Question

2) What is the molecular reason that loss of expression of a single Hox gene due to a mutation typically transforms the segment (or group of segments) into an anterior segmental fate? 3) Discuss the concept of a "molecular address" in the Drosophila cellular blastoderm stage embryo. Be sure to discuss both which genes are involved in setting up the address and which are involved in interpreting the address. 4) Explain the reason (at the level of molecules and regulatory regions) that the pair rule gene even-skipped forms 7 bands of expression in the blastoderm embryo.

Answer 1

2.Hox gene are the homeotic gene that regulates the segments and structural developmental pattern of the body.hence these are the fate regulator gene.

Hox gene have a unique feature that they are present on the same chromosome in the same repeats in all the animals that contain this gene.Hox gene is present on chromosome 3.

Homeotic gene encodes transcription factor protein that carries a homeodomain region and are called Hox gene.Hence this is the gene that is responsible for the body structural program pattern.

If there is any mutation happened in this gene then transcription gets hampered,hence the wrong protein formation will lead to the unwanted segmental pattern.

Suppose there is a homeotic gene called Antennapedia which forms the fruit flies second pair of leg in the thorax region.But the mutation if happened to this Antennapedia gene ,then the second pair of leg extends in the fly's head like a Antenna.Thus the mutation changes segment to the anteriar fate structure.

2.In Drosophila ,the concept of molecular address comes into play wherein the protein gradient extabilish and the segmentation of the body happens due to the interaction of the genes and their transcription factors.This happens once the cellular blastoderm stage has reached during the process of embryogenesis.

Herein there are the cascade of gene activation happens. Maternal gradient gene which include bicoid and nanos,start forming the morphogen gradient.

Maternal gradient gene encode a transcription factor that regulates the expression of gap gene.These gap genes divides the embryo along the anterior/posterior axis.

Also the gap gene transcription factor regulate the expression of Pair-rule gene.This pair rule gene divides the embryo into pairs of segments.Also set the polarity of the segments by regulating the expression of segment polarity gene.

Thus the programming at the molecular level at cellular blastoderm stage address the segmentation pattern in Drosophila.

3.Pair -rule gene is the one which is responsible for the development of the embryo with its segmentation pattern.Pair-rule gene encodes the transcription factor that regulate the gap gene protein,thus regulating the pair-rule gene expression.

The mutation if happened ,then the pair rule gene causes even skipped,wherein the denticle bands of alternate segment goes missing.Thus embryo with the half number of denticles appear.