1. Homeobox genes and Apoptosis

2. Apoptosis Progammed cell death
Normal cells can only divide certain number of times
Balance between cell death and mitosis controlled by cell signalling – cytokines
Cancer cells immortal- damaged DNA – cell doesn’t respond to signals

3. Apoptosis in development

4. What is a Homeobox gene? Homeo = same
A gene whose activity switches a whole set of genes on or off
Strictly speaking ‘homeobox’ refers to a DNA sequence of 180 nucleotides ( ‘Homeodomain is protein coded for by homeobox)
Controls organisms body plan
Discovered in 1983

5. All animals have homeobox genes that are similar
A mouse eye homeobox gene produces an eye in Drosophila – even in wrong part of body!

7. homeobox and evolution

8. Homeobox genes are highly conserved
Homeobox genes are so fundamental any mutation will mean that the organism will not survive.
There are homeobox genes in fungi and plants too
Plant homeobox genes are similar to those in other plants but different to those in animals
Each kingdom has its own set of homeobox genes.

9. Insect body plan 3 parts Head – 3 segments fuse Thorax – 3 segments
Abdomen – 8 segments
Pair of legs from each segment

10. Drosophila Pair of wings from T2 Halteres – for balance from T3
Homeobox gene Ubx stops wing formation in T3
If mutation in both copies of Ubx wings grow in T3 instead of halteres
Can’t fly!

11. Antp homeobox Turned on in thorax Makes leg develop Turned off in head
Mutation of Antp causes it to be switched on in the head
Legs develop instead of antennae
Mice have similar homeobox – if put in fruit fly head same effect as Antp

12. Homeotic genes control specialisation of segments of body
Homeotic genes control specialisation of segments of body. Homeotic describes process by which one body part becomes like another by assuming its identitity
Mammals have homeotic genes called ‘hox’ genes
Hox genes are special types of homeobox in which genes are additionally linked (or lined up) in a sequence which relates to the pattern the genes are expressed in.

13. How do homeobox genes work?
Homeobox genes code for proteins that are transcription factors.
These bind to region of DNA and cause it to be transcribed
Switches on whole collection of other genes
Normal Antp  genes for leg

14. Homeobox genes in humans
In Humans Hox A11,D11  limbs
Drug Thalidomide affected 1 or more homeobox genes
Vitamin A can affect homeobox genes

16. fruit fly development