Hox genes

Question 1

What is homeosis?

Answer 1

Transformation of one body part to another.

Question 2

What is a homeobox?

Answer 2

Conserved region of 180 nucleotides

Question 3

What is the function of Hox genes?

Answer 3

Provide identity to segments

Question 4

What is micro evolution?

Answer 4

Infinite number of changes of infinitely small size- constant selection of v. small changes.

Question 5

What is macro evolution?

Answer 5

Cambrian explosion- took place in a long time but can’t have been many small changes. Had to be few big changes.

Question 6

What are the two key genetic factors which determine evolution?

Answer 6

Circumventing pleiotropy and event frequency.

Question 7

What types of genetic changes can there be which lead to evolution?

Answer 7

• Gene duplication and divergence: stays the same
• Protein sequence evolution: need a change to make a difference, frequent.
• Cis-regulatory sequence evolution: single nucleotide change leads to changes, frequent.

Question 8

What is an example of cis-regulatory mechanism of a Hox gene and what is the gene?

Answer 8

Closely related flies have differences in trichomes on the T2 leg. D.virilis doesn’t have a naked valley. Ubx supresses trichome formation so causes the naked valley.

If you can find phenotypic differences in closely related organisms then you can track down the region that got changed.

Question 9

What else can Hox genes regulate and give an example of that.

Answer 9

Can also regulate colouration. Separate cis-regulatory elements control yellow expression in the developing wing and body.

Question 10

When did insects appear in the world?

Answer 10

Same time plants appeared on land. They had no wings.

Question 11

Give an example of evolution of arthropods.

Answer 11

The brine shrimp Artemia has thoracic and abdominal limbs. It evolved to the fruit fly which has only thoracic limbs.

Question 12

What gene promotes and what genes repress limbs in fly embryos?

Answer 12

Distalles promotes limbs.

Ubx and AbdA Hox proteins repress limbs.

Question 13

How is limb repression controlled between different organisms?

Answer 13

Differences in C-terminal residues between fly and crustacean Ubx control whether limbs are repressed.

Question 14

What mutations contributed to the evolution of hexapoda?

Answer 14

Serine to Alanine mutations in a regulatory domain.