L20 - Hox genes Flashcards
what is hox gene
establishes orientation of body parts in embryo
what is homeotic mutation
transformation of one body part to another,
so correct tissue but in wrong place
example of homeotic mutation in fruit fly
3rd thoracic segment mutates into another 2nd thoracic segment
so another set of wings is made
typical characteristics of hox genes
evolutionary conserved
transcription factors
homeodomain: acts as a dna binding motif
found clustered in genome
by what mechanism to genes initially duplicated
tandem gene duplication
paralogous genes
duplicated genes within a single genome
orthologous genes
same gene in diff organisms
2 mechanisms subfunctionalisation can occur
change in protein sequence
cahnge in the time/place of expression
what happens if duplicated gene isnt subfunctionalised
ends up getting removed
what is segmental duplication
vry big tandem duplication
like a whole chunk of chromosome is duplicated
what are two ways whole genome duplication events can occur
allotetrapolidy
autotetraploidy
allotetraploidy
hybridisation between two seperate species that causes 4n cell
autotetraploidy
improper meiosis resulting in 2n germ cells
a 2n combines with another 2n germ cell
to give 4n
how would u distinguish between autotetraploidy and allotetraploidy
allo has more differences in the genome
naturally cuz it’s two diff species
auto has less differences
2R hypothesis
basically says that vertebrates went through 2 whole genome duplication events in their ancestry
each with some gene loss events after
eventually resulting in the gene clusters we see today
how many hox genes in human
39
same as mouse
we acc share the same orthologous genes as mice
4 clsuters on 4 diff chromosomes
why deos chick have 14 cervical vertebrate but mouse has 7
in their hox genes
C5 and C6 fall at the boundary of where cervical ends and thoracic begins
and in a chick, the boundary is at position 14
in a mouse its at position 7
hence hox genes determine positioning and boundaries of anatomical features
what body part is affected by mutations in hox genes that control proximal-distal identities
limbs
so a mutation can get rid of femurs or ur radius
these genes originally pattern body axis, but during duplication, evolved to pattern limb orientation
general rules about vertebrate hox genes:
how are hox genes generated
tandem and segmental duplication events
general rules about vertebrate hox genes:
what do the ‘spacial domains’ of hox genes indicate
anterior posterior orientation
so as you go along, the genes will pattern for more posterior body parts
general rules about vertebrate hox genes:
what does it mean when we say hox genes have spatial and temporal colinearity
their spatial collinearity is relation between ordering of Hox genes along the chromosome and their expression patterns along the head-tail axis
temporal colinearity is the relaition between the spatial ordering of the cluster and the time that they’re expressed
