Body plans (complete)

Some proteins that control organisms plan activate (start) or […] (stop) transcription of developmental genes.

Some proteins that control organisms plan activate (start) or repress (stop) transcription of developmental genes.

Other proteins cause unneeded cells to […] and die.

Other proteins cause unneeded cells to break down and die.

What is a body plan

A body plan is the general structure of an organism.

Using Drosophila fruit fly explain body plan

The Drosophila fruit fly has various body parts (head, abdomen, etc.) that are arranged in a particular way — this is its body plan.

explain How proteins link to body plan

• proteins control the development of a body plan

• they help set up the basic body plan so that everything is in the right place, e.g. legs grow where legs should grow.

What does Hox genes code in terms of body plan

Hox genes code for the proteins that regulate body plan development.

Two Hox gene clusters control the development of the Drosophila body plan — […] controls the development of the head and anterior thorax (yellow in Figure 1) and the other […] (red in Figure 1).

Two Hox gene clusters control the development of the Drosophila body plan — one controls the development of the head and anterior thorax (yellow in Figure 1) and the other controls the development of the posterior thorax and abdomen (red in Figure 1).

why are Drosophila considered ‘model organisms’

scientists use them to study how genes control development, then apply their findings to other, more complex animals (like humans).

Similar Hox genes are found in animals, plants and fungi, what does this mean for body plan development

body plan development is controlled in a similar way in flies, mice, humans, etc.

What are homeobox sequences

regions in Hox genes

homeobox sequences are considered highly conserved, why?

these sequences have changed very little during the evolution of different organisms that possess these homeobox sequences.

How do Hox genes control development?

• Homeobox sequences code for a part of the protein called the homeodomain.

• The homeodomain binds to specific sites on DNA,

• enabling the protein to work as a transcription factor.

• The proteins bind to DNA at the start of developmental genes,

• activating or repressing transcription

• and so altering the production of proteins involved in the development of the body plan (see Figure 3).

Both [...] and [...] are involved in the development of body plans.

Both mitosis and apoptosis are involved in the development of body plans.

What is apoptosis?

• Apoptosis, or programmed cell death, is a highly controlled process where certain cells die and break down as a normal part of development.

What happens when apoptosis has been triggered?

he cell is broken down in a series of steps.

Apoptosis steps

What are the combined roles of mitosis, differentiation, and apoptosis in development?

Mitosis and differentiation create the bulk of the body parts, while apoptosis refines the body plan by removing unwanted structures.

Give three examples of apoptosis acting as a refining mechanism (shape or refine) during development

• Separation of digits (fingers and toes) by removing connecting tissue.

• Removal of tail cells as tadpoles metamorphose into frogs.

• Pruning of excess, unneeded nerve cells during nervous system development.

How do genes control the formation of the correct body plan during development?

• Genes controlling mitosis and apoptosis are selectively switched on and off in specific cells to balance new cell production with programmed cell death.

Give an example of an internal stimulus that regulates the cell cycle and apoptosis, and describe its effect.

DNA damage. If detected during the cell cycle, it triggers gene expression that pauses the cycle or activates apoptosis.

Give two examples of external stimuli that regulate the cell cycle or apoptosis.

• Lack of nutrient availability (stress that prevents cells from undergoing mitosis).

• Pathogen attack (triggers gene expression leading to apoptosis).