Body plan

Question 1

What is homeobox gnees?

Answer 1

A group of regulatory genes which are involved in controlling the way that embryos develop

Question 2

What is the Hox genes?

Answer 2

A specific type of homeobox gene that control body plan development.
A body plan is the general structure of an organism

Question 3

What is the body plan of an organism?

Answer 3

The basic pattern of the body, e.g.:
* The polarity of an organism ( head/ tail)
* Segmentation of organisms such as insects and mammals into distinct body parts
* The location at which body parts such as wings, limbs and internal organs develop

Question 4

At what stage is the body plan determined?

Answer 4

Embryo stage

Question 5

What is the similarities of homeobox gene in plants, animals and fungi?

Answer 5

They are highly conserved

Question 6

Why is homeobox gene highly conserved?

Answer 6

• Mutations that caused changes in homeobox sequences can lead to organisms that are unable to survive, so their mutated alleles are not passed on
• This strong negative selection pressure explains why homeobox sequences are conserved

Question 7

What is homeobox sequences?

Answer 7

sequence of DNA that is 180 base pairs long that codes for a part of a protein called the homeodomain

Question 8

What does homeodomain do?

Answer 8

• It binds to specific sites on DNA at the start of developmental genes and acts as a transcription factor
• This alters the production of proteins involved in the development of the body plan

Question 9

What are the two process that control development of body plan?

Answer 9

• Mitosis
• Apoptosis - programmed cell death
• Both regulated by Hox genes

Question 10

How does apoptosis occur?

Answer 10

• Enzymes inside the cell break down cell components, e.g. proteins, DNA
• The cell shrinks and begins to fragment
• Phagocytes engulf and digest the cell fragments

Question 11

What are some examples when apoptosis is needed?

Answer 11

• Digits on hands and feet are connected when they first develop. Only seperate when connecting tissue undergoes apoptosis
• Tail cells in tadpoles are removed by apoptosis as they develop into frogs
• An excess of nerve cells are produced during development of the nervous system - thos that aren’t needed undergo apoptosis

Question 12

How does apoptosis response to internal stimuli?

Answer 12

If DNA damage is detected during the cell cycle, this can result in the expression of genes which cause the cycle to be paused and can even trigger apoptosis

Question 13

How does apoptosis response to external stimuli?

Answer 13

• Stress caused by a lack of nutrient availability, could result in gene expression that prevents cells from undergoing mitosis.
• Gene expression which leads to apoptosis being triggered can also be caused by external stimulus such as attack by a pathogen

Question 14

What is necrosis?

Answer 14

The death of most or all of the cells in an organ or tissue due to disease, injury, or failure of the blood supply.