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Q1: What are HOX genes responsible for in development?

A: They control anterior-posterior (A-P) patterning and determine segment identity.

Q2: What happens when HOX genes mutate?

A: They cause homeotic transformations (e.g., body segments developing inappropriate structures).

Q3: Describe the gene hierarchy in Drosophila A-P patterning.

A: Maternal effect genes → Gap genes → Pair-rule genes → Segment polarity genes → homeostatic genes.

What is the role of Bicoid in Drosophila?

A: Establishes the anterior gradient and activates genes involved in head formation.

5: What factors determine cleavage patterns?

A: Amount and distribution of yolk and spindle formation mechanisms.

What cell movements are involved in internalizing mesoderm and endoderm during gastrulation? step 1

A: Invagination, Ingression, and Delamination.

Q2: What is Invagination? in

A: A sheet of cells folds inward to form a depression or pocket. Example: Sea urchin endoderm during gastrulation.

Q3: What is Ingression? interesting

A: Individual cells migrate from the surface into the embryo’s interior, often becoming mesenchymal. Example: Primary mesenchyme cells (PMCs) in sea urchins.

Q4: What is Delamination? dances

A: A sheet of cells splits into two parallel layers, forming a new epithelial layer. Example: Formation of the hypoblast in birds.

Q5: What are the main types of cell movement used to move cells inside during gastrulation? step 2

A: Epiboly, Involution, and Migration.

Q6: What is Epiboly? everyone

A: Sheets of cells spread and thin to cover a larger area, often moving as a coherent layer. Example: Ectodermal spreading in amphibians.

Q7: What is Involution? invites

A: Cells roll inward over an edge and spread internally, often forming multiple layers. Example: Amphibian mesoderm moving under the blastopore lip.

Q8: What is Migration? moving

A: Individual cells crawl or slide within the embryo, guided by signaling cues. Example: Neural crest cells migrating to form peripheral nerves.

Q9: What is the main cell movement involved in axis elongation during gastrulation?

A: Convergent Extension.

Q10: What is Convergent Extension? cells

A: Cells intercalate mediolaterally, becoming narrower and longer to extend the body axis. Example: Elongation of the notochord in amphibians.

Q11: How does convergent extension affect the embryo?

A: It helps form the anterior-posterior (A-P) axis, creating a more elongated, organized structure.

Q9: What is the Spemann-Mangold Organizer?

A: A region that induces dorsal structures and can form a secondary axis when transplanted.

Q10: What signaling molecule stabilizes β-catenin dorsally?

A: Disheveled (Dsh).

Q11: What inhibits BMP signaling to establish the dorsal side?

A: Noggin, Chordin, and Follistatin.

Q12: What role does the Nieuwkoop Center play?

A: Establishes the dorsal organizer and signals to form the Spemann Organizer.

Q13: What is the fast block to polyspermy?

A: Membrane depolarization (from negative to positive).

Q14: How does the slow block to polyspermy work?

A: Cortical granule reaction forms the fertilization envelope.

Q15: What ion triggers the slow block to polyspermy?

A: Calcium (Ca2+).

Q20: What happens if polyspermy occurs?

A: Abnormal chromosome numbers (e.g., triploidy), leading to developmental failure.

Q21: What is the key difference between the fast and slow blocks to polyspermy?

A: Fast block: Immediate membrane depolarization.
Slow block: Cortical reaction forming a protective envelope.

In Interesting Dances, Everyone Invites Moving Cells

• Invagination - Folds inward

• Ingression - Cells move individually inward

• Delamination - Splits into two layers

• Epiboly - Spreading of a sheet

• Involution - Rolls inward

• Migration - Cells move individually

• Convergent Extension - Elongation and intercalation