Lecture 11 - Segmentation Flashcards
Which three phyla undergo segmentation? [3]
- Arthropods
- Annelids
- Vertebrates
What do most of the structures in Drosophila arise from?
Imaginal discs
How are the segments divided in Drosophila?
- Into 14 para-segments
- These form 14 true segments at adulthood
What are three types of segmentation defects in Drosophila? [3]
- General A-P problems
- Continuous segments affected (Gap genes)
- Alternate segments affected (Pair rule)
What is a Bicoid mutant?
- A mutant with two posteriors
- Caused by loss of gene that is important in making the anterior end
What is a maternal effect mutation?
The maternal genotype effects the progeny phenotype
Where is the Bicoid located in the WT Drosophila?
At the anterior end of the embryo
How does Bicoid function?
- It is a transcription factor
- It works in the nucleus to regulate gene expression
How are the segments set up by Bicoid?
The bicoid gradient information on the distance from the anterior
Activation of [A] genes makes [B] segments in the Drosophila embryo.
A - Two
B - Three
How does Bicoid regulate its target genes?
Binds to the promoters of the target genes
What are features of the Bicoid target genes that allow for the segmental activation of them?
The promoters have different affinities and different number of binding sites for Bicoid
What is a hunchback mutant?
They have head and thorax defects
What is hunchback important for?
making anterior structures
What is the role of Nanos?
Keeps Hunchback protein out of the posterior end of the embryo
What is the krupple stripe activated by?
It is generated by Hunchback acting as a morphogen
How is gap genes expression regulated?
- By maternal effect genes
- By cross-regulation among gap genes themselves
What are gap genes?
- Transcription factors
- Help with segmentation
What are the primary pair rule genes? [3]
- even skipped
- runt
- hairy
What are the secondary pair rule genes? [5]
- sushi tarazu
- odd-paired
- odd-skipped
- paried
- sloppy-paired
What is the even-skipped pair rule gene?
Expressed in odd numbered para-segments
What is the sushi tarazu pair rule segment?
Expressed in even numbered para-segments
