Class Notes (835,243)
Canada (509,044)
Brock University (12,083)
Biology (1,621)
BIOL 1F25 (223)

Simple System

5 Pages
Unlock Document

Daniel Glenday

Patterning a Simple System determined = cells cannot alter their anterior/posterior identity early in development (though they can alter proximal distal identity) HOX genes - determine mammalian anterior/posterior fate HOX located on chromosome in same order as they are expressed homeotic genes - determine Drosophila anterior/posterior fate homeotic similar to HOX genes Unfertilized Drosophila egg: MATERNAL expression bicoid - mRNA expressed at head bicoid nanos - mRNA expressed at tail nanos **both code for MORPHOGENS: substances present in a gradient morphogen specify different cell fates at different concentrations** **both are TF's** Early Drosophila embryo is a SYNCITIUM syncitium before cellularization (when cells reform), gradients form bicoid expression leads to HUNCHBACK protein txn/expression Hb a threshold of bicoid is needed to activate Hb txn nanos codes for a transcriptional REPRESSOR no nanos --> Hb is expressed throughout ENTIRE embryo **bicoid and nanos create a gradient of Hb (which is itself a TF)** Hunchback regulates expression of other TF's (GAP genes) gap genes: kruppel (hunchback activates) kr knirps (hunchback represses) kni giant (hunchback represses) gt high hunchback expression --> all repressed 60% of egg length --> kruppel activated, other repressed 45% --> kruppel inactive, knirps active, giant repressed 30% --> kruppel inactive, knirps REPRESSED, giant active 0% --> kruppel inactive, knirps repressed, giant REPRESSED what represses knirps and giant repression in absence of Hb?? embryonic TAILLESS tailless Patterning a Simple System Tailless is expressed in response to Torso-Like (made by maternal torso-like anterior and posterior follicle cells) Torso-like activates Torso (RTK) – both are maternal torso Even though Torso is found all over oocyte, only the anterior and posterior ends are activated due to follicle cell localization no torso like --> no head and tail in embryo once fertilized too much TL = ubiquitous torso activation --> midsection abnormalities DORSAL/VENTRAL PATTERNING due to asymmetric nuclear localization of DORSAL in blastocyst dorsal ventral: nuclear-localized activates twist and snail represses decapentaplegic, tolloid, zerknult dorsal: cytoplasmic does not act as a TF decapentaplegic, tolloid, zerknult are expressed Pre-Fertilization: Gurken causes a differentiation of follicle cells gurken Post-Fertilization: ventral follicle cells secrete Spatzle spatzle Spatzle binds Toll (on ventral si
More Less

Related notes for BIOL 1F25

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.