evolutionary biology

1. EVOLUTIONARY
BIOLOGY
PRESENTATION ON :-
HOMEOTIC GENES

3. ■ Homeotic gene, are a group of genes that control the pattern of body formation during early embryonic
development of organisms.
■ “The genetic control of the early embryonic development”..
■ These genes are master regulatory genes :- unfolds the genetic developmental program of body plan in various
organisms particularly the body segments or structures .
■ Each HG – encoding transcription factor proteins , which inducts the signal downstream cascade gene network
involved in body patterning .
■ Each HG – is regulated from subset of genes of HOMEOBOX .
■ Homeobox is the conserved DNA sequence of homeodomain .
■ HG genes found in many animals of echinoderms , insects , mammals and plants .

4. ■ Mutation in HG – cause displaced body parts such phenomenon called as
homeosis.
■ Mutation that lead to development of ‘ structures in an abnormal place ’
called Ectopic structures of the body are usually lethal .

5. ■ Hox gene a subset of homeotic genes .
■ Embryonic expressions in Drosophila detects segment identity .
■ Also known as Selector genes as these genes ‘select’ the identity of each segment.
■ There are 8 major Hox genes in Drosophila, located in two large gene clusters:
Antennapedia Complex Bithorax
complex
4 genes: Head and the first 3 genes: Third thoracic
segment and 8
and second thoracic segments. abdominal
segments.

6. Examples of implication of Hox mutation Homeotic
genes
Antennapedia complex (group of Homeobox genes)
5 genes that affect the anterior part of the fly when mutated, legs grow in the place of antennae
Mutation in the
form of change
in location of
genes

7. 2. Ultrabithorax
Normal Ultrabithorax gene expressed strongly in the 3rd segment of
the thorax, which bears the fly's rearmost pair of legs.
• Represses formation of wings in the 3rd segment.
Mutation in form of
inactivation of gene

8. This protein acts like a
transcription factors .
HOMEODOMAIN : 60 amino acid
protein. Forms an helix-turn-
helix .
Highly conserved protein in
animals .

9. Hox genes in humans
■ The presence of similar Hox
genes in different species reflects
their common ancestry.

10. ■ All these gene clusters work together
along the head-tail axis. Just like
Drosophila these genes are collinear they
show spatial linearity and temporal order
of gene expression.
■ Mutations in HoxD13 in humans can
cause a genetic condition called
synpolydactyly, in which people are born
with extra fingers or toes that may also be
fused together.

11. REFERENCES
■ https://www.khanacademy.org/science/biology/developmental-
biology/signaling-and-transcription-factors-in-development/a/homeotic-genes
■ https://scholar.google.co.in/scholar?q=homeotic+gene+in+drosophila&hl=en&a
s_sdt=0&as_vis=1&oi=scholart
■ https://www.sciencedirect.com/topics/neuroscience/homeobox
■ https://www.frontiersin.org/articles/10.3389/fevo.2016.00036/full

12. THANK YOU !!