the robustness of hox expression during development;
• Hox genes provides a paradigm for several areas in modern biology . First ,from a developmental prospective ,they constitute a genetic sysem involoved in the allocation of segmental identity along animal body axes.
• As such they offer an opportunity to investigate how transcription factors organise network of subordinate genes to guide the behaviour of cell populations during morphogenesis.
• Second ,given their remarkable evolutionary conservation across distant animal phyla ,they represent an abstract system of cardial information able to operate within a wide spectrumof invertebrates and vertebrates
• bringing about the question of how the same set of developmental genes can be involoved in the generation of widely diverse developmental programmes
• Hox genes were discovered in Drosophilla , where they exist in two seperate gene clusters
• Early genetic experiments in adult flies demonstrated that Hox genes are involved in the allocation of distinct morphological identites to each body segment.
• mutations affecting specific Hox genes typically lead to homeotic transformations,in which the morphology of a given segment is transformed into the likeness of another.
• However ,understanding the mechanisms that link Hox genes to their developmental roles was only possible when the relevant genes were cloned
• and their expression domains in the fly embroys,as well as their regulation ,clarified . Indeed,molecular cloning of the BX-C followed by expression analysis showed that Hox genes are expressed in particular subdomains along the anteroposterior axis of the embryo .
• With the probable exception lampreys, vertebrates possess atleat four Hox clusters possibly as a result of successive duplications of an ancestralcluster
• Although the configuration of vertebrates Hox cluster has been interpreted as a paradigmatic form of Hox gene organism ,it might instead representa rather exceptional case of organisation and compaction that reflect intrinsic regulatory features of vertebrates Hox genes that are not necessarily present in other organisms .

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