Q24 - HOX Genes, Retinoic Acid, and Neural Tube Patterning

Theoretical 2 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Gene Regulation: Eukaryotic & Epigenetics

Neural tube in the vertebrate embryos, lies the anterior-posterior (AP) axis and creates a variety of structures. There is a large body of evidence showing that AP patterning of the vertebrate embryos is controlled by HOX genes. Spatial and temporal expression patterns of HOX genes are controlled by factors usually present as gradients in the AP axis of embryos. One of these gradients is generated by retinoic acid (RA), a derivative of vitamin A, with a maximum concentration in the posterior region of the embryos (Figure below).

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Overuse of vitamin A by pregnant women may cause abnormalities in the embryos.

B. In an embryo that has been affected by excessive amounts of RA in the early stages of embryogenesis, the forebrain may not form.

C. Loss of function of a HOX gene in the embryo may have the same effect as an excessive amount of RA.

D. In an embryo whose expression of RA nuclear receptors has been downregulated, the midbrain may develop similar to the forebrain.

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Question reproduced from IBO 2018, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)