Hox Genes

Question 1

What is homeosis

Answer 1

one body segment is changed into another

Question 2

Mutation in the Drosophila was first discovered. The mutation of rostral half of haltere into rostral wing is called:

Answer 2

bithorax

Question 3

How many pairs of somites do humans initially form?

Answer 3

42

Question 4

endochondrial ossification is?

Answer 4

When SHH induces the schlerotome, it forms a mesenchyme that migrates around the neural tube and notochord. Endochondrial ossification is the process of schlerotome differentiating into cartilage of the vertebrae and ribs.

Question 5

What occurs in mutation Ultrabithorax?

Answer 5

weakly transforms the halteres into wings when heterozygous, but kills the embryo when homozygous (lethal)

Question 6

What occurs in mutation bithoraxoid?

Answer 6

transforms the caudal haltere into caudal wing

Question 7

The bithorax, bithoraxoid and ultrabithorax are examples of gain or loss of function?

Answer 7

loss of function

Question 8

Contrabithorax is when the wings transform into halteres. Is this a loss of function?

Answer 8

no, it is a gain of function

Question 9

Lewis demonstrated that the bithorax complex does not control the number of segments but their identity. State a proof of this demonstration.

Answer 9

The third thoracic segment and all abdominal segments transform into a second thoracic segment

Question 10

What are the three segments in the thoracic segment?

Answer 10

prothorax, mesothorax and metathorax

Question 11

What occurs in mutation Antennapedia?

Answer 11

a Gain of function mutation that transforms antenna to legs

Question 12

Name the 8 homeotic genes in Drosophilia in order.

Answer 12

lab-pb-Dfd-scr-Antp-Ubx-abdA-AbdB

Question 13

The 8 homeotic genes are found on which chromosome and are close together?

Answer 13

3

Question 14

What is colinearity?

Answer 14

Ubx-abdA-AbdB, is the same as the order
of the segments that they affect when mutated. Thus Ubx mutations affect the 3rd thoracic
and 1st abdominal segments, abdA mutations affect the 2nd through 5th abdominal segments
and AbdB mutations affect the 5th through 8th abdominal segments. This correlation between
a genes chromosomal position and the segments it affects is known as colinearity

Question 15

The flour beetle Tribolium has 9 homeotic genes, 3 on the thoracic segments, each with a pair of legs and 8 abdominal segments. Ubx and abd-A are both essential for normal abdominal development. What would happen if they are inactivated?

Answer 15

Ubx and abd-A both suppress development of legs in the abdominal region. If they are inactivated, legs would grow.
Abdominal segments will be transformed into thoracic segments.

Question 16

Genes overlap/combine to specify segmental identity. Which ones are overlap?

Answer 16

Dfd and Ubx.

Question 17

On the antero-posterior pattern of homeotic genes of drosophila, the Antp gene is on Thoracic 2, and Ubx is on T3-A1. If Ubx is inactivated, what would happen?

Answer 17

T3-A1 will not form but rather form T2 which becomes the Antp. This will be a loss of function as a pair of halteres transform into wings.

Question 18

Homeotic genes are actually transcription factors. They contain a 180bp DNA called homeobox, and this encodes how many amino acids? What is the amino acid sequence called?

Answer 18

60 amino acids; homeodomain

Question 19

Homeotic genes are what kind of genes that determine the segmental identity?

Answer 19

selector genes

Question 20

Homeobox genes are found in bacteria. True of false

Answer 20

false

Question 21

How many homeobox, or Hox genes, identified in mammals?

Answer 21

39, 4 groups

Question 22

What are paralogues

Answer 22

Genes at the same location in each complex, e.g. HOXA1, HOXB1
and HOXD1, show the greatest degree of sequence similarity

Question 23

snakes have few cervical vertebrae and a lot of thoracic vertebrae. How?

Answer 23

expansion of the expression of Hox 6 and Hox 8 both anteriorly and posteriorly

Question 24

Knockout of individual Hox 10 genes in vertebrates have little effect, but knockout of all three genes transforms lumbar to thoracic vertebrae. Is this gain or loss of function?

Answer 24

loss of function