Ch9 - Realisator Genes

Question 1

Realisator genes

Answer 1

genes that are the targets of the homeotic gene proteins

Question 2

Realisator genes function to

Answer 2

form the specified tissue or organ primordia

Question 3

2nd thoracic segment expresses

Answer 3

Antennapedia
• prevent homeothorax gene expression
(homeothorax makes transcription factor for antennae)

Question 4

Ultrabithorax represses the expression of

Answer 4

wingless in cells that become halteres
• halteres in 3rd thoracic segment
• wingless in 2nd
(Ultrabithorax specifies 3rd thoracic segment by preventing expression of genes that would generate wing tissue)

Question 5

Distal-less gene

Answer 5

target of homeotic proteins
• necessary for limb development
• active only in the thorax
• repressed in the abdomen by Ubx and AbdA
• self-regulatory at cell cycle 11 - can’t be repressed by Ubx

Question 6

Ubx

Answer 6

• represses distal-less
• specifies parasegment 5 (thorax and legs) and
parasegment 6 (legless part of first abdominal segment)
*The time and placement within a parasegment matters
- in cell cycle 10, Ubx prevents anterior part of parasegments 5&6 from making structures of segment 4
- posterior part of segment 6 blocks formation of limb primordia by repressing distal-less
- distal-less self-regulatory in cell cycle 11 - can’t be repressed by Ubx