Answer:
a. Maintenance of axons.
Explanation:
Axons are not maintained by microtubules. Microtubules are used in axons as railways to transport different molecules to the terminal branches of the axon or to the soma of the neuron. Axons are maintained by a special type of cells called Schwann cells.
Hox genes, which are members of the homeotic transcription factor family, establish the segment identity of tissues within the embryo and are essential regulators of the body plan along the cranio-caudal axis (also known as the anterior-posterior axis). This means during embryogenesis, these genes expression follows a precise spatial and temporal colinearity pattern from the 3' to the 5' end of each cluster.
This indicates that Hox genes expressed anteriorly in the developing embryo are typically found at the 5′ end of the same genomic area, a phenomenon known as spatial colinearity. In comparison, those expressed posteriorly are typically found at the 3′ end of the Hox cluster.
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<span>The mechanism of descent with modification is known as "evolution". This idea of descendants of adult species being similar in most ways to their ancestors but slightly modified in some way is the basis of an entire belief system for some. For example it is not unreasonable to believe over time and generations, humans may develop an extra or altered digit on the hand to accommodate cell phone usage.</span>
