Module 6 : Body plans Flashcards
What is meant by the term body plan?
the basic structural arrangement of an organism
Define what a homeobox gene is
Define what a homeobox sequence is
a group of regulatory genes with a conserved DNA sequence that guides the development of body plans
a highly conserved DNA sequence found within homeobox genes that is crucial for the development of an organisms body plan
How many base pairs long is the homeobox sequence and what does it code for?
180 base pairs long and it codes for a part of a protein that is 60 amino acids long
The part of the protein coded for by the homeobox sequence is known as what?
What is the role of this part of the protein?
the homeodomain
it binds to DNA and switches other genes on or off
Make 1 point about the homeodomain
it is highly conserved in plants , animals and fungi
What are hox genes?
In animals , hox genes are found in what formation?
What are they responsible for?
one group of homeobox genes that are only present in animals
they are found in gene clusters ( mammals have 4 clusters on different chromosomes )
the correct positioning of body parts in animals
Make 4 points about the mechanism of how hox genes control development
(start with encoding of homeodomain)
1)homeobox sequence encodes the homeodomain which is the part of the protein that binds to DNA
2)the homeodomain acts as a transcription factor
3)the homeodomain binds to DNA , switching developmental genes on or off
4)this modifies the transcription of proteins necessary for development of body plans
Hox genes can control the development of what 5 things?
-number of body layers
-symmetry of the body
-the anterior-posterior axis (ensure head is at one end and any tail is at other end)
-segmentation of the body into head , thorax , abdomen etc
-position and development of limbs , eyes and other structures
Give 3 reasons why homeobox genes are so highly conserved in animals , plants and fungi
-a mutation would have large effects by altering the organisms body plan
-many other genes would be affected by a mutation in a homeobox gene
-mutations are likely to be lethal and therefore selected against
What 2 mechanisms control the development of body plans?
Describe what each is
mitosis-results in cell division and proliferation
apoptosis-programmed cell death
Make 2 points about how mitosis and apoptosis work together to control development
What regulates both mitosis and apoptosis?
-the role of mitosis is to increase the number of cells leading to growth
-the role of apoptosis is to shape body parts by removing unwanted cells and tissues
hox genes
The expression of regulatory genes can be influenced by what ?
internal or external environmental stimuli
How to regulatory genes respond to these stimuli ?
by regulating the cell cycle and apoptosis
Make 3 points about how regulatory genes respond to internal stimuli
(start with examples of some internal stimuli and what effect these have on DNA)
-they are able to respond to internal stimuli such as stress , drugs or hormones that may cause DNA damage
-when DNA is damaged , regulatory genes trigger the cell cycle to stop and initiate apoptosis
-this prevents DNA damage being replicated into new cells
