Flashcards in Hox Genes Deck (70):
what forms the axial skeleton?
what induces sclerotome to migrate around the notochord and neural tube?
SHH from the notochord
what is endochondrial ossification?
when sclerotome cells differntiate the cartilage (and subsequently bone) of the vertebrae and ribs
which vertebrae are fused?
the sacral vertebrae and the coccygeal vertebrae
the adult drosophila has how many segments in the head?
the adult drosophila has how many segments in the thorax?
the adult drosophila has how many segments in the abdomen?
what does each segment of the thorax produce?
a pair of legs ventrally
what do the second and third thoracic segments produce?
what does the second thoracic segment have a pair of?
what does the third thoracic segment have a pair of?
who came up with the term homeosis?
who first identified a mutation (bithorax) caused homeosis?
what did bithorax (bx) cause?
it transformed the rostral half of the haltere into rostral wing
what did bithoraxiod cause?
it transformed the caudal half of the haltere into caudal wing
who discovered ultrabithorax?
what did ultrabithorax cause?
it weakly transformed halteres into wings when heterozygous but killed the embryo when homozygous
what type of mutation are bithorax, bithoraxiod and ultrabithorax?
on which chromosome will you find the bithorax complex?
how many chromosomes do drosophila have?
who carried out detailed genetic studies of bithorax mutations?
what do infra-abdominal (iab) mutations do?
cause homeotic transformations in the abdomen
how did the bithorax complex evolve?
its member genes had been formed during evolution by gene duplication
what does a homozygous deletion of the bithorax complex cause?
it transforms the third thoracic segment and all abdominal segments into a second thoracic segment
how many genes are in the bithorax complex?
3 protein coding genes
what are the genes in the bithorax complex called?
Ulltrabithorax (Ubx), abdominal-A (abdA) and abdominal-B (AbdB)
what affects Ubx?
all bithorax mutations
what affects abdA and AbdB?
which regions do Ubx mutations affect?
3rd thoracic segment and 1st abdominal segment
which regions do abdA mutations affect?
the 2nd through 5th abdominal segments
which regions do AbdB mutations affect?
the 5th through 8th abdominal segments
what is colinearity?
the correlation between a genes chromosomal position and the segments it affects
What do gain-of-fuction Antennapedia mutations cause?
antennae to be transformed into legs with a bristle pattern that corresponds to that of the 2nd thoracic legs
where is Antp normally expressed?
in the thorax, but the dominant mutation causs it to be expressed in the head as well
what type of mutation is Antp?
what do loss-of-function Antennepedia mutations cause?
they disrupt second leg development
where is the Antp gene located?
on chromosome 3 in the antennapedia complex
what other genes does the antennepedia complex contain?
labial (lab), proboscipedia (pb), Deformed (Dfd) and Sex combs reduced (Scr)
which regions do lab, pb and Dfd affect?
progressively more caudal regions of the head
which regions does Scr affect?
the first thoracic segment
which region does Antp affect?
the second thoracic segment?
which genes are transcribed in the head?
lab, pb and Dfd
which genes are transcribed in the thorax?
Dfd, Scr, Antp and Ubx
which genes are transcribed in the abdomen?
Ubx, abdA and AbdB
homeotic genes combine to make what?
a hox code
how long is the homeobox?
how long is the homeodomain?
60 amino acids
what are homeotic proteins?
what do homeotic proteins bind to?
the regulatory regions of different target genes in the genome
what are selector genes?
transcription factors that make important cellfate decisions
who discovered that there were similar homeobox genes in vertebrates?
what was the first vertebrate homeobox to be discovered?
how many homeobox genes do most vertebrates have?
what are vertebrate homeobox genes called?
what do hox genes encode?
sequence-specific DNA binding proteins - transcription factors
where are the 39 vertebrate hox genes found?
in hox complexes
how many complexes do vertebrates have?
4 - all on different chromosomes
what are vertebrate hox genes called?
HOXA (human chromosome 7), HOXB (human chromosome 17), HOXC (human chromosome 12) and HOXD (human chromosome 2)
what are parologues?
genes at the same location in each complex and show the greatest degree of sequence similarity
along which axis are hox genes expressed?
what is the HOX code?
a unique combination of expressed HOX genes in each somite
hox genes specify a somites position along the rostral-caudal axis. true or false?
false - they specify the type of vetebrae the somite will differentiate
has homeosis been seen in humans?
yes - some people (1/200) have an extra rib attached to the seventh 'cervical' vertebra
what can having cervical rib cause?
a form of thoracic outlet syndrome due to compression of the lower trunk of the branchial plexus or subclavian artery
which HOX genes are found in all 3 complexes?
HOX4, HOX9 AND HOX13
which HOX genes are expressed in cervical somites?
HOX4 AND HOX5
which HOX genes are expressed in thoracic vertebrae?
where are HOX9-11 expressed?
in the lumbar region
what does a mutation in one of HOX9-11 cause?
a transformation of the first 4 lumbar vertebrae into rib bearing thoracic vertebrae