Question

why is the chordate brain considered to be an enlargement of the anterior end of the neural tube​

Answer 1

Answer:

In the past 40 years, comparisons of developmental gene expression and mechanisms of development (evodevo) joined comparative morphology as tools for reconstructing long-extinct ancestral forms. Unfortunately, both approaches typically give congruent answers only with closely related organisms. Chordate nervous systems are good examples. Classical studies alone left open whether the vertebrate brain was a new structure or evolved from the anterior end of an ancestral nerve cord like that of modern amphioxus. Evodevo plus electron microscopy showed that the amphioxus brain has a diencephalic forebrain, small midbrain, hindbrain and spinal cord with parts of the genetic mechanisms for the midbrain/hindbrain boundary, zona limitans intrathalamica and neural crest. Evodevo also showed how extra genes resulting from whole-genome duplications in vertebrates facilitated evolution of new structures like neural crest. Understanding how the chordate central nervous system (CNS) evolved from that of the ancestral deuterostome has been truly challenging. The majority view is that this ancestor had a CNS with a brain that gave rise to the chordate CNS and, with loss of a discrete brain, to one of the two hemichordate nerve cords. The minority view is that this ancestor had no nerve cord; those in chordates and hemichordates evolved independently. New techniques such as phylostratigraphy may help resolve this conundrum.

Explanation:

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Answer 2

the chordate brain is considered to be an enlargement of the anterior and of the neural tube because of the developmental study of the corded plane.

Explanation:

• brain is  formed from the anterior end of the neural tube.

• the anterior end of the neural tube forms extension and enlargement. This undergoes different type of division of the cells resulting in the formation of the brain. As a result of this it is seen that due to defect in the  anterior end of the neuràl tube the development of the brain has been hampered. So the consideration is made.

To know more about development of brain,

Role of breastmilk in development of brain - Brainly.in

https://brainly.in/question/1269361