The transcription factors encoded by the pair-rule genes activate the segment polarity genes, whose mRNA and protein products divide the embryo into 14-segment-wide units, establishing the periodicity of the embryo. 

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#Id: 2229

#Unit 11. Evolution and Behavior

The Birth of a Gene - Duplication is the most common way that new genes arise in eukaryotes. 

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#Id: 1076

#Unit 5. Developmental Biology

Many of the genes that determine floral organ identity are MADS box genes, including AG, PI, and AP3 genes of Arabidopsis

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#Id: 8829

#Unit 6. System Physiology – Plant

When PSII receives more light than PSI, plastoquinone becomes predominantly reduced, resulting in activation of the LHCII kinase. The kinase phosphorylates LHCII, resulting in migration of LHCII away from the granal region where it can associate with PSI, thereby adjusting the relative excitation of PSII and PSI.

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#Unit 7. System Physiology – Animal

Norepinephrine produces vasoconstriction via  α1 receptors, but epinephrine dilates the blood vessels in skeletal muscle and liver via β2 receptors

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#Unit 3. Fundamental Processes

DNA methylation and macroH2A contribute to the stable repression of the inactive X chromosome  A. Wutz and J. Gribnau, Curr. Opin. Genet. Dev. 17 (2007): 387–393. inactive specific transcript), which is stably expressed only on the inactive X chromosome.