GRE Subject Test: Biochemistry, Cell, and Molecular Biology › Help with Developmental Genes
Homeobox (Hox) genes are essential regulators of development of an organism, as they define region specific development of an embryo along its anterior-posterioir axis. A mutation in the gene Antennapedia, for example, causes Drosophila melanogaster to grow legs from its head instead of antennae.
Given that hox genes regulate segmental identity of an organism, which of the following phenotypes would possibly be present in a fruit fly with a mutation in a Hox gene required for formation of very anterior structures?
Head missing or malformed
Extra wing appendages
Missing wing appendages
Genital structures missing
Extra legs extending from thorax
The only 'very anterior' structure listed among the answers is the head. If this particular hox gene is required to create the proper anterior appendage, we can predict that of the structures listed the head is most likely to be affected.
HOX genes are a group of genes that have been well characterized to control body plan development along the anterior to posterior axis in developing embryos. What do HOX genes encode?
Transcription factors
Structural proteins
Transmembrane receptors
Golgi-endoplasmic reticulum trafficking proteins
Mitochondrial proteins
The correct answer is transcription factors. HOX transcription factors turn on genes during embryonic development to determine the type of segment structure (examples are legs or antennae) at different spatial regions of the embryo. Absence or mis-expression of HOX genes in early development renders misinformed or non-viable organisms.
RNA of Gene X was injected into the posterior of a fruit fly embryo, and the resulting embryo had two heads instead of a head and a tail. What type of protein does gene X most likely code for?
Morphogen
Growth factor
Receptor
Enzyme
Lipid
Morphogens are proteins that can regulate the patterning of embryos over a multi-cell distance. Classic morphogens were discovered by injecting cytoplasm of embryos from the anteiror to the posterior, which would give rise to an animal with two heads. Injecting cytoplasm from the posterior to the anterior would give rise to animals with two posteriors. If injecting the RNA of a particular gene changes the patterning of the animal dramatically, it is likely a morphogen.