b) Is the notochord present in adults? If so, what structure does it form (1 poi
ID: 199523 • Letter: B
Question
b) Is the notochord present in adults? If so, what structure does it form (1 point) ncers are frequently modular. Explain (from a developmental perspective) why a single gene may be regulated by multiple primary enhancers that each drive a different expression pattern. (2 point) b) What would determine which of the gene's enhancers was active in driving transcription of a gene in a specific tissue (e.g. a limb) at a specific time in development? Assume that the DNA is accessible (open chromatin) and that the promoter is NOT methylated.(2 points)Explanation / Answer
Among vertebrates, the notochord is retained by the adults of the lower vertebrates of class Agnatha (hagfish and lampreys), in higher vertebrates (cartilaginous fish, bony fish, reptiles, amphibians, birds, mammals) it is replaced by the vertebral column. The notochord is found on the ventral surface of the neural tube.The appearance of notochords provided an advantage for chordates. Notochords were the first "backbones," serving as support structures in chordates that lacked a bony skeleton. The very first vertebrates, such as Haikouicthys, had only a notochord. Notochords were advantageous to primitive fish-ancestors because they were a rigid structure for muscle attachment, yet flexible enough to allow more movement than, for example, the exoskeleton of the dominant animals of that time. The higher chordates were built on the foundation of this model structure, allowing the eventually development of vertebrate.
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