Drosophila Body Plan: Hox Genes Flashcards
See middle of page 84
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End page 84 start page 85. Parasegments to segments. VERY CONFUSED!
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What are the segments called in drosophila head?
. Manipulate
. Labial
. Maxillary
What are the segments in the drosophila thorax?
. T1, leg 1, no wing
. T2, leg 2, wing
. T3, leg 3, haltere
What are the segments in the drosophila abdomen?
. A1-A8
Describe the imaginal disc system of Drosophila
. Mature segments are established in the larva
. Adult ectodermal structures develop from imaginal discs
. Of of undifferentiated cells in the larva
. Each disc has its own fate and fate map. So we know what they are supposed to become
. Discs (are waiting for instructions, developmental programmes are only going to be active later on) can be subdivided and implanted into host embryos
. Will usually develop according to type
. Occasionally give rise to unexpected structures
. E.g. limb disc produces eye; eye disc produced antenna
. Described as transdetermination (when a disc does not form what it is supposed to)
. Indicated some master control system
What is Antennapedia?
When antennae replaces by legs
What is homeosis?
Transformation of one body part into another
How do homeotic genes alter the appearance of a segment?
. Mutant flies observed in 1890s with ‘inappropriate’ appendages in certain segments
. Named homeotic mutants (naturally accruing mutations- accrued in the lab when they were first used in labs)
What is Bithorax (mutation)?
Anterior compartment of haltere transformed into anterior wing (so the back wing looks like half of a front wing)
What is a Ultrabithorax (mutation)?
Both anterior and posterior compartments Of haltere enlarges. So has hind wings almost identical to the fore wings.
What are Hox genes and what gave evidence for them?
. Clusters of related genes on a chromosome
. Homeotic mutations mapped by Ed Lewis
How are Hox genes thought to have arisen?
By tandem gene duplication
See page 87
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What did sequencing of the Hox gene Antennapedia and other homeotic genes reveal?
Highly conserved nucleotide sequence the homeobox
How many base pairs/ amino acid sequence are in a homeobox?
180 base pairs/ 60 amino acid sequence
The 180 base pair Hoxeobox encodes what?
Encodes the homeodomain in the encodes protein (69 amino acid sequence including a “helix-turn-helix”
What does the “helix-turn -helix” (twisted protein) in the homeodomain allow?
Allows protein to bind to DNA- a transcription factor
In what species are the homeobox and homeodomain pretty much the same?
All species
Define a homeotic gene or homeotic selector gene
A gene which defines a region or position in the embryo (e.g. a segment). Mutations in homeotic genes (homeotic mutations) lead to transformations of one structure into another, e.g. bithorax and Antennapedia
Define homeobox
A region of DNA in homeotix genes that encodes a DNA-binding domain called the homeodomain and that is the bit that binds to DNA
Define a Hox gene
A family of homeobox-containing genes that are also part of a homeotic gene complex. (Need to contain the homeobox. Not all homeobox genes are Hox genes. It is only the Hox genes that are having this dramatic effect on the body plan. Engrailed is not a Hox gene because it doesn’t provide instructions of what structure to provide within a segment, it is just helping to define the front segment from the back but not giving information about what structures should develop
The Antennapedia and bithorax bee clusters are known as what? What 3 genes are in this complex?
HOM-C complex (homeotic complex)
Ubx, abd-a, and Abd-B in the wild-type (controls thorax)
Hox genes are a subset of what?
Homeobox genes (other gene families also contain a homeobox. So not all homeobox genes are Hox genes)
Give an example of a homeobox gene that is not a Hox gene and why it is not one
The engrailed gene is a segment polarity gene and acts as homeotic selector gene to define the posterior of the segment. It is a transcription factor containing a homeodomain but is not a Hox gene because it is not part of the HOM-C complex
See all of page 89 and 91
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