Body plans & Homeobox genes
- Created by: katelingoody
- Created on: 30-10-17 11:29
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- Body plans & Homeobox genes
- Homeobox genes are responsible for determining the body pattern of an organism
- Tend to come in groups called HOX CLUSTERS
- They are regulatory genes
- A homeobox is a section of DNA which can turn other genes on/off by binding to DNA.
- 60 amino acids long
- Necessary to turn homeobox genes on/off.
- Well conserved across plants, animals and fungi.
- HOX genes only present in animals
- Control positioning of body parts
- Mammals have 4 Hox clusters on different chromosomes
- The order that they appear in along a chromosome is the order in which their effects are expressed
- Body plans usually shown as cross sections through an organism.
- Shows fundamental arrangement of tissue layers
- Diploblastic animals- 2 primary tissue layers
- Tripoblastic animals- 3 primary tissue layers
- Animals are segmented- these segments have multiplied over time and are specialised for various functions.
- Shows fundamental arrangement of tissue layers
- Most animal body shapes have symmetry
- Bilateral symmetry is seen in most animals. They have both left/right sides, as well as a head and tail.
- Radical symmetry is seen in diploblastic animals such as jellyfish. They have no left/right sides, only a top and bottom.
- Assymetry is seen in sponges, which have no lines of symmetry.
- Mitosis (cell division) and apoptosis (programmed cell death) are essential for shaping organisms.
- Hox genes regulate mitosis and apotosis.
- In removing unwanted cells by apoptosis, cells cells can also release chemicals which cause mitosis and cell proliferation, thus remodelling tissues.
- Expression of regulatory genes is affected by the environment
- Internal and external influences lead to stress, which can be defined as the condition produced when homeostatic balance within an organism is disturbed
- Internal factors
- Hormonal changes
- Psychological stress
- External factors
- Temperature change
- Change in light intensity
- Internal factors
- Internal and external influences lead to stress, which can be defined as the condition produced when homeostatic balance within an organism is disturbed
- Expression of regulatory genes is affected by drug use.
- Drugs can also affect the activity of regulatory genes
- Thalidomide (morning sickness drug in 1950's) prevents expression of a hox gene, leading to birth of babies with shortened limbs.
- Now used to treat some forms of cancer.
- Homeobox genes are responsible for determining the body pattern of an organism
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