Lecture 32 - Developmental genetics II Flashcards Preview

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Why mRNAs don't diffuse freely like proteins, in the syncytium ?

Are bound to specific proteins that target them to a specific place


What's the point of having enhancers and silencers sequences near to each other (like in eve gene for example)

When repressor concentration is high, it will block the enhancer effect


Segment polarity genes: 2 functions

1. Encode components of two cell-cell signaling pathways (Hedgehog and Wingless)
2. Define A and P within each segment


Segment polarity genes: What kind of protein

TFs, secreted proteins, membrane receptors, kinases, ...


Segment polarity genes: What regulates their transcription

Pair-rule genes


What happens in segment polarity genes mutants

Segments have mirroring of one half of the segment


Cascade of TFs to regulate early drosophila embryogenesis. 5 types of genes and function

Egg-polarity genes (maternal-effect): A-P axis
Gap genes: Broad subdomains
Pair-rule genes: Individual segments identified
Segment polarity genes: Define polarity of individual segments
Segment identity genes (homeotic genes): Define identity of individual segments


(notes) what genes are responsible for forming 14 equivalent segments + what we mean by serially reiterated segments

Segment polarity genes. Serially reiterated = have equal capacity of becoming different parts of the body


Homeotic mutations meaning and name of gene category identified

Mutations in segment identity genes. Hox genes


What happens in homeotic mutants (name the phenomenon)

A particular structure is replaced by another one normally found somewhere else (homeotic transformation)


2 examples of homeotic mutations

Ultrabithorax (Ubx, a TF) : second thorax and set of wings replace halteres
Antennapedia (Antp): leg in place of antenna


Number of homeotic genes (hox genes) identified in drosophila + type of protein and common characteristic

8. all encode homeodomain family transcription factors


What's a homeodomain

A DNA binding domain with a helix-helix structure


Where the hox genes are found in the drosophila genome and particular characteristic

In 2 gene complexes (antennapedia complex and bithorax complex) on third chromosome. Colinearity: Aligned in chromosome in same order as body parts when their function is needed


What genes activate/repress hox (or selector) genes

Gap genes and pair-rule genes


Pattern of expression of hox genes

Each is expressed in specific segments and some overlap


How is hox genes transcription regulated once they are commited

Through epigenetic regulation (their faith is maintained during development) methylation or acetylation depending on segment


What will ultimately determine the structure that a segment develops

The specific hox genes that are expressed in this segment


Developing wing and developing haltere: where is Ubx expressed

Not expressed in wing. Expressed in haltere


What happens at the level of the Ubx gene in the ultrabithorax mutant

Ubx is mutant so halteres develop into a second pair of wings and thorax


How was the Ubx gene linked to the ultrabithorax mutant phenotype (how was its function uncovered ?)

Forced expression of Ubx in wings and it converted them to halteres


Name of portions of body structure that stick out of the body and hox gene that controls that

appendages (antennae, legs, wings, halteres). Gene distal-less (Dll)


When is dll expressed in appendages and in abdominal segments

Expressed in earliest stage in appendage development (about 20 cells)
Not expressed in abdominal segments


What repressed Dll expression in the abdomen and type of protein

Ubx and Abd-A (abdominal A) Hox genes. ARE TRANSCRIPTION FACTORS


In double mutants (Ubx - and Abd-A -) what happens to Dll expression in the abdominal segments

Dll is derepressed and expressed in abdominal segments


In Ubx mutants, what happens to Dll expression

Dll is derepressed in abdominal segment A1 and is expressed there


Regulatory sequences in the Dll gene

Has binding sites for several TFs, including 2 for Hox genes


What happens when the Dll gene's regulatory sequences that are binding sites for Hox genes are mutated

Dll is not repressed and is expressed in abdominal segments


What are the Dll gene regulatory sequences other than the binding sites for Ubx and Abd-A

Binding sites for segment polarity genes: sloppy-paired (slp) - anterior (halves of) segments. engrailed (en) posterior (halves of) segments


What is minimally required to repress dll expression in abdominal segments

-Ubx OR Abd-A
-Slp OR En