Hox Genes Flashcards
What is homeosis
one body segment is changed into another
Mutation in the Drosophila was first discovered. The mutation of rostral half of haltere into rostral wing is called:
bithorax
How many pairs of somites do humans initially form?
42
endochondrial ossification is?
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.
What occurs in mutation Ultrabithorax?
weakly transforms the halteres into wings when heterozygous, but kills the embryo when homozygous (lethal)
What occurs in mutation bithoraxoid?
transforms the caudal haltere into caudal wing
The bithorax, bithoraxoid and ultrabithorax are examples of gain or loss of function?
loss of function
Contrabithorax is when the wings transform into halteres. Is this a loss of function?
no, it is a gain of function
Lewis demonstrated that the bithorax complex does not control the number of segments but their identity. State a proof of this demonstration.
The third thoracic segment and all abdominal segments transform into a second thoracic segment
What are the three segments in the thoracic segment?
prothorax, mesothorax and metathorax
What occurs in mutation Antennapedia?
a Gain of function mutation that transforms antenna to legs
Name the 8 homeotic genes in Drosophilia in order.
lab-pb-Dfd-scr-Antp-Ubx-abdA-AbdB
The 8 homeotic genes are found on which chromosome and are close together?
3
What is colinearity?
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
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?
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.
Genes overlap/combine to specify segmental identity. Which ones are overlap?
Dfd and Ubx.
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?
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.
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?
60 amino acids; homeodomain
Homeotic genes are what kind of genes that determine the segmental identity?
selector genes
Homeobox genes are found in bacteria. True of false
false
How many homeobox, or Hox genes, identified in mammals?
39, 4 groups
What are paralogues
Genes at the same location in each complex, e.g. HOXA1, HOXB1
and HOXD1, show the greatest degree of sequence similarity
snakes have few cervical vertebrae and a lot of thoracic vertebrae. How?
expansion of the expression of Hox 6 and Hox 8 both anteriorly and posteriorly
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?
loss of function
