Term
Explain the link between bicoid and hunchback concentration.
How do we know this? |
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Definition
Bicoid is maternally provided mRNA (there before fertilisation) and hunchback (that is transcribed after fertilization) concentration is dependant upon bicoid concentration.
We can monitor the concentration of hunchback using controlled doses of bicoid. The increase in bicoid is proportional to the increase in hunchback. |
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Term
| Explain how bicoid causes the other genes to cross-regulate eachother. |
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Definition
Bicoid activates hunchback, bicoid and hunchback activate the even-striped (2nd eve stripe). These are in a broad range and so even-striped would have a broad stripe.
However, even-striped is deactivated by giant and kruppel, which form the sharp borders of the 2nd eve stripe. |
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Term
| How are the repeating expression patterns of pair-rule genes used to produce morphological repeating units? |
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Definition
| This occurs when the blastomere has become cellularised. Engrailed acts on the posterior eng of each segment- it is a selector gene (confers the identity of a region for an extended period of time). It first is seen in non-defined stripes and then they become clearer. This is because they are auto-regulatory (stimulate their own expression) and they can down-regulate one another. The other genes are fushi tarazu and even-skipped. |
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Term
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Definition
| Primary boundary in the embryo; cells will not cross it through development. |
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Term
| What positive feedback loop helps define the parasegment boundaries? |
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Definition
| Engrailed is on the anterior side of the parasegment and wingless is on the posterior side. Engrailed stimulates the transcription of sonic hedgehog gene and this stimulates the production of wingless over the parasegment boundary. Wingless also stimulates the transcription of engrailed. |
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