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Homeobox Genes and Evolution. Lecture 3. 3’. Gene A. Gene B. Gene C. Gene D. 5’. Hox Gene Function. 3’. Which phenotype would you predict from loss of Gene D function?. Gene A. Gene B. Gene C. Gene D. 5’. Which phenotype would you predict from loss of Gene D function?. A. B. C. - PowerPoint PPT Presentation
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Homeobox Genes and Evolution
Lecture 3
Hox Gene Function
5’
3’
Gene A
Gene B
Gene C
Gene D
Which phenotype would you predict from loss of Gene D function?
5’
3’
Gene A
Gene B
Gene C
Gene D
Which phenotype would you predict from loss of Gene D function?
A B
C D
Hox Gene Function
5’
3’
Gene A
Gene B
Gene C
Gene D
Which phenotype would you predict from loss of Gene D function?
5’
3’
Gene A
Gene B
Gene C
Gene D
Which phenotype would you predict from loss of Gene B function?
5’
3’
Gene A
Gene B
Gene C
Gene D
Which phenotype would you predict from loss of Gene B function?
A B
C D
Hox Gene Function
5’
3’
Gene A
Gene B
Gene C
Gene D
Which phenotype would you predict from loss of Gene B function?
5’
3’
Gene A
Gene B
Gene C
Gene D
What order would you expect the Hox genes to be in on the
chromosome?• 3’-A-B-C-D-E-5’• 3’-C-A-E-B-D-5’• 3’-B-D-E-A-C-5’• 3’-D-B-E-A-C-5’
Gene D
Gene AGene E
Gene B
Gene C
Mutations in Hox genes can lead to what type of phenotype?
a. The anterior portion of the embryo does not develop
b. Several adjacent segments will be missing in an otherwise intact embryo
c. The affected segment will develop like its posterior neighbour
d. Duplication of a segment
Which statements describe the phenotype of the Hox mutant?
a. Anterior segments have been transformed into posterior ones
b. Abdominal segments develop as thoracic segments
c. Posterior segments have been transformed into anterior ones
d. An example of a homeotic transformation
mutant
Which gene is predicted to control the development of the most anterior structures?
5’ 3’A DB C
The Antennapedia Mutation
Antennapedia mutationWild-type
Why do Antennapedia (Antp) mutants have legs where their antennae should
be?• Absence of Antp gene function in the head
transforms that segment’s appendage into one normally found in the thorax
• Antp is needed for normal antennae development and is missing in these mutants
• The mutants misexpress Antp in the head, transforming that segment’s appendage into one normally found in the thorax
• They have no head
How to get legless
The vertebrae of snakes show homeosis
Pythons have >300 vertebrae
Very few cervical (no ribs) vertebrae: lost to form thoracic (rib bearing) vertebrae
Whole body resembles thorax
No forelimbs
Greatly reduced hindlimbs
Evolution of modern snakes
Hox gene expression boundaries correlate with morphological
boundaries
Changes in body plan correlate with changes in Hox expression
cerv
ical
thor
acic
lumba
r
HEAD TAIL
limb limbHoxC8
HoxC6
Chicken
What do you predict the pattern of HoxC6 and HoxC8 look like in python embryo?
thor
acic
HEAD TAIL
limb
Python
What do you predict the pattern of HoxC6 and HoxC8 look like in python embryo?
a) Same as the chicken
b) HoxC6/C8 are not expressed in python
c) HoxC6/C8 expression is expanded anteriorly and posteriorly
d) HoxC6/C8 expression is expanded anteriorly
Changes in body plan correlate with changes in Hox expression
Expansion of Hox expression domains creates thoracic, rib-bearing vertebrae along almost entire body length
Also results in loss of forelimb, through expansion of expression into anterior somites
cerv
ical
thor
acic
lumba
r
HEAD TAIL
limb limb
thor
acic
HEAD TAIL
limb
HoxC8HoxC6
HoxC8HoxC6
Chicken
Python
Role of Hox genes in evolution
1. Most, if not all, bilaterally symmetric animals, possess one or more Hox clusters that are arranged co-linear with their head to tail expression domains
2. The Hox cluster functions during development to determine head to tail organisation by controlling region specific gene expression
3. Changes in Hox gene expression can be correlated with changes in head to tail organisation
4. New body designs DO NOT require new genes, rather the modification of the function of existing ones
Role of Hox genes in evolution
1. Most, if not all, bilaterally symmetric animals, possess one or more Hox clusters that are arranged co-linear with their head to tail expression domains
2. The Hox cluster functions during development to determine head to tail organisation by controlling region specific gene expression
3. Changes in Hox gene expression can be correlated with changes in head to tail organisation
4. New body designs DO NOT require new genes, rather the modification of the function of existing ones
Role of Hox genes in evolution
1. Most, if not all, bilaterally symmetric animals, possess one or more Hox clusters that are arranged co-linear with their head to tail expression domains
2. The Hox cluster functions during development to determine head to tail organisation by controlling region specific gene expression
3. Changes in Hox gene expression can be correlated with changes in head to tail organisation
4. New body designs DO NOT require new genes, rather the modification of the function of existing ones
Role of Hox genes in evolution
1. Most, if not all, bilaterally symmetric animals, possess one or more Hox clusters that are arranged co-linear with their head to tail expression domains
2. The Hox cluster functions during development to determine head to tail organisation by controlling region specific gene expression
3. Changes in Hox gene expression can be correlated with changes in head to tail organisation
4. New body designs DO NOT require new genes, rather the modification of the function of existing ones
