Drosophila Body Plan: Hox Genes

Question 1

See middle of page 84

Answer 1

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Question 2

End page 84 start page 85. Parasegments to segments. VERY CONFUSED!

Answer 2

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Question 3

What are the segments called in drosophila head?

Answer 3

. Manipulate
. Labial
. Maxillary

Question 4

What are the segments in the drosophila thorax?

Answer 4

. T1, leg 1, no wing
. T2, leg 2, wing
. T3, leg 3, haltere

Question 5

What are the segments in the drosophila abdomen?

Answer 5

. A1-A8

Question 6

Describe the imaginal disc system of Drosophila

Answer 6

. 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

Question 7

What is Antennapedia?

Answer 7

When antennae replaces by legs

Question 8

What is homeosis?

Answer 8

Transformation of one body part into another

Question 9

How do homeotic genes alter the appearance of a segment?

Answer 9

. 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)

Question 10

What is Bithorax (mutation)?

Answer 10

Anterior compartment of haltere transformed into anterior wing (so the back wing looks like half of a front wing)

Question 11

What is a Ultrabithorax (mutation)?

Answer 11

Both anterior and posterior compartments Of haltere enlarges. So has hind wings almost identical to the fore wings.

Question 12

What are Hox genes and what gave evidence for them?

Answer 12

. Clusters of related genes on a chromosome

. Homeotic mutations mapped by Ed Lewis

Question 13

How are Hox genes thought to have arisen?

Answer 13

By tandem gene duplication

Question 14

See page 87

Answer 14

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Question 15

What did sequencing of the Hox gene Antennapedia and other homeotic genes reveal?

Answer 15

Highly conserved nucleotide sequence the homeobox

Question 16

How many base pairs/ amino acid sequence are in a homeobox?

Answer 16

180 base pairs/ 60 amino acid sequence

Question 17

The 180 base pair Hoxeobox encodes what?

Answer 17

Encodes the homeodomain in the encodes protein (69 amino acid sequence including a “helix-turn-helix”

Question 18

What does the “helix-turn -helix” (twisted protein) in the homeodomain allow?

Answer 18

Allows protein to bind to DNA- a transcription factor

Question 19

In what species are the homeobox and homeodomain pretty much the same?

Answer 19

All species

Question 20

Define a homeotic gene or homeotic selector gene

Answer 20

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

Question 21

Define homeobox

Answer 21

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

Question 22

Define a Hox gene

Answer 22

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

Question 23

The Antennapedia and bithorax bee clusters are known as what? What 3 genes are in this complex?

Answer 23

HOM-C complex (homeotic complex)

Ubx, abd-a, and Abd-B in the wild-type (controls thorax)

Question 24

Hox genes are a subset of what?

Answer 24

Homeobox genes (other gene families also contain a homeobox. So not all homeobox genes are Hox genes)

Question 25

Give an example of a homeobox gene that is not a Hox gene and why it is not one

Answer 25

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

Question 26

See all of page 89 and 91

Answer 26

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