1. What determines patterning during early Drosophila development?
The patterning during early Drosophila development is not based on where the sperm enters,
but the location and interaction in the ovary between the egg and the follicular cell.
2. When are A-P and D-V axes specified during Drosophila development? How is this
different (or not) from C. elegans (or Sea urchin) early development?
A-P and D-V axes are specified during oogenesis (before fertilization). Sea urchins established
3. What are the differences between two different types of blastoderm formed sequentially
during early Drosophila development?
The two types of blastoderms are synctial blastoderm and cellular blastoderm.
Synctial blastoderm is when the nuclei share common (the same) cytoplasm after the 9 th
Cellular blastoderm is formed after the 13 division, when the cell membrane grows inwards of
the plasma membrane and the nuclei get separate which forms the cellular blastoderm.
4. Define germ band (in respect to germ layers and function).
The germ band elongates to posterior end of the embryo with the pole cells that come to the
dorsal side of the egg (posterior → dorsal side). The initial repeating patterning
(parasegments) appear at the extended germ band. The germ band retracts and the epidermal
grooves rearrange themselves to form perfect forms.
5. What are the types of genes involved in determination of anterior-posterior axis
(anterior-posterior pattern formation) in Drosophila?
Genes that are involved in the determination of the anterior-posterior axis are two sets of
maternal genes. (1) bicoid and hunchback regulate the anterior structure. (2) nanos and caudal
regulate the posterior structures. These genes then regulate the zygotic gap genes, where are
expressed in a overlapping layer. The gap genes then regulate the transcription of the pair-rule
gene, which further divdies the embryo.
6. The graph and picture below show the distribution of the bicoid protein during the early
Drosophila development. Is bicoid protein acting as a transcription or translation factor
at this point? Explain your reasoning. What does it control (expression of which
proteins)? The bicoid is concentrated in the nuclei. The bicoid protein concentration is the greatest at the
Anterior and trails off posteriorly. It acts as a transcription factor due to the high concentrations
of the bicoid protein because its it must activate the expression of target genes in the anterior
part of the embryo. Bicoid binds to activate hunchback gene.
7. Where are bicoid and nanos mRNAs produced during Drosophila oogenesis and where
are they localized in the early embryo?
Nurse cells secrete bicoid mRNA into ooctyes and the bicoid is localized in the anterior. Bicoid
protein gene activates the anterior gap genes, such as hunchback.
Nanos mRNa is secreted by the ovarian nurse cells localized in the posterior. Nano proteins
activate posterior gap genes, knirps and giants.
8. You isolate embryos laid by a female Drosophila that lacks both copies of the bicoid
gene (homozygous mutant). Describe (in 1-3 sentences or with a clearly labeled
diagram) what would be the spatial distribution of caudal protein that is made from the
corresponding maternal caudal mRNA in these mutant embryos at the syncytial
blastoderm stage. Explain in additional 1-3 sentences how and why this distribution is
different from that seen in normal embryos.
9. Thinking question (possible bonus): You inject synthetic bicoid mRNA into the middle
of the egg laid by female homozygous mutant for a bicoid. Describe (in 1-3 sentences or
with a clearly labeled diagram), what do you expect to be the spatial distribution of
caudal protein at the syncytial blastoderm stage that is made from the corresponding
maternal caudal mRNA in these embryos. Explain how this distribution is achieved in
additional 1-3 sentences.