Body Plans 19.3 Flashcards
Why are fruit flies investigated for genetic studies?
They are small, easy to keep and have a short life cycle. Sometimes they have legs growing on their head or extra wings
Homeobox genes
These are regulatory genes that code for transcription factors that aid development. They contain a homeobox which is a piece of DNA that codes for a protein that binds to DNA and switches genes on or off.
Why are homeobox genes similar?
They are similar because they all code for proteins that bind to similar regions of DNA.
What can happen if there’s a mutation in the homeobox genes?
The transcription factors will be mutated so won’t be able to bind to the promoters and genes won’t be switched on or off normally so this can lead to big issues.
Pax 6 gene
This is a gene present in mice, flies and humans. It causes blindness if mutated in al 3 species so it suggests that Pax 6 is involved in the development of the eyes.
Hox genes
One group of homeobox genes present in animals and are responsible for the correct positioning of body parts. In animals, hox genes are found in hox clusters.
What is a body plan?
This is represented by a cross-section of the organism and shows the arrangement of tissue layers. Diploblastic animals have 2 primary tissue layers whereas triploblastic have 3.
Why do we have hox genes in different parts of our body?
We are segmented which means we have different segments and we need hox clusters to regulate these. We have hox genes in our head to control mouthparts, and in the thorax to control limbs etc… In an embryo these segments are called somites and the somites are directed by the hox genes to develop in a particular way.
Radial Symmetry
This is seen in diploblastic animals as they only have symmetry on the top and bottom
Bilateral Symmetry
This is seen in most animals where they have left and right sides and a head and tail.
What processes are used to shape organisms?
Mitosis - cell division
Apoptosis - programmed cell death
How does the shaping of an organism take place?
Mitosis is in charge of increasing the number of cells so the tissue grows and apoptosis is in charge of removing tissue in order to give a shape to the organism like a sculptor with clay. Some cells undergoing apoptosis will release cell signals to trigger mitosis which means that some tissue can grow back and remodel.
What genes control the processes that shape organisms?
Protooncogenes - promote mitosis as they code for proteins that promote growth
Tumour suppressor genes - promote apoptosis as they code for proteins that halt cell division
What factors affect the expression of regulatory genes?
Severe psychological stress, pathogens, cell stress, temperature and light intensity
Cyclins and CDKs
Cyclins and cyclin dependent kinases regulate the checkpoints that make sure damaged DNA is removed before mitosis. Cyclins are the regulators and CDKs are catalysts when activated by cyclins, their job is to activate or inactive proteins by phosphorylating them.
