6 - ICH - Cellular control 2 - Homeobox Genes

Question 1

What are Homeobox Genes? (3)

Answer 1

• Group of genes which all contain a homeobox
  
  • Homeobox = section of DNA 180 base pairs long coding for part of a protein 60 amino acids long
• This sequence is highly conserved (Very similar in animals, plants and fungi)
• Homeobox gene part of the protein is called homeodomain, binds to DNA and switches genes on and off

Question 2

Body plans and homeobox genes

Answer 2

Embryonic development of an organism needs to ensure the correct orientation of structures and the positions of specialised structure and organs

This is controlled by homeobox genes

Question 3

How long is a hox gene?

Answer 3

180 DNA base pairs long coding for a part of a protein 60 amino acids long

Question 4

What type of gene are hox genes?

Answer 4

Regulatory genes

Question 5

What do hox genes do?

Answer 5

Determines the positioning of the body parts

• e.g eyes developing in the correct position in the head

Question 6

What is the difference between the hox genes controlling eye development in fruit flies and mice?

Answer 6

Development of eyes in fruit flies and mice is controlled by homeobox genes that have very similar base sequences even though both organisms lare shared a common ancestor approx a billion years ago

Question 7

Why are homeobox genes highly conserved?

Answer 7

Inplies that their activity is absolutely fundamental to the successful development of these organs. A mutation in a homeobox gene must be so disastrous that the organism is not able to survive

Question 8

What can homeobox genes code for? Give an example?

Answer 8

Some homeobox genes code for transcription factors i.e. polypeptides which bind to many other genes and initiate their transcription

• E.g. Lac operon

Question 9

Give an example of how mutation of homeobox genes can be fatal

Answer 9

• The drug THALIDOMIDE was taken by some pregnant women in the 1950’s, adversely affected homeobox genes controlling limb development.
• Babies were born with very short or missing limbs

Question 10

What are the fancy names for these surfaces:

• Front & back
• Top & bottom
• To develop a head

Answer 10

Front = Ventral

Back = Dorsal

Top = Anterior

Bottom = Posterior

To development a head = Cephalisation

Question 11

4 characteristics of homeobox genes

Answer 11

• Determines the body plan of an organism
• Highly conserved
• Very similar in all animals, plants and fungi
• Some can code for transcription factors

Question 12

What are Hox genes?

Answer 12

Hox genes = One group of homeobox genes thare are present in animals, they are presponsible for the correct positioning of body parts

Question 13

Where are hox genes found? (3)

Answer 13

• Found in gene clusters
• Mammals have 4 clusters on different chromosomes
• The order in which the genes appear along the chromosome is the order in which their effects are expressed in an organism

Question 14

What are dipoblastic and triboplastic animals? + Example

Answer 14

Dipoblastic = Animals with 2 primary tissue layers e.g. Worms

Tripoblastic = Animals with 3 layers of primary tissue e.g. Humans

Question 15

Name and explain 3 types of body shape symmetry

Answer 15

Radial symmetry

• Seen in dipoblastic animals e.g. Jellyfish which have no right or left side, only top and bottom

Bilateral symmetry

• Organisms have left and right side and a head and tail e.g. Humans

Asymmetry

• Seen in sponges with no lines of symmetry

Question 16

Define Metamorphosis

Answer 16

Metamorphosis = A major change in the structure of an organism as it develops from one stage of its life cycle to the next

Question 17

Define Apoptosis

Answer 17

Apoptosis = Programmed cell death

Question 18

Give an example of metamorphosis and apoptosis

Answer 18

Tadpoles → Frogs

• Loss of tadpoles tail when the cells in it die through apoptosis and are engulfed by phagocytic cells

Question 19

How is apoptosis controlled?

Answer 19

Cell signalling.

Hox genes will control both mitosis and apoptosis.

Question 20

Factors affecting the expression of regulatory genes (4)

Answer 20

Can be by the environment, internal or external.

• Stress can be defines as when the homeostatic balance within an organism is disturbed
• This is due to changes in external factors e.g. temperature or internal factors e.g. hormones released due to psychological stress
• These factors may have a greater effect during growth and developemnt of an organism